GQ losing power on LPG

[A*D*A*M]

My '92 injected petrol GQ has started intermittently losing power on LPG. Doesn't do it when running on petrol. Only does it under load after about 10-20 secs of having foot down (ie going up hills). Seems to run out of gas and just gets slower and slower, even when I crest the hill and car is no longer under load. Problem stops immediately when I switch over to Petrol and power comes back. When I switch back to LPG after that, all goes fine (until I load it up again).

I have fitted new air filter (and tried said hill without filter fitted), same issue. Gas mechanic has tested gas flow, fitted new gas filter and has apparently adjusted about every thing that can be adjusted. Conducted full tune, timing, plugs and leads are fine.

Car drives great around town and gets along well from the lights but as soon as I load it up for a bit of an extended time, it just seems to run out of gas.

Impco LPG system is fairly new, about 12 months and 25,000km old, and the problem has only started in the last month or so. I can't see any kinks or blockages in gas hose from tank to mixer.

So far it has cost me a fair bit in labour for mechanic to mess around with everything without actually being able to identify anything wrong. He suggests re-building the condenser and mixer next (I don't know price yet but I imagine it won't be cheap).

Has anyone experienced anything like this or have any advice on what might be causing the loss of power/gas?

Any help is hugely appreciated.

Adam.

[bodes-sh]

do these motors run an o2 sensor? how many km has the actual car done? the gas converter and mixer won't need a rebuild after 2 months, the only thing I can think of to begin with is the lpg processor (if the vehicle runs an o2 sensor, pretty sure they do...) thinks the mixture is too rich and is closing the stepper motor down, resulting in lean out and lack of power. do you know what mixer is on it? some of these run a vacuum controlled diaphragm which lifts up or lowers down depending on which fuel you are running on. if you have a vacuum leak or a loss of vacuum the diaphragm may be moving, causing lean out on lpg...

if you can, go back to the installer, if he has the diagnostic equipment, and either take him for a drive with the diagnostics hooked up or leave it with them and get them to have a look at it. it may be better if you take him, at least then you can tell him when the problem is occuring. he should be able to diagnose it and tell you what needs doing to fix it...if he is any good that is...

[ANDREWGQ 351]

Gas converters can become blocked or strick and not open completely. this would affect converted gas flow on a high demand situation like going up hills at full throttel.
the converter may need a rebuild, although a new one may be cheaper, i would not touch the mixer yet as they do not normally give problems

[A*D*A*M]

Thanks for the info Guys.

bodes-sh
Car has about 193,000km on the clock. Is the O2 sensor part of the air flow meter (in which case, yes it has one) or is it in the LPG plumbing?

I guess it could be a vacuum issue, I'm not 100% sure all the vacuum lines are in the correct spot. I had to drive to Sydney to get the original conversion done due to extended waiting lists in Canberra at the time. The guy who did the orig job didn't do a really neat job (wires constantly seperating at the connections, vacuum lines too short and pulling off their nipples, no heat shielding between exhaust and gas system, 2nd hand gas hoses used, petrol hoses kinked and squashed, the list goes on. I guess I should have taken it back to Sydney to get it all fixed properly under "warranty" but we were already having other issues after he dropped my car off the hoist as he was doing the initial work and had a particularly bodgy body job done to fix the damage. Needles to say, I don't recommend the "Gas Man" in Sydney to all my friends (rant off)).

Anyway, I got ripped off, but after paying to get initial issues fixed the car has been running fine for about 12 months. I have taken it to a gas specialist and was kind of hoping he may be able to diagnose the problem, but no luck as yet. He's had the car for about 5 days over about 3 weeks.

Dumb ass question coming up. Is the mixer the bit that is plumbed in to the air intake (I guess to mix the gas into the air flow)? Assuming this is so, then that the converter is the other bit that the gas line first goes into? Mixer is Impco C1-18 200 (?) part no. 200M-2-2, Converter is LB-2 Model L Part no. 700419 as printed on each bit.

ANDREWGQ 351
Is there a way to isolate whether it is the converter that is causing the issues, without going to the expense of buying another? Is it normal for a converter to pack it in after only 12 months (although after what I've described above, there are no guarantees that I was given new parts)?

Thanks for the advice you've already given and any more ideas you may have.

Adam.

[bodes-sh]

o2 sensor would be in the exhaust manifold, should have a large wire going into a metal spark plug looking thing. possible 2 - 4 smaller wires connecting into the end of it. has the mechanic witnessed the problem? if he knows what is happening he should know what to do to fix it, whether it be a tuning issue or needing a new converter. has it only just recently been doing this, or has it been happening for a while?

just another thought, how long has it been since you had the cooling system serviced and where does the temperature gauge sit on the dash when going up these hills? if the thermostat is not working properly, the coolant is low or there is a blockage in the system somewhere the converter may be freezing, which will cause loss of power and stalling too because it gets too cold.

[PGS 4WD]

Does it run (idle) crap straight after loosing power?? If so could be a plumbing issue, converter dropping in temperature under heavy load for a period. Could also be if the system is trying to run in closed loop under full power, there is a bleed that can be opened up slightly on the closed loop bleed system that is usually on the lid of the converter, but do so gradually or you will loose closed loop control and have difficulty getting the cruise mixtures correct. It really shouldn't be hard to find on a chassis dyno.

Cheers

Joel

[JeSTeROCK]

I've got the same problem

93 EFI Impco

When i get a chance i'll take it to my mates dyno to test closed loop theory

The air flow light (blocked filter) comes up on my dash

[ANDREWGQ 351]

Adam, I dont have experience using or tuning closed loop systems as i have never had them, however you can get a good idea wheather its the converter or the mixer that is giving you trouble by this test.

This assumes that the system is leaning out really fast and thats where the loss of power comes from.
First ensure that the air filter is clean.
Note where the high speed mixture screw on the mixer is set and turn it to allow full flow. after the test it can be put back
Do test runs in 2nd or third gear, (you need to be able to hold a load at full throttel and high rpm's for a while)
Test
in 2nd gear start progressively accelerating from 2000rpm through to near 4000rpm.
if this is ok then repeat but acelerate at a faster rate.
if 2nd gear is ok with fast acceleration then go through 2nd into 3rd and continue test

dont hold the pedal on the floor just add more throttel as the enging can use it.

if the converter is not supplying enough converted gas then it will die at high rpm as the engine is getting lots of air and no gas.

If the mixer is blocked then it should be down on power all the time as the engine is not able to get enough air or gas