Foreword
As a trained lpg installer and keen MR2 owner, it wasn’t going to be very
long before the two came together. Firstly lpg isn’t for everybody, some argue
that the MR2 should be left alone to run on petrol as it was intended and with
this I have no argument, certainly they are very economical as far as cars go
and mine returns about 35mpg on petrol. So some would say why bother? Well if
you think that out of every £50 spent on petrol £42 of that is pure tax then its
fairly obvious that an alternative fuel source is a good idea. Bearing in mind
lpg is currently 35p or so per litre its not hard to see why it should be done.
Not only that but there are other environmental issues to consider such as
engine emissions. This may seem alarmist but people are starting to clamp down
on older cars that pollute and giving incentives to those that run cleaner such
as cheaper road tax for lower cc vehicles. So it doesn’t seem too impossible
that our beloved MR2’s (and other older classics) could one day face tough taxes
or strict emission laws, and I for one want MR2 MK1’s to stay on the road. The
installation is quite easy if you are interested but it does mean sacrificing
that rear boot (is that what its called???) It was just big enough to carry golf
clubs but I don’t play golf, I could carry shopping in it but I’d rather buy a
Mini Metro for that (well it looks like a shopping trolley). So if you’re
prepared to use the boot for lpg purposes then read on…….
Preparation
Ok, to do the conversion you have to have some mechanical knowledge and be
able to drill a few holes etc. Show me an MR2 owner that hasn’t fiddled with it
and I’ll give you mine. So all of us should be able to do this. There are many
lpg kits on the market and some differ from others in a few ways but basically
they all work on the same principle and look the same give or take a valve or
screw here and there. Depending on the year of your car it may mean going for a
more eloborate system, as mine is fitted to an early 1985 AW11 with he 4a-ge
engine that has no lambda sensor. So I will presume that you have the same model
as me, although it can still be done for lambda sensored models too. A basic kit
comes as follows:-
1 tank (312mm x 600mm) which is 45 litre, but fills to 80% for safety,
meaning I get about 38 litres in it - longer tanks can be fitted but I wanted to
try to keep the weight down a bit (after all this is a sports car).
1 safety cut off solenoid – controls flow of liquid gas from tank to
vapouriser.
1 vapouriser – converts liquid gas to - well - a gas!!
1 filler valve – the place we fill it from.
1 68mm mixer – feeds gas into throttle body/inlet manifold.
various lengths of rubber heater hose, jubilee clips, T-pieces, screws etc.
First job in preparation is to strip out the boot interior and remove the
rear number plate lights and carrier. Also remove the air filter box and rubber
pipe to inlet manifold.
Installation:-
Here is the layout of components. The vapouriser is going to be placed in the
top left corner of the boot and it just so happens Mr. Toyota placed a bracket
here that it can be mounted on.
As you can see there are 3 pipes that need to reach the engine bay from here.
One of them is our gas pipe that will feed into the mixer and the other 2 are
water pipes that will be joined to the heater hoses. These keep the vapouriser
warm and stop it from icing up as the gas goes from liquid to vapour. It’s
important to keep this unit parallel to the car as it could starve the engine of
gas under hard braking if mounted transversely. A 20mm wide 70 mm long slot
needs to be cut between the boot and engine bay for these pipes and I did this
by drilling two 20 mm holes 30mm apart, and then cutting the rest away with an
angle grinder. The location of this hole is not vital but mine exits in between
the air box and n/s/r suspension top. Next cut a piece of washer pipe tube about
200mm long and slice it open along one edge - I siliconed this onto the edge of
the hole to stop the pipes chafing on the edge and also act as rust proofing.
Now attach the pipes to the vapouriser and feed them around the airbox between
the battery. The water pipes now T into the heater pipes above the gearbox using
the water T pieces provided. Mount the gas mixer onto the throttle body with the
feed pipe pointing towards the battery. A small amount of silicon helps seal
this to prevent gas loss. Now attach a 2 inch gas pipe to it and then add the
valve that controls gas flow to this. Connect the gas feed pipe from the
vapouriser to the valve. Now cut about 2 inches off the rubber hose that joins
air filter box to manifold and refit the airbox. The next job is to mount the
tank in the boot, the tank comes with a supporting frame and simply bolts onto
the boot floor with the tank being strapped to it. Orientation of the tank is
important and should be mounted with the multi valve as close to the back panel
as you can.
The safety cut off solenoid is also mounted on a handy bracket between the
tank and vapouriser. Next cut a 30mm square hole in the back panel for the
filler point making sure the number plate will cover it when in place. Refit the
number plate panel and make a hole in this too where the filler point is. Now
hinge the number plate so it opens for access - I mounted the number plate on
thin plywood and used door hinges to make it swing but I’m sure others can make
a better job of it. After the tank has been connected to the filler valve and
all pipework is secured, comes the electrics. Three solenoids need a positive
supply and an earth for them to work. One on the vapouriser, one on the tank
multi valve, and of course the safety solenoid. Earth them all to the same
place, because if you later have a problem it means you don’t have to test for
separate bad earthing points. The power supply for the solenoids is basically
what switches the system to gas from petrol and it is all controlled by a timed
cut off relay. Here is a rough diagram of the wiring
Note* although 12v ignition can be used I have used the live that feeds the
low fuel warning light on the dash so that when I switch to gas it lights up.
The timed relay works because it connects the wire from ecu to injectors as
normal when not active, it’s only when its switched on that it breaks the
injector signal wire after 2 seconds, allowing the engine a chance to get some
gas, so there is an overlap between fuels. At the same time this relay is turned
on a separate 4 pin relay is activated that turns on the gas solenoids. This
must be wired from the battery to reduce load. The switch I have fitted to
control the gas is located in the blank under the radio on the driver’s side. If
the electrical side is at all confusing please contact me and I will be able to
give any help required.
Setting up:-
Now that the gas system is in place you must take the car to a local lpg
station. Carry a selection of spanners that fit the pipe unions as I guarantee
there will be at least one that needs an extra nip. Put 1-2 litres of gas into
the tank to start with for leak checking…use washing up liquid on all the joints
and check for bubbles…if leaking tighten and test again. If no leaks are found
then switch ignition on and flick the switch to gas without the engine running,
this will open all the solenoids and fill the rest of the pipes with gas, again
check all the unions and tighten if necessary. If all the pipes are leak free
then proceed to totally fill the tank. Now to set the vehicle up on gas, fully
open both the mixture screw on the vapouriser and the valve on the gas mixer.
Start the engine on petrol and ensure it is at running temperature. Switch to
gas and see if it idles….if not then gradually screw the mixture screw in on the
vapouriser and try again. Repeat this until the engine is running on gas…even if
slightly unevenly. Once it is idling on gas screw in the mixture screw until the
engine just starts to “pink” ..it is now that you know its running slightly
weak….just screw out about one turn and it should be fairly close….this can be
checked more accurately if a local garage will let you use their gas analyzer,
if you do this aim for about 1.5-2% CO at idle. Now that the mixture is set up
the last thing you need to do is to set the valve on the mixer itself…this acts
as your fast idle volume and determines the economy of running…leave this open
fully and the engine will get lots of gas and it will be on more of a sport
setting….close it down too far and the engine will have a flat spot on
acceleration. I set mine by holding the revs at 3000 rpm and gradually screwing
it in until the engine started to falter, then opened it one turn….experimenting
with this screw over time can greatly improve the economy of the system. On my
first big outing with the gas system was actually the March run to the Lakes
with the club and I got 33mpg on lpg and did 165 miles on £8 worth of gas….very
good for its first time. After a few weeks of running the vapouriser will need
tuning again as the rubber diaphragms inside take a while to settle in with the
heat. After this setting up it will not need tuning again….unless you are
unhappy with the economy. It has to be said that it makes a very good conversion
and has increased the driving range of my MR2 by 250 miles….simply switching
back to petrol when it runs out. I hope this proves useful to other members
wishing to convert to lpg and if anyone wishes to discuss it further I will be
more than happy to help. Please email me at paulwoods.v6mr2@ukf.net
PAUL WOODS
