Do-It-Yourself Automotive LPG Conversion
by Tom Jennings Reprinted from: http://wps.com/LPG/LPG-book-final.html#SYSTEM%20DESIGN
World Power Systems, San Francisco CA
Fourth edition, Nov 98. Third edition, Apr 97. Second edition
March 1994. Original printing April 1991. Copyright Tom Jennings
1991, 1994, 1998. All rights reserved.
Table of Contents
 The
vehicle featured in this LPG fuel conversion project -- my 1963
Rambler Classic 550 Station Wagon, with a late-model (well, 1970)
232 ci. 6 cylinder engine. 3,150 lbs. of finely wrought steel.
Substitute your favorite car here.
There already is a practical alternative to gasoline as a motor
vehicle fuel. It's cheap, doesn't require exotic equipment, and is
retro-fittable to many existing vehicles. It's street-legal, even
in California. It produces half the carbon dioxide of gasoline,
vastly reduces other pollutants including dirty motor oil. It's
Liquefied Petroleum Gas, or LPG for short.
This book describes how I built my LPG-powered automobile,
provides some background information, and lists my experiences in
operating an alternative-fuel car day to day for over five years.
My goal is to outline the process I went through, provide the basic
technical information to build your own LPG-powered vehicle, and
give you an idea of what it's like to use it in real-life
terms.
Liquefied Petroleum Gas, or LPG, is the correct name for what's
commonly called propane, butane or bottle gas. It's actually a
mixture of propane, butane, ethane, methane, and other gases.
Physically, it's a gas at room temperature, and compresses into a
liquid at reasonable temperatures and pressures, which is why it's
called Liquefied Petroleum Gas. It's odorless, but has an odorizer
added so that you can smell leaks.
It's non-toxic enough to cook with indoors and heat your house;
indoor warehouse forklifts use it without ventilation; Supermarkets
buff their floors with a propane-powered floor buffer. It's also a
claimed environmentally-safe aerosol propellant, quickly replacing
freon in many cases.
There are a number of reasons why I wanted an LPG car: low
tailpipe pollution; extremely long engine life; 250,000 miles is
routine, 400,000 miles rumored; vastly reduced oil consumption, and
waste oil is less toxic than a gasoline-engined car; and it allows
turning larger, simpler, cheaper, less-efficient vehicles into
practical alternative fuel vehicles. It's also technically
interesting, and I simply like traveling unusual paths.
After nearly ten years of driving relying on my LPG car as
primary transportation, I am hard-pressed to find LPG's drawbacks.
Of the limitations of my car compared to an equivalent gasoline
car, all are because mine is homemade.
For a sense of scale, I'll too-briefly compare some well-known
energy sources to a reasonably efficient gasoline automobile. A
1994 Ford Festiva will carry 4 people plus itself (total: 2200 lbs
or so) about 50 miles on one gallon of gasoline under best
conditions. One gallon of gasoline contains about 37 kilowatt/hours
(KWH), so for comparison purposes this is what I'll use.
(A kilowatt is 1,000 watts; expending 1,000 watts (heating
water, running a motor, etc) continuously for one hour is a measure
of work done, and a kilowatt/hour (KWH) is a decent human-scaled
amount of work; one ``horsepower'' is 746 watts.)
ONE PERSON pedaling an efficient bicycle fairly hard can
generate about 100 watts of energy; kept up for an hour is a fair
amount of work, and in techie terms, is called, appropriately
enough, 100 Watt/Hours, or 1/10th of a kilowatt/hour. Do this for
370 hours, and you're there.
ELECTRICITY in San Francisco costs about 12 cents per
kilowatt/hour. (Electrical utility power is highly subsidized;
actual system-wide cost is much more.) That gallon of gas would be
about $4.44.
Storing electricity is difficult and expensive. To store that 37
KWH-worth of energy, you would need about $4800 worth of hi-tech
lead chloride cells, weighing 2400 lbs -- you'd still have to
generate the energy to put in them. Electric Vehicles (Evs) are
great, but someone else's story.
SOLAR POWER form solar panels (PhotoVoltaic, or PV) generate
electricity ``for free'', once you own them. Today's
state-of-the-art PV technology converts about 13% of the sun's
energy striking them to electricity when aimed properly; a
panel capable of generating 37KWH in 8-hours worth of bright
sunlight would cost $33,500 (96 ARCO M-75's, assuming a better
price than the Real Goods 1990
Sourcebook).
 Good-size
solar PV panel, looks like 180 Watts or so. Installed in a
well-designed system in the right part of the world, adequate to
power a very small house. (See Home Power and Real Goods in
SUPPLIERS & SOURCES.)
HYDROGEN sounds like the perfect fuel until you try to make it
or store it. In theory a non-polluting source, in practice it has
to come from somewhere, and guess what -- commercially available
hydrogen is usually made from petroleum-derived methane. In the
laboratory it can be made by breaking water molecules into its
component hydrogen and oxygen, but it that takes huge amounts of
energy, far more than you recover when you burn the oxygen and
hydrogen later for power. Even with a perfect storage medium and
100% efficient fuel cell, you might as well simply store the energy
you'd use for wrestling with hydrogen atoms and use it directly to
do the work you originally intended. One pound of hydrogen contains
36KWH. It's volume depends on the storage medium.
METHANOL (and ETHANOL) is pretty powerful stuff; at 23KWH a
gallon similar enough to gasoline; 16 gallons of methanol has the
same energy as 10 gallons of gasoline. It can also be produced from
fermentation of organic matter, and apparently in Brazil lots of
commercial fuel alcohol is, making it a renewable energy source
there. Here in the U.S. most methanol production is from petroleum
and lumber-industry byproducts. It's attractive as a motor fuel
because it fits in existing fuel-dispensing systems and equipment,
but not a very clean fuel, pollution-wise; see below.
PROPANE -- LPG is yet another ``byproduct'' of the petroleum
distillation process. By a lovely coincidence of physics these
gases liquefy at reasonable temperatures and pressures, so that one
gallon of LPG (liquified; about 270 gallons in gaseous form)
contains 27KWH of energy; 13 gallons of LPG is equivalent to 10
gallons of gasoline, even though to use as a fuel they are handled
very differently.
LPG GASOLINE METHANOL
lbs/gal 4.24 6.4 6.84
BTU/gal 91,500 126,000 79,400
Boils at -44F 85-390F 149
From an ``alternative'' point of view, alcohol (methanol or
ethanol) seems to be the winner at first glance, because it is a
potentially renewable fuel; if made from fermented organics such as
plants, no more carbon dioxide is produced in combustion than is
bound when the plants are grown or replenished.
Unfortunately there are a number of problems with using alcohol
for existing applications. One problem is the simple fact that no
organically-produced methanol is available in the US, and home
production of decent quantities is not a trivial task. Also,
methanol, because it is a liquid, simply does not burn completely
in an internal combustion engine. The theoretical products of
methanol combustion, as for gasoline combustion, are carbon dioxide
and water. In real life there is unburnt fuel, carbon monoxide,
nitrogen compounds, and various hydrocarbon fragments from
incomplete combustion combined with the high pressures and
temperatures of the cylinder combustion process.
Basically the problem is that liquid fuels are liquid -- even
after vaporization in the carburetor, swirling in the cylinder head
etc, fuel droplets remain unburnt, because of the short time given
for each cylinder to fire to operate the engine.
Gaseous fuels simply don't have this problem -- the individual
fuel molecules are by nature separate, and burn very nearly
completely. This is the major reason that LPG is such a good motor
fuel.
Though the sheer volume of gas needed is intimidating,
fermentation methane, dried and compressed into liquid, would be at
once renewable and non-polluting. Most likely you could have the
same vehicle operate on commercial LPG (long trips), or methane
from fermentation.
Also in LPG's favor is that pound for pound, it contains less
carbon than gasoline or methanol (more of it's energy is bound up
in hydrogen atoms than carbon atoms) -- an LPG powered vehicle
produces approximately half the CO (carbon monoxide) and CO2 per
mile, though only slightly less nitrogen compounds (created when
the high volume of atmospheric nitrogen, some 70% of the air, is
subjected to engine cylinder temperatures and pressures).
Having now used both gasoline and LPG, I far prefer handling
LPG. My now-infrequent trips to gas stations (in other peoples'
vehicles) are like visits to toxic waste sites. It's amazing what
we get used to!
A gasoline spill, by accident, or more ordinary dripping hoses
at a gas station, is a toxic nightmare. In addition to being
exceedingly flammable, gasoline runs into streams and soak into the
soil, poisoning everything it touches. Its vapors are explosive.
It's a known carcinogen. Even if the fire hazard is overcome, the
toxicity lingers on.
An LPG spill is just as flammable (or it wouldn't be a useful
fuel!), but instead of poisoning the environment, it boils away as
fast as it can absorb heat. LPG is non-toxic. It's vapors can
collect in low spots, where it is a fire hazard, since it is
heavier than air. Once the gas has dissipated, there is no further
hazard. Spilled liquid, while rare enough in anything but extreme
circumstances, will give you nasty frostbite.
Basically, we're just used to gasoline, most of us growing up
assuming the stuff is everywhere, and we have systems to deal with
it. LPG is ``new'' and somewhat alien, but on the whole no worse,
and once you're used to it, safe and easy to handle.
One way to think about the physical properties of LPG is to
think about how you'd have to handle water and steam if the
temperature around us was 250 degrees (F). If you were to pour
water on the ground at that temperature, it would immediately boil
into vapor and ``disappear'' into the atmosphere. To store it, you
would need to keep it under pressure, in cylinders strong enough to
hold it, plus a safety margin. This is exactly how LPG acts in our
normal range of temperatures. The boiling point of any liquid (the
temperature at which it vaporizes) increases with pressure; to keep
water in it's liquid state at 300 degree F you'd have to keep it in
a container at just over 67 pounds/square inch (PSI); at 350
degrees F, 135 PSI.
LPG acts the same, but at much lower temperatures; at 80 degrees
F it must be kept at 130 PSI to keep it liquid. The fact that LPG
fuel is a gas, and not a liquid, at first seems like a liability,
but is it's strong point, as you'll see later.
I completed the LPG conversion of my car in October, 1990. When
I first wrote this book, in April 1990, I had only limited
experience with the car, which was covered admittedly poorly in the
first edition. Since that time, I've taken a number of long road
trips. In brief: everything went better than expected. The car ran
great at all altitudes (sea level to 9900 feet), in hot (110
degree) and cold (35 degree) weather. Fuel availability was good in
most areas during daylight hours, poor at night, and in a few
places hard to get. At no time did I run out of fuel, though I
admit I worried about it a lot, not always needlessly.
This seems an appropriate place to mention a lot of information
that doesn't fit elsewhere. I'll simply describe my subjective
experiences of driving an LPG car on my various road trips.
The first thing everyone asks (after ``doesn't it blow up?'') is
``where do you buy fuel?''. We're so used to seeing gasoline
stations everywhere, we overlook the shiny white tanks that LPG
generally comes in.
Fueling up with LPG is a completely different experience from
buying gasoline. With gas stations at nearly every Interstate exit
and highway intersection, the thought of having to search for LPG
is daunting. In fact, it's not that bad. LPG is very common in
rural areas; you start noticing the telltale white tanks all over.
Many rural gas stations have smallish LPG tanks off to one
side.
If your driving habits include constantly running on a
near-empty tank, and getting $2 worth of fuel in the middle of the
night at the last possible, digging change out from under the
seats, you'll have to either change your habits or stick to
gasoline.
On the Interstates, LPG stations are found in truck stops, or on
the outskirts of town. Nearly every large town or city has one of
the regional or national distributors, who generally have the
lowest prices.
Finding LPG during daylight hours is easy, early eves not so
easy, late at night difficult in rural areas, since most LPG there
is non-vehicular. However on a recent trip to Denver, I was able to
easily drive all night, fueling up at truck stops and small towns
in Nevada.
LPG is sold by the gallon; prices vary widely. The lowest prices
are at the distributors themselves, and the highest at the local
mom'n'pop store with a 100 gallon tank for the RV'ers. At a time
when gasoline was about $1.15/gallon, LPG at a distributor in New
Mexico was $0.95/gallon, and a mom'n'pop in California
$1.35/gallon. The lowest I've ever paid was $0.59, the highest
$1.50; as you can see, the prices vary widely. During this time, I
was typically paying $1.20--$1.30/gallon at a typical gas station's
LPG service.
Fuel availability seems to have noticably improved since 1990;
maybe I'm just gettingbetter at spotting them out of the corner of
my eye, but it really does appear to be proliferating, and I'm
uncertain why; there's certainly not many more LPG cars out on the
road that I can see.
I've taken a half-dozen or so long (1,000 mile or longer) road
trips since the first edition of this book. In over 14,000 miles of
driving, I had one mechanical failure due to my LPG system. (I'll
not mention the rock that cracked my windshield on an Arizona
highway in February, the headlight switch that dropped dead just as
I pulled onto a Nevada highway at night, or the taillight fuse that
blew in California when my clock decided to fail.)
The failure was actually a problem built-in from the start, that
caused me grief on a number of trips, and incorrectly diagnosed in
the first edition (how embarrassing). See the MY PROBLEMS
section for details; but briefly, I had two check valves in the
fuel-filler system that wanted only one, and they fought each
other. Once I installed the correct part the problem went away
forever. The parts supplier was partly at fault, as I bought the
complete system from them. I had other problems with this supplier
as well.
Running out of fuel on the road would be a major inconvenience,
as even AAA doesn't seem to know anything about LPG motor fuel.
I've worked out a simple, safe and reliable ``gas-can'' system; see
below for details. I've intentionally used it a dozen times (not
once have I ever been forced to go fetch fuel) and it works just
great.
As of January 1990, California LPG vehicles need to be
``smogged''. The car simply has to meet the smog specifications for
that model and year, which is amazingly easy. The testing machine
has a setting for ``propane'' fuel. When the auto center I went to
found out the fuel was LPG, they panicked. It took a call to the
Smog Board arbitrator to get it all straightened out. California is
the most stringent state in the U.S. for smog controls.
Most LPG station attendents I ask say they fill no, or very few,
LPG vehicles, and most of those are pickups; one on Route 5 said
one or two a month.
In California you can also get a sales tax exemption -- a
sticker you apply to your window, that exempts you from paying
sales tax on LPG motor fuel. It costs $36 (Jan 1991), is good for
one calendar year. Call the Franchise Tax Board for details. I had
to explain to them it was for a passenger car; the person on the
phone started rattling off commercial GVW requirements. Presumably
most of their customers are truck fleet owners. I've found that few
LPG dealers even know they're supposed to be charging road tax, so
it's become moot. I never bothered with a tax-exampt sticker.
On the road, I asked a veteran Canadian RV'er with an LPG pickup
(150 gal. tank!), what's the situation on LPG availability around
the U.S. He said California was the worst. (If this is the worst,
things aren't so bad.) I wonder about the dense NorthEast.
A quick scan of the Yellow Pages under ``GAS - PROPANE'' for San
Francisco lists 15 locations.
U-HAUL's national ``RV World'' stores always carry LPG, and some
are open 7 days. Most campsites carry LPG too.
All KOA Kampgrounds have LPG, some 24 hrs/day.
On a trip down the Northern California's Route 101, I found LPG
to be plentiful, though somewhat spotty at night.
Join AAA and request their list of campgrounds for areas you
travel in. The campsite listings list propane services. Bug AAA
about LPG fuel-availability guides, vehicles, service; they need to
be told we're out here.
Other avenues to follow that I haven't yet -- truck stop
franchise chains, oil companies, service companies, all want to
sell you their goods and services. A call or letter asking where to
buy their products should be fruitful.
Engine oil stays yellow and odor free 10,000 miles after an oil
change. It never gets as dark and smelly as it did on gasoline.
Many LPG dealers say that 16,000 miles is the recommended oil
change interval; I just can't bring myself to go that far, and oil
is cheaper than engines, I generally change mine at 10,000 miles or
six months. There are LPG-specific motor oils, and the back of the
can propaganda talks about reduced acids from longer oil change
intervals, and reduced shear damage; while this hardly constitutes
oil chemistry research I'll take the hint and stick to 10,000 miles
per oil change!
 A typical
LPG fuel filler with the locking door open. The round Acme fuel
connector is in the center, and the gas vent in the lower left
corner.
This construction book is only the first phase of my project,
and unfortunately not the interesting part, regarding truly
alternative fuels. I don't have bags of money, and I have to
arrange things in a manner I can actually get them done, and still
accomplish my long-term goals.
Access to decent test equipment is the obstacle to getting real
numbers on emissions. Commercial smog stations have $30,000+
invested in their machine, and will charge you big bucks ($45 per
test) in order to recoup the expense. Home type equipment I don't
have, and haven't yet investigated, as to accuracy and sensitivity
-- it must be able to measure extremely low levels of hydrocarbons
(HCs) and carbon monoxide (CO).
From a non-global-system perspective, LPG is a winner. Your
vehicle will last far, far longer, maintenance is simpler and less
frequent, so you can at least slow down your part of the
consume/discard cycle. And you can do it today.
From a global-system point of view it's definitely a short-term
gain, as you immediately eliminate the toxic parts of vehicle
emissions. At the moment it is not a major motor fuel, and you get
to work in the margins of the petroleum industry, and if you can
produce your own fuel gases, get out of the loop entirely.
The ``typical'' older American car or light truck is a perfect
candidate for LPG, as they tend to have large displacement,
carbureted, water-cooled engines. Four, six, eight cylinder doesn't
matter.
Air-cooled engines would require a different converter/regulator
design. I don't know what an LPG carburetion system for a
fuel-injected engine would look like. Better ask an LPG service
center.
I'll assume that you more or less understand the major systems
in an ordinary automobile -- an internal combustion engine that
converts stored chemical energy (fuel) into motion by burning it, a
transmission and such to move the wheels, suspension, brakes, and
all that to make it practical. The only thing different in an LPG
vehicle is the fuel system.
A basic LPG fuel system isn't really much different than a
gasoline system. There's a fuel tank, some hoses, a fuel filter,
and a carburetor. The biggest difference is that LPG is under
pressure, so the tank is heavy gauge steel with various safety
features, the filter doubles as a fuel shutoff, and there's a
regulator/converter that turns the liquid LPG to a gas explicitly
before entering the carburetor.
The hose used to carry LPG to the engine compartment is heavy
neoprene covered with a stainless steel mesh, with a fabric
covering. It's rather bulky (about 3/4 inch), but rugged and
designed for 1750 pounds per square inch (PSI). An LPG tank left in
the sun will generate a few hundred PSI, so there's more than
enough safety margin there.
You have the choice of installing an LPG only or dual
LPG/gasoline system. As you might guess, the dual-fuel setup is a
compromise; you'll get maximum performance, simplicity and economy
with the single fuel setup. That is what I chose. I talked to the
owner of a 1970 GMC pickup who converted to dual fuel when the
truck was new (181,000 miles, no motor overhaul yet) and says he
runs mainly LPG, and gasoline when LPG isn't convenient. You may
have trouble with the carburetor gaskets drying out and such; talk
to the LPG equipment dealer for details. The GMC owner had no
complaints, so maybe all that's overrated.
LPG experts will tell you two things you will need to make it
all work -- a good ignition system and a good cooling system. And
they're absolutely right. LPG requires a good hot spark, and an
ignition marginally OK for gasoline will run terribly on LPG. I had
a classic textbook example of this happen to me; read about it in
the PROBLEMS section.
An electronic ignition is probably a must. My car had
old-fashioned points and spark coil, to which I added an
Autotronics Multiple Spark Discharge ignition, which cost me $89 in
1986. It works flawlessly, simple to install, and a set of points
now lasts 50,000 miles.
You need a good cooling system, not because the engine runs any
hotter, but because the LPG regulator/converter uses engine coolant
to provide the heat to convert the liquid LPG to a gas. (Even
``cold'' water works -- it just has to keep it above freezing.)
An LPG conversion does not require any special modifications to
the engine. Since LPG has fewer BTU's per pound than gasoline, and
the engine is designed to take in a fixed volume of fuel/air
mixture, you'll get about 10% less horsepower for a given engine,
at full-throttle. To help compensate, LPG has an octane equivalent
of about 110 -- meaning you can advance the ignition timing a lot.
The actual loss depends on the specific engine, but it will
probably not be noticeable.
p>
I built my engine specifically to run LPG, back in 1988. Since I
knew it would be a while before I could afford all the LPG
equipment and get around to installing it, the motor had to run on
gasoline also. The compromise was easy, and not much of a
compromise.
There are three areas affected by fuel choice -- compression
ratio, cam timing, and exhaust valves and seats. The biggest
compromise was compression. 12 to 1 isn't too high for propane, but
is too high for gasoline. My engine was about 8 to 1 stock. The
machinist (Mike at Folsom Auto Supply) found a stock piston from
another engine that raised compression to about 10 to 1, a decent
compromise for no additional cost; since I was boring the cylinders
.030" oversize I had to buy new pistons anyways.
I had a camshaft custom made by Crower Cams, though any good cam
grinder should be able to do it. I told them over the phone my
application (to their credit they didn't laugh) and told 'em dead
stock except for the compression ratio, and, importantly, to move
the torque peak much lower (I never rev the engine beyond 3500
RPM.) They came up with the following: 240 degree duration intake
and exhaust, .390" valve lift, with intake valves open at -13 ATDC,
close 15 ABDC, exhaust valves open at 23 BBDC, close at -21
BTDC.
[1994 note: This particular camshaft was a terrible choice; the
cam grinder designed a low-vacuum camshaft that's proven disastrous
with LPG carburetors, which use engine vacuum at low speeds to
determine fuel/air ratios, and the car runs constantly rich with
poor mileage. The camshaft was replaced with factory-stock in late
94. The rest of the original camshaft discussion has been
deleted.]
The last item to improve is to use hard exhaust valves and valve
seats, such as Stellite. Hard valves were not available for my
engine, alas, though I was able to get hard valve seats. The
ignition temperature of LPG is somewhat higher, though not enough
to worry about if you can't get them; I doubt it will make even a
5% difference in valve life.
[1998 note: the engine now needs it's valves rebuilt or
replaced, with about 90,000 miles on them. It runs fine, but
mileage is dropping. I have annual cylinder compression data
starting 1991, when it was 140-145 lbs/sqin; it's now dropped to
115-125 lbs/sqin, which increased slightly with a squirt of oil. I
may renew my search for hard valves for this engine.]
There seems to be two major manufacturers of LPG systems, Impco
and Century. Impco seems to be the simplest and easiest to install,
and is what I used.
An LPG system consists of a filter/shutoff, converter/regulator,
and carburetor chosen to fit engine size, and hoses, connectors and
other more common components. Component costs don't vary much with
size; if I remember correctly the next-size-up regulator/converter
was $10 more.
 LPG fuel
tank as installed in my Rambler. This tank was meant for a large
van, and is rated at 20 gallon capacity; in fact, it only holds 18
gallons of fuel. (The photo greatly exaggerates how much the tank
actually hangs down.)
The fuel tank is the single most expensive component, and the
hardest to fit. Since my car is LPG-only, I removed the gasoline
tank and put the LPG tank there. If you are doing the installation
yourself, you'll have to carefully choose a location. Most
passenger car and van installations will use ``siamese tanks''; two
smaller tanks welded side by side to make a larger, more compact
tank. Alas, they are also more expensive. I was able to get one for
cheap because the dealer had a stack of them from a contract that
fell through. Each installation will be different. Visit the dealer
with tape measure in hand.
[1994 note: I've noticed that wrecking yards devoted to trucks
and commercial vehicles generally have lots of used LPG tanks.
Since there's very little market for them you can get 'em dirt
cheap. A tank nearly identical to my new $400 tank was available
for $50 used. Live and learn. Make sure it's not rusted!]
[1998 note: Earlier this year I replaced the 18 gallon tank with
a brand new 35 gallon tank (28 gallon fuel capacity). What a
refreshing change! At about 14 MPG propane average-worst-case
mileage, it gives me a 400 mile range full-to-empty. To do this I
had to sacrifice my spare tire compartment, and will locate a
"continental kit" type bracket to mount it externally. Since this
car is mainly for road trips it's not a problem for me. My next
conversion will be to my "new" 1975 Gremlin X V8, where I should be
able to fit the same 35-gallon tank and keep the spare inside,
too.]
With one exception, the LPG fuel tank must be installed
outside or under the vehicle, and all hoses outside the passenger
compartment. Safety is the issue, and no different than a
gasoline-powered vehicle. The one exception is trunk mounting of
the LPG fuel tank, especially in sedan-type automobiles with the
gasoline tank still in place. In this case, the trunk area {\it
must} be sealed off from the passenger compartment with foam, and
vents to the outside cut in the body at the lowest point, to allow
potential LPG vapors to escape. (There are also tanks and add-on
devices to completely enclose the hoses and fittings in a ventable
flexible container, such that the tank could be in the trunk
safely.)
A good start for a new tank is the Manchester Tank Co. in
Lynwood, CA. They publish a catalog of their tanks. My new 35
gallon tank cost $595.00 (June 98).
The filter/shutoff does what it's name implies. The filter
element lasts 100,000 miles, and mainly keeps out junk that may
have been in the tank when it was made; the fuel itself is quite
clean. Since the fuel is under pressure, the shutoff turns off the
fuel when the engine is not operating. The Impco system uses engine
vacuum to do this; some models, and the Century brand, use a more
complex electrical system.
The fuel hose is high-pressure stainless-steel-mesh reinforced
neoprene, and the dealer should stock just about any size required.
It's fairly expensive, but make sure you get enough -- the only
thing worse than too long is too short! Under no circumstances
should you run fuel lines -- LPG or gasoline -- through the
passenger compartment.
You will also need a handful of connectors for the hose. They
are easy to install -- after cutting the hose-end nice and square
and clean, you screw on the outer part counter clockwise
first, then screw the inner part into that, tighten snugly (
Before and after photo here (9K).).
The carburetor is fairly easy to install. You'll get an adapter
to fit the intake manifold and the throttle lever is made to
accommodate a custom fit. It took me a few hours to lay it all out,
and make a throttle linkage with hand tools.
Last but not least -- the fuel gauge. You can use your existing
in-dash fuel gauge. There is a wide range of tank sender units to
fit most cars, that connect to the original wiring and work in the
usual manner. A 90-Ohm unit fits most cars. You'll also need a
fistful of sheet metal screws and plumbers tape, for mounting the
fuel hose to the car. A decently stocked ``junkbox'' helps, though
most everything else you'll need will come with the components you
buy.
Overall view of the engine
compartment (38K). The convertor/regulator (a) and
filter/shutoff (b) are visible on the right inner fender, and the
carburetor (c), in the foreground, has it's air filter in
place.
Figure out where the LPG components will go. Placement isn't
critical, but you will want to keep these things in mind.
 Closeup
of my LPG fuel tank installation. A very tight fit.
1. Mounting the tank will be the hardest part; gasoline tanks
are made-to-fit the car, and LP tanks don't come in such convenient
shapes. Mine fit fairly well, but hang down a bit).
2. Running the LPG hose requires a bit of care. You don't want
it exposed where running over a rock or curb could crush it, and
you should attach it to the underside of the car every foot or so,
as any flexing will eventually wear through the protective
covering. After a week of operation, I found mine had been chafing
at a few places. Attaching it every 12 inches with plumbers tape
solved that.
3. Mount the regulator as low as possible, (less sensitive to
coolant level) and close to the carburetor. My installation came
out pretty neatly, with a one foot section of hose between the
filter and regulator, and an 18 inch piece of vapor hose to the
carburetor. (For most installations you can simply connect the
filter/shutoff and regulator/converter together as a unit with a
short pipe nipple instead of hose.)
Close up photo (31K) of the major
components. Regulator/converter (a) and filter/shutoff (b) mounted
on the inner fender. Note the water connections coming from front
of the engine (left) and heading up to the heater on the firewall.
The LPG hose is at (c) and the vapor hose to the carburetor is
(d).
4. The water connections aren't fussy; as long as you get decent
water flow, and keep the radiator full, you're all set. (I plumbed
min in parallel with my heater, and installed a water valve to
restrict the hot water through the regulator/converter to a
trickle; this leaves plenty of hot water for the heater.)
[1998 note: my original water system was stupid. It's simply
better to by the "H" fitting, basically two parallel pipes with a
small cross pipe; you put the two larger legs in series with the
hot water to the heater; the small bypass assures that a small
amount of hot water flows even when the heater is off. The
converter is simply connected in series with the heater.
5. Carburetor installation is simple. You may have to fabricate
a throttle linkage, but it's designed to be easy, and you can get
adapters for nearly anything. The Impco carburetor has a throttle
lever that fits on either side of the throttle shaft, and there are
many adapters available that rotate the carburetor 90 degrees. It's
also far shorter and more compact than a gasoline carburetor, so
there will probably be no interference with other components.
 Carburetor, minus air filter, with the vapor
hose coming over the top of the engine. Note the
regulator/converter and filter/shutoff barely visible in the
background.
6. The fuel filler system is more complex than for gasoline, but
still simple. It consists of a brass threaded ``Acme'' adapter, and
a small gas vent valve. Get the more expensive model with a locking
cover; the other style available is for fork trucks and such, and
any idiot wandering by can let all your fuel out by opening the gas
vent valve! The cover type also looks much better.
Fuel-filler system with the locked door
open. The Acme filler connector is in the center; the vent valve is
in the lower left corner.
When you first install the system, it will be empty of fuel. I
used my ``gas-can'' (see below) to purge the tank and put a gallon
or two of fuel in the system and check for leaks.
First, use plumbers' bubble-leak detector or soap solution to
check for leaks. I used a pump sprayer with Dr. Bronners liquid
soap and water.
1. Open the LPG liquid valve, and look, listen and smell for
leaks. A squirt of soap at all connectors helps. If you find a
leak, try tightening a bit; if a little is good a lot is not
better; you'll just wreck things. Check for leaks up to the
filter/shutoff.
2. Start the car -- no fancy preliminaries. The
regulator/converter will purge itself of air, and it should start
within 5 - 10 seconds. The throttle must be opened a small
amount.
You will have to tweak the idle speed and mixture. I set the
idle too high at first, and adjusted it after it was running.
3. At this point, check for leaks after the filter/shutoff.
4. Tune up the car normally. No special settings are required,
and for emissions/legal purposes, none desired. Set the ignition
timing dead stock. If the car was previously in tune, all you
should need to do is set the idle mixture and speed on the new
carburetor.
5. After a thousand miles or so, check the spark plugs. Spark
plugs will last considerably longer, as there are no fuel additives
to build up on the insulator during combustion. Check for the right
heat-range plug -- if the insulator color is too white, or if it
looks burnt, get plugs one range colder.
There are some problems unique to LPG fuel systems, and because
the components are mechanical devices, they can fail. Here's some
tips on troubleshooting and repair.
In general, if you find frost on LPG components (liquid service
valve, filter/shutoff, regulator/converter) you have a problem. If
it happens to the liquid service valve, it may be that the internal
excess-flow safety valve snapped. Close the valve, wait a few
minutes for the frost to dissipate, and reopen the valve.
If the converter/regulator is frosted, you have an
engine-coolant flow problem. Assuming it's installed properly, it
probably means low coolant level, a loose waterpump fanbelt, bad
water pump, or other mechanical failure. Normally, the
converter/regulator runs about as hot as the radiator.
If your engine ``runs out of fuel'', and you've checked the
obvious (tank empty?) you can check for proper fuel flow right up
to the carburetor, component by component. The following applies to
Impco systems, but the same approach works for all
manufacturers.
1. Disconnect the vacuum hose that goes to the filter/shutoff,
at the manifold end.
2. Disconnect the vapor hose from the carburetor.
3. Suck on the vacuum hose. (This operates the shutoff, allowing
LPG to enter the regulator/converter; you'll need to supply a
constant source of vacuum to the filter/shutoff to keep it open for
testing the fuel supply.) You should hear LPG vapor escaping the
vapor hose. If vapor is available, the problem is in the carburetor
or elsewhere in the engine.
4. If there is no vapor after step 3, and the filter/shutoff is
connected to the regulator/converter with a hose (as opposed to a
short pipe nipple), loosen the connector between the two as you
suck on the vacuum hose. Liquid LPG should escape (keep your body
out of the way). If it does, the regulator/converter is faulty. You
can disassemble the regulator/converter and clean it; it contains
only rubber diaphragms and a few springs.
5. If no liquid LPG is available, either the filter/shutoff is
dead or the LPG hose from the tank is crushed or plugged. Turn off
the liquid service valve on the tank, and disconnect the main
supply hose at the filter/shutoff. Then momentarily open the liquid
service valve; LPG should rush out of the hose into the atmosphere,
quite noisily. If not, the hose is plugged. If it does, the
filter/cutoff is suspect.
Only on long trips, when filling up, the fuel would enter the
tank extremely slowly, less than a gallon a minute. At times, at
high temperature especially, the problem became severe. I even took
it to the LPG dealer I bought the parts from, and they were stumped
as well.
Finally it failed, and hard. I had just driven 280 miles, about
my range limit, to Farmington New Mexico. I went to fill up at a
KOA Kampground, and the definitely empty tank would not take a
single gallon of fuel! Long story short -- I managed to get to an
actual LPG vehicle service station (Randall's Repair, see
SUPPLIERS AND RESOURCES, and determined that the check valve
on the fuel-filler was sticking. However the problem persisted
after replacement. Randall then noticed that I had two check
valves; one built into the tank (required) and one at the
fuel-filler, where the hose is connected. There can be only one
check valve -- when there's two, they fight each other under
pressure and essentially don't open more than a crack. I replaced
the filler-neck check valve with a straight-through filler --
problem disappeared.
I had to remove and replace one connector, where the hose from
the tank fitted to the filter/shutoff. The brass fittings
connecting the filter/shutoff to the regulator/converter leaked; I
had to remove them and assemble with teflon pipe dope (which I
should have used when I first assembled it).
I also had a textbook case of ignition troubles. On my first
highway run, the engine started ``cutting out'' at high speeds, and
when I slowed down to about 50, it smoothed out. Since the only new
thing on the engine was the LPG system, I theorized various
complicated fuel problems. When stumped, I called the dealer, who
asked ``does it backfire through the carburetor?'' to which the
answer was ``yes'', which always means -- ignition problem! But
it's the same ignition I've had for years! No kidding -- and by
wiggling and tugging ignition wires, I found the wire from the
distributor to the electronic ignition was oily and poorly
crimped!
I crimped on all new ring terminals, and soldered them all for
good measure. I also found a crack on the ancient (ca. 1970) spark
coil, and replaced it for good measure. No more problems! The moral
is that LPG makes higher demands on the ignition than gasoline, but
nothing that a decent system can't handle.
No one I talked to had ever heard of a ``gas can'' for LPG,
something I thought was mandatory for a practical vehicle. Standard
practice is apparently to tow an out-of-fuel vehicle to a filling
station! I also wanted to be able to carry extra fuel for when I
couldn't find a filling station on long trips (which has turned out
to not be a problem).
The solution turned out to be easy. I bought a standard LPG
container, and made up a special hose and adapter to fit it. One
end is a standard POL tank connector, and the other is the special
fuel filler connector, with about three feet of size #6 hose.
 The gas
can components; the 5-gallon tank on the right and the made-up hose
(POL one end, Acme the other) on the left. In the foreground are
two nice accessories; an adjustable wrench for the POL connector
and some spare O-rings for the Acme connector.
Portable LPG containers are meant for dispensing vapor for camp
stoves and the like; all instructions say to operate them in an
upright position. This is because the vapor boils off the top of
the liquid in the container, like a tea kettle, and tipping would
cause liquid to flow out -- which is exactly what we want. Here's
how to fill your car from your gas can:
 Donna
giving the ol' Rambler a fill up. Notice that the gas-can is held
upside down.
1. Fill the portable LPG container normally.
2. Connect the hose to the portable LPG container.
3. Connect the fuel filler to the car.
4. Turn the portable container upside down.
5. Open the LPG container valve while holding the tank upside
down. Close the valve when you've dispensed enough fuel, or the
hissing (indicating fuel flowing from the can to your car)
stops.
(When dumping gasoline into a car tank, gravity moves the fuel,
and the air displaced by the liquid gasoline simply flows out the
filler neck. Not so with LPG -- at a filling station, LPG is forced
into the tank with a pump, with the vent open to detect a full
tank.)
When you open the valve at step 5 above, the pressure in the
gas-can will force LPG into the car's tank, until the pressure is
the same in both tanks. Luckily -- the car tank is so much larger
than the gas-can that nearly all the LPG will enter the car tank.
With my 20 gallon car tank empty, and a 5 gallon gas-can containing
4.5 gallons (its maximum capacity), about 4 gallons of fuel are
delivered into the car's tank.
For added safety and to prevent loss by leakage or the valve
opening, I disconnect the adapter hose from the tank, storing it in
a plastic bag to keep it clean, and install a brass plug in the
tank, and tighten it. Even if the valve is opened, LPG will not
escape. I keep a 5 gallon tank bungie-corded in the back of the
car, with room for a second on long trips. I also use the same can
for campsite-cooking!
Here's some things you might want to keep in the car:
A 10 inch adjustable or 7/8 inch open-end wrench, for the
gas-can hose fitting. At the least, you'll need one to remove the
gas-can hose when you fill the can.
Get a bunch of spare O-rings for the filler neck. They are cheap
to replace, and will eventually wear out, and I had mine fall out
once after a fill up. Without one, you won't be able to fill the
tank!
Store the gas-can hose in a plastic bag to keep it clean.
Here's a breakdown of costs from my receipts for this project.
I've arranged the tables with the major, not-optional items at the
top. If you can scrounge hose and connectors and other useful
doodads obviously you could save a lot of money.
The following items are essential, but probably scroungeable to
some degree. You might also check truck junkyards, as many
commercial and fleet vehicles use LPG. Used equipment is fine, as
long as it is undamaged.
(Prices are from 1990)
Major Components
Cost
Filler Valve Assembly 45.00
filter/Shutoff, Impco VFF30 56.50
Converter/Reg., Impco Model L 110.00
Carburetor, Impco CA125 67.00
CI-28 Air Filter Cover 9.44
K&N Air Filter 13.00
Fuel tank, new (varies) 400.00 estimateThe LPG fuel tank is obviously a non-optional item. It is the
single most expensive component, and the hardest to fit. The price of
the LPG fuel tank will vary widely, depending on your application.
Used tanks are a definite possibility.
These are definitely candidates for ``junk box'' items. The
exact quantities will depend on your installation; for example, you
could eliminate a foot or so of hose and the connectors and pipe
fittings between the filter/shutoff and regulator\slash converter
if you had the room to connect the two with a short pipe
nipple.
Major Components
Quan Cost
LPG fuel line, #6 14 ft $2.54/ft (tank to convertor)
LPG fuel line, #8 4 ft 3.32/ft (tank to filler)
LPG fuel line, #4 4 ft 2.64/ft (vapor bleed)
1" Vapor Hose 2 ft 3.68/ft (convertor to carb)
Vacuum Hose 3 ft 1.00/ft
90 degree Elbow, #6 4 6.50 ea
45 degree Elbow, #6 1 1.28 ea
Straight Connector, #8 1 3.28 ea
Straight Connector, #4 2 1.84 ea
Vapor Hose Elbow 2 1.44 ea
Home Power Magazine, Box 130, Hornbrook CA 96044-0130
(916)-475-3179 Aptly subtitled ``The Hands-On Journal of
Homemade Power''. Subscriptions available.
Real Goods Trading Co, 966 Mazoni St, Ukiah CA 95482
(800)-762-7325 (in CA (707)-468-9214) Their Alternative Energy
Sourcebook really is ``A Comprehensive Catalog of the Finest
Low-Voltage Technologies'', each section containing background
technical information on batteries, power sources, lighting
systems, etc.
Suburban Propane LPG components, systems and fuel. Check
the Yellow Pages for one near you.
Solar Mind Magazine, 759 South State \#81, Ukiah CA
95482 (707)-468-0878 Issue #3 was on hydrogen vehicles and
solar/hydrogen sources. Subscriptions available.
The Propane Directory, compiled by Liquefied Gas
Directory of America, Inc., 2888 Highland Drive, Salt Lake City UT
84106 I have no further information at this time, even whether
or not they still exist.
Folsom Auto Supply, 1048 Folsom St, San Francisco CA
94103 (415)-861-0800 Auto parts supply and machine shop
service. They use water/alkali solvents in their hot-tanks instead
of petro-based solvents.
Handbook of Chemistry and Physics, Chemical Rubber
Company, 41st edition.
Pocket Ref, by Thomas J. Glover, Builders Booksource,
1817 4th St, Berkeley CA 94710 (415)-845-6874 An indispensible
pocket version of the CRC book (sort of almost, but better) for
modern times.
Addendum to WPS LPG automotive fuel conversion
This is the
addendum to the original How-To...LPG booklet, written in 1990. A
lot has happened since then, though amazingly what's in the booklet
is still correct. This addendum covers some of the hard parts that
followed, such as fuel efficiency.
This addendum contains followup technical, operational, and
subjective data that I simply didn't have when I wrote the booklet
-- obviously missing was fuel mileage data, long-term operational
and tune up issues, reliability, etc. While these are not really
adequately dealt with here, it's probably all I'll ever do on
it.
The real problem with this whole project, from a documentability
point of view, is that it wasn't simply a science project -- it was
also my daily transportation, a fun toy, an art project (I'll cover
that part of this car in a separate, much more-fun document, in the
next few months XXX years). When I started this in 1987--1989, I
was quite poor, using scrounged and occasionally inadequate parts
for the rest of the car, necessitating doing some things twice.
Everything done on this project during that period happened in
extreme slow-motion, if at all.
The fundamental drive behind this project remains: if gaseous
fuels are so good for internal combustion engines (mainly in terms
of overall fuel efficiency and vastly reduced emissions) why isn't
it common? In essence, is there a catch? The answer remains no --
there is no catch. It's industrial laziness, and lack of vision on
a national level. And yes, this is not a final solution to any
transportation problem, only one component in the existing
system.
-- Tom Jennings, January, 2003
FUEL MILEAGEFuel mileage on
LPG for my car is, considered as a system, fairly good. A
factory-stock 1963 Rambler Classic Wagon, outfitted with manual
overdrive transmission and 196 ci. (3.2 liter) engine, got 19MPG
best case on the highway, which works out to 6630 BTUs of energy
per mile. Mine has a much-newer 232 ci. (3.8 liter) engine, a
non-overdrive automatic transmission; total 1996 average fuel
mileage was 14.22 miles per gallon LPG, about 6444 BTUs per mile,
equivelant to 19.55 MPG gasoline. Considering my larger
engine/less-efficient transmission, I'm netting a decent
improvement over the best this car ever could do on gasoline.
(I started recording fuel consumption/mileage data in 1994; with
a few gaps due to screwups on my part, I have a record of every LPG
purchase, odometer reading, date and usually location since.)
(September 2002 -- a recent trip from Los Angeles to Santa Fe
and back, with a lot of meandering, some 3000 miles, the mileage
remains over 14 mpg LPG, with a peak (300+ miles) at 15.6 mpg LPG,
approximately 21 mpg gasoline equiv.)
These improvements are due to not to a magical fuel, but to a
vastly but simply improved fuel and ignition system. Hand in hand
with improved mileage goes exhaust emissions; while I don't have
complete data on before/after emissions, the emissions improvement
is mostly due to LPG fuel:
SMOG RESULTS HERE
Relative fuel usage, compared in BTU per mile. Assumes 60 mph, as mileage
is measured at more or less that speed on long trips; presumably BTU/mile
is lower at lower speeds due to wind resistance and internal friction.
BTU::fuel data from http://usapc.army.mil/alt_fuels/documents/Energy%20Equivalents%20of%20Various%20Fuels.pdf
LPG Gal/ BTU/ equiv gasoline
MPG Mile /mile MPG
11 0.091 7664 14.88
11.1 0.090 7595 15.01
11.2 0.089 7527 15.15
11.3 0.088 7460 15.28
11.4 0.088 7395 15.42
11.5 0.087 7330 15.55
11.6 0.086 7267 15.69
11.7 0.085 7205 15.82
11.8 0.085 7144 15.96
11.9 0.084 7084 16.09
12 0.083 7025 16.23
12.1 0.083 6967 16.36
12.2 0.082 6910 16.50
12.3 0.081 6854 16.63
12.4 0.081 6798 16.77
12.5 0.080 6744 16.90
12.6 0.079 6690 17.04
12.7 0.079 6638 17.17
12.8 0.078 6586 17.31
12.9 0.078 6535 17.44
13 0.077 6485 17.58
13.1 0.076 6435 17.72
13.2 0.076 6386 17.85
13.3 0.075 6338 17.99
13.4 0.075 6291 18.12
13.5 0.074 6244 18.26
13.6 0.074 6199 18.39
13.7 0.073 6153 18.53
13.8 0.072 6109 18.66
13.9 0.072 6065 18.80
14 0.071 6021 18.93
14.1 0.071 5979 19.07
14.2 0.070 5937 19.20
14.3 0.070 5895 19.34
14.4 0.069 5854 19.47
14.5 0.069 5814 19.61
14.6 0.068 5774 19.74
14.7 0.068 5735 19.88
14.8 0.068 5696 20.01
14.9 0.067 5658 20.15
15 0.067 5620 20.28
15.1 0.066 5583 20.42
15.2 0.066 5546 20.56
15.3 0.065 5510 20.69
15.4 0.065 5474 20.83
15.5 0.065 5439 20.96
15.6 0.064 5404 21.10
15.7 0.064 5369 21.23
15.8 0.063 5335 21.37
Until recently, the biggest annoyance of using this
car as a daily-driver was due to the combined factors of fuel
availability, vehicle range, and tank-filling ambiguity. The
problem wasn't miles per gallon, per se, but the real-life vagaries
of availability.
To illustrate: in a gasoline car, in general around-town
driving, you might drive until you know you have only a few gallons
left, then fill up at your leisure at one of the plentiful 24-hour
filling stations. You might put off filling up until the next day
if you're in a hurry.
For example, you have a 14 gallon fuel tank, and get 20 MPG, and
stop at a filling station when you have two gallons remaining; when
you add fuel to the tank, you easily get within 1 gallon of full.
These factors combine to give you an average-worst-case practical
range of (11 gal*20mpg=) 220 miles between fillups.
I originally built this car with an 18 gallon LPG tank (at 80%),
and get 14 MPG, with decent efficiency, as noted above. Now most of
my filling-stations are closed after 5pm and on Sundays; in general
I don't like being under 1/4th full, which is about 4 gallons
(though I'll certainly run to the grocery store without worry).
When I add fuel, or more accurately, when the poorly trained,
slightly fearful low-level employee at the LPG filling station
pumps fuel, I frequently do not get a truly full tank; I can't
count on having more than 16 gallons in my 18 gallon tank. These
factors combine to give me an average-worst-case practical range of
(12 gal*14mpg=) 168 miles between fillups. If I don't fill up
Saturday, I can't do much driving on Sunday without a search for
fuel.
(The above applies mostly to local driving; on long road trips,
the distances covered generally means you find LPG pretty much
anywhere, though lessened on Sundays.)
The solution to this is obvious -- since I can't change
availability, increase tank size! In February 1997, I installed a
35 gallon/28 gallon liquid capacity tank that increases my
effective range to 300-350 miles, which utterly transformed the car
-- I buy fuel every few weeks, and on long road trips, buy fuel
once per day. For local driving, I sometimes drive to a dealer in
Gardena (from Hollywood) and fill up -- it's worth it when you're
buying 20 gallons at $0.81 per gallon. If I'm lazy I pay $1.40 per
gallon at a tool rental place three blocks away.
I can't emphasize how much this has improved the car. The
downside was, I had to gut the trunk space under the rear of the
station wagon to mount the tank; until I find or make a
"continental kit" for the spare tire it sits on the roof (ugly). As
mentioned in the LPG Book, commercial LPG tanks come in
standardized sizes and shapes, and are therefore not contoured to
the chassis like OEM gas tanks.
Take this as a BIG HINT -- you want absolute maximum fuel
capacity for a daily driving LPG car, I would suggest my rule of
thumb, a real 300 mile range that leaves you with a few gallons for
peace of mind. And you must do this safely -- no tanks or lines in
the passenger compartments, etc -- with off-the-shelf parts.
I've gone
through too many iterations of LPG hardware to get where I am. A
lot of it is certainly my own inexperience, but a too-large portion
of it is incredibly poor advice from so-called experts and a
complete lack of interest and documentation from equipment
manufacturers.
I'll skip all the excruciating detail. Suffice to say I have a
nice normal inline-six of 232 cubic inch capacity (about 3.8
liters) that produces only about 90 horsepower but tons of nice
twisty torque. The engine is now dead-stock except as follows:
Impco model CA125 LPG carburetor
Impco model 'L' LPG convertor
Autotronics MSD-5 electronic ignition
Autotronics 4046 Close-Loop Oxygen Controller
1979 AMC distributor/electronic ignition
Two-wire oxygen sensor in tailpipe
This stuff is not expensive. The CA125 carburetor is probably
the most common LPG carburetor, has two moving parts, and
requires a $50 tuneup every 50,000 to 100,000 miles. Mine was
new in 1989 and has been tuned up (replace diaphragm) once,
in Jan 1996. (Impco's patents ran out on the CA125, and it is
now cloned; in fall of 2001 I bought a brand new Nolff CA125
mixer for $59.00, less then the cost of the Imco brand rebuild
kit!) Before I installed the 4046 Oxygen controller, in 1995, I
constantly adjusted both low speed and high speed mixtures trying
to optimize mileage, to no avail. Since the 4046 was installed,
and carburetor adjusted, very little adjustment has been
required; these were small adjustments to put the closed-loop
in the center of it's range (see raw notes, above) or to change
idle speed for subjective 'feel' improvements. Please see the
carburetor selection nomograph
to select the right carburetor -- you would-be hot-rodders,
don't try to select a larger carburetor, they don't work like
venturi-based gasoline carbs.
The Model L convertor was also purchased in 1989 and tuned up
(diaphragms, valves replaced), also in 1996. It has no
adjustments.
The MSD-5 ignition I purchased in 1985 for another car; I simply
installed it on this car, originally on the old mechanical-points
distributor, then later on the replacement 1979 distributor. It has
no adjustments of any kind.
The 4046 O2 controller required one go-round of carburetor low-
and high-speed mixture adjustments at installation time. The 4046
dynamically sets the fuel/air ratio at the carburetor, so the
manual carburetor adjustments consist of setting the carburetor
slightly rich so that the 4046 can lean it out on-the-fly by
measuring tailpipe oxygen content. (It applies a modulated engine
vacuum signal to the atmospheric vent on the regulator; it can lean
the mixture but not richen it, hence the static setting is
rich.)
(September 2002: I'm embarrassed to say I just fixed a major
problem with the installation of the 4046. The 4046 modulates a
vacuum source applied to the convertor to vary the mixture; I used
manifold vacuum. WRONG! It *must* be picked off from a weaker
source, such as the recommended mixer, below the diaphragm, above
the throttle butterfly. The installation sheets are very vague
about this -- and it's critical. It worked on manifold vacuum,
though not well; symptoms were motorboating (hunting) as the
slighest "on" pulsing of the 4046's solenoid would radically lean
the mixture; the weaker vacuum source slows the loop response.)
The 1979 AMC distributor was chosen for a number of reasons,
after a lot of agonizing "research". There seems to be very little
acknowledged "science" in setting ignition timing curves; suffice
to say here, the 1979 distributor had a much more agressive advance
curve than the original distributor, which is basically what I was
after. I plotted measured distributor advance curves by hand. It
also had the advantage of being all-electronic, eliminating
annoying and hard to adjust points, and all but eliminating shaft
wear due to points-spring tension (a major source of hard-to-tune
older engines, by the way!).
To be blunt, I now consider a closed-loop fuel
system, on any car of any kind, to be entirely non-optional. I am
now quite convinced that all older carbureted, open-loop fuel
systems have essentially the same problem I had with mine,
regardless of fuel, but most people are not measuring just how
awful it really is.
Without the O2 controller, I simply could not get an optimum
mileage/performance configuration. I'd end up with good low-end
performance, but high-speed fuel consumption was terrible, or
vice-versa. Most of my research was done on the road, through
detailed and copious notes, but I also paid for four hours on a
road dynamometer in 1991 which resulted in little new data
(essentially I found less-non-optimum settings for the see-sawing
adjustments).
The closed-loop system simply solved all problems. I had a few
gyrations to go initially with optioning the carburetor, see
notes, below. Essentially, you tune
slightly rich with the loop open, eg. solenoid disconnected etc;
the 4046 leans the mixture when the O2 sensor in the exhaust says
it's rich. drops). With these settings, running open-loop,
low-speed performance is reasonably OK, high-speed performance OK
but mileage not great due to the tendency to run rich on
throttle-up and hard accelleration.
Closing the loop, by enabling the 4046, causes the Controller to
measure oxygen content at the tailpipe, through the oxygen sensor
installed there, and modulate the fuel/air ratio produced by the
carburetor by pulse-width-modulating a vacuum signal applied to the
LPG Convertor. A small solenoid quietly buzzes as it dynamically
adjusts the vacuum signal; measuring the average voltage across
this solenoid is a direct indication of the loop status; 5-10V
means the system is able to maintain the loop, with higher voltages
indicating that it's having to apply more vaccuum to lessen the
fuel to lean out the mixture; this is called the "error voltage"
because it is directly proportional to how much the controller has
to change the mixture (eg. how far is is from perfect.)
While a decent description of closed-loop servo systems doesn't
seem appropriate here, you should note that the carburetor isn't
controlled with a smoothly-varying adjustment provided by the
Controller; instead, it pulses rich/lean/rich/lean... dozens of
times per second, and measures the average result at the tailpipe.
This works just fine because the motor is a big, slow hunk of iron,
and the fuel/air mixture moving into the cylinders is also big and
slow, relative to the nimble rich/lean adjustments; the
big/slowness averages out the pulses into an effectively smooth
mixture. You will notice that the average voltage across the
solenoid varies slowly up and down somewhat; this is called
"hunting", and a small amount is quite normal. If the engine speed
"motorboats" fast and slow you've got a problem; this is covered in
the Autotronics documentation. The varying of
rich/lean/rich/lean... is called Pulse Width Modulation.
[The oxygen sensor by itself is also useful as a tuneup
indicator. Please note that it is decidedly non-linear; it CANNOT
IN ANY WAY be coerced into giving you a direct percent-oxygen
measurement! It measures one specific thing: the presence/absence
of oxygen on the hot side of the sensor, ie. inside the tailpipe,
relative to the cold (outside) side. I installed the O2 sensor a
few months before the 4046, and was able to closely set low speed
mixture by enriching until the sensor indicated no O2, then leaning
out til O2 is indicated.]
One device I found to be an utter waste of time and money was
the Autotronics 4052 LPG Ignition Recurve Computer. It essentially
recalculates a new ignition curve based solely upon engine speed,
and while it might be useful for very heavy vehicles it generally
just caused pinging on my car. It's a pain to adjust too.
The secondary effects in this area are all
good. As is well known, reciprocating engine piston rings are far
from a perfect seal; some fuel/air mixture always leaks past them,
and worsens with age. While this is true for LPG as well as
gasoline, when the cylinder walls are relatively cold, liquid fuels
condense on the sylinder walls and wash the oil film off, ruining
lubrication and vastly increasing wear. The liquid gasoline carries
with it unburnt fuel components (most visibly black carbon) which
ends up in the engine oil -- a quick glance at the dipstick on any
engine will show you the result. New engine oil, a dull yellow
color when first installed, becomes predominantly grey/black after
1000 miles or less.
While gaseous fuels also leak past the rings into the crankcase,
they do not wash oil from cylinder walls, and except for extreme
age or mechanical trouble don't generate bulk carbon, and hence the
lubricating oil stays very nearly uncontaminated. Because they are
gaseous, they are easily recirculated into the engine via the PCV
system. (Probably some trace amount of fuel is also dissolved in
the oil.)
Fact: my engine now has over 110,000 miles [Nov 98], consumes no
(zero) oil, and engine oil stays bright yellow after 4000 miles
(when I change it). I have gone as far as 8000 miles between
changes, and the oil only darkens slightly. (September 2002 note:
at 180,000 miles there is a little seeping from the rear seal; now
at 3000 miles the oil is a greyish yellow.) It seems to need the
valves rebuilt, based upon comparative annual cylinder-compression
data from 1991; as mentioned in the original edition, this engine
doesn't have hard valves, and the squirt-of-oil test seems to
indicate the dropping compression (115-125, from 140-145 in 1991
[140-130 in 2000]) is valve wear.
Oil needs to be changed regularly anyways, as the molecules
sustain shear damage and chemical changes due to heat, acid buildup
from unburnt fuel, impurities, etc.
In
1987 rebuilt my engine, from a bare machined engine block on up, in
the standard manner, and ran it on gasoline for two years/27,000
miles. In 1989 I installed this engine in the curent car, 87,000
miles on the speedometer, at which point it was converted to LPG
fuel. It now has 170,000 total miles on it [Nov98], 90,000 on LPG.
It does not seep or drip engine oil from any gaskets (except an
annoying valve-cover gasket that I poorly sealed). I believe this
to be due to the lack of gasoline and its combustion by-products, a
very active solvent, in the engine oil. I certainly didn't do
anything extrordinary when I assembled the engine.
One 'undesirable' (sic) effect is that the underchassis of my
car has rusted, because the engine oil that would normally spray
and drip under the engine is not "undercoating" the chassis. If you
think I'm exaggerating, casually examine a half dozen or so
gasoline cars over 10 years old and you'll see that their
undersides are coated with a sticky black, tarry substance made of
engine oil and road dust. Engine oil drips and mist is also the
source of the darker section or dark spots down the center of the
driving lane on roads.
These are random notes from my files over the years,
in no particular order.
1995: One on-road failure: whiel cruising at 60MPH, car suddenly acted
fuel-starved (depressed throttle, engine would 'bog', let up, depress
only slighlty, engine cruised OK; could not maintain speed). Pulling
over to the side of the road and lifting hood revealed LPG convertor
had turned into a giant snowball -- water flow ceased. I unbolted it
from inner fender (two 1/4-20 bolts), removed water access cover, about
100mL of sludge fell out. Convertor, mounted at slight angle on inner
fender, had accumulated sludge from cooling system, eventually plugging
flow. Dumping out solved on-road problem. Months later [it took a few
years to plug up, no hurry here] moved convertor, made level.
Jan 96: Convertor rebuild. Wear was reasonable; stretched diaphragms, wear
on valve faces, etc. Wax buildup. Cleaned with Dr. Bronners peppermint
soap. Rebuild took 30 minutes.
Convertor runs fine on it's side; however wax will build up instead
of running out the gas outlet. Is there a simple way to drain it?
How often? With convertor lower than carburetor, wax did puddle
insignifigantly (2-3 mm) in the bottom of the vapor hose nipple on the
convertor after many months of operation. [September 2002: this
is a false worry. Ignore it.]
CA125 throttle ass'y not symmetrical; cannot be rotated 90
degrees! However adapter Impco #A3-32 mates a CA125 mixer to a T2-4
throttle body (fits CA225) which is symetrical.
The CA125 has had the lean air dam assembly (AV1-14-4) installed since
July 1993. It adjusted reasonably well for idle and high speed operation
prior to Oxygen Computer installation. With the 4046 installed, it was
difficult to get it adjusted for both idle and high speed; idle was fairly
simple, but high speed required +2 notches rich (R) on the mixer assembly,
derived by cruising at speed (60mph), accelleration/decelleration, etc,
and adjusting the mixture control until the error voltage stayed within
range. It tended to run generally too lean, and the error voltage was
erratic. When I installed the rich airdam assembly (AV1-1447-2), I set
the mixer mixture to centered (0), and assumed I would have to repeat the
above process. The idle required only 1/4th turn leaner with AV1-1447-2
vs. AV1-14-4. When I set out to road test, I was surprised to find the
4046 error voltage stayed in range with the default mixture setting (0) --
under all conditions, including heavy accelleration (50mph up to 75mph),
except for lean-out on high speed throttle-up (same as before).
|
Home 
