G'day guys,

I've got 5 speed V8 EF mont on gas that's the slowest thing on the road and has been giving me grief in some way or another its whole life. I love it. Newest challenge is cutting out whenever I accelerate with a bit of haste. Pulls fine when on petrol though!

Short version: Anyone recommend a decent LPG mechanic familiar with IMPCO systems on 8's in the western suburb sort of area?

Thanks!

-Justin



Long version:

I'm typing this entirely from memory and know nothing about LPG really so forgive my vagueness.
IMPCO gas system. PEEL controlly box in the engine bay, IMPCO box (Gas ECU? There's wires running to the O2 sensors) under the dash and another box that I think solely controls the fuel changeover? There's also another wire running from the IMPCO box that goes to the actual EEC ECU but I think that might be solely so the dash petrol gauge also swaps when you switch fuels.

It only really does it while under load and only thru about 2-3 grand. If you gradually accelerate its ok, no hassles, as long as you're in first. Try and put the boot in a little and actually get the heavy bastard to move in 2nd or 3rd and it doesn't really shudder so much as 'oh god leaning out like someone cut the gas line'.

Leads? Coil? But it doesn't seem to do it on petrol. It does idle like a b**ch though, I'll get round to that. Idle is fine on gas at around 900ish, its just on petrol after a while the ecu decides it wants to idle closer to 600 and then it hunts.

I can post a video, but it doesn't really do it while stationary. The royal melbourne show is on at the moment, I live right across the road from it. I sit and watch cops pull people over alllllll day and I don't particularly want a canary for just going around the block.

Possibly relevant information:

I do not know any good LPG mechanics in this area. Also, between this car and a project car I am poor in both time and finances at the moment. 500 bucks and a weekend of labour replacing parts that are still serviceable seems wasteful. In saying that, I'd gladly pay someone to tune, find and fix the problem. But I am a little hesitant about mechanics I don't know and would simultaneously feel guilty burdening my 'trainwreck on wheels' to any poor old bastard.

The car was sitting for two years with a busted engine mount, I only just had them replaced. The car HAD done this to me once or twice beforehand, but now its a regular thing. I know that at some point the mixer was removed from the car in order to get the engine out. I do not know if correct sealants were used when refitting it. Soapy water test seemed all ok, but that's hardly a proper pressure test now innit.

I also put on a set of EL GT extractors while the engine was out, they were from a car that drove beautifully so O2 sensors probably good. Yes I reset the ECU. Plugs looked good, gapped correctly.

The mixer has in the past blocked up and froze on me, this was like 3 years ago. I'm pretty sure the coolant hose just split, I mean I fixed it within the day, but I can't remember for sure.

So many words, so little useful information!

I was about to say that the symptoms are very similar to icing up as well!. Do you have good water flow? -Are you sure the O2's are ok? - Petrol will work ok-ish with bad sensors, LPG often not.

The EB GT Extractors will have changed the cars air flow characteristics. You probably are going lean, and before the Peel ECU can correct for it. Unfortunately Ive never owned a controlled Impco setup - always the other style and I can deal with those

Nigel

Cheers for the reply Nigel!

Didn't get much time over the weekend to have a prod about, should do later today though. I'll go over the hoses and test the oxygen sensors properly with a multimeter. The sensors came off an EL XR8 II with low k's that ran quite nicely, buuut that's probably more like quite nicely when compared to my car haha.

I did find this with a bit of googling
http://documents.rasoenterprises.com/Impco/PPI-38.pdf



Lookin like I might not have a choice about paying a visit to a gas specialist!

Are you definetly using Impco ECU's, or are you using one of the aftermarket Gastec or Peel ECU/Controllers?

I'll double check and get the proper model numbers, I'm 99% certain it's an impco commander inside under the dash. Just checking the PEEL website, their base model processor looks an awful lot similar to their injector and o2 emulator unit. Being in the engine bay, I'm gonna guess it's the latter

http://www.peelinstruments.com.au/page13.html

Hmm, am I getting ahead of myself in assuming that extractors + impco ecu getting a reading from the emulator and not the oxygen sensors themselves might lean things out a touch?

Way ahead of yourself.

The Emulators are for the petrol ECU while on LPG.... not LPG Ecu.

Worth visiting an LPG Guy still

Right, I follow ya. Just a tad excitable when I think I might be on to something

Multimeter on the oxy sensors showed about was expected, ill bench torch and test the other two to see if they're any better.
Hoses all good, solid connections and no kinks.

Engine bay PEEL unit... the safety switch... durrrr
Impco Commander Oz, got that part right, still need the fuel system analyzer to tune it. Time to find and visit a decent LPG bloke.

Appreciate the help mate!

just read your post, cutting out under fast accel , do you still have a broken engine mount. my car would pull the vapour hose off the convertor under hard accel, and would slip back on when u backed off. also filter on the gas lock b4 convertor may be blocked, this will limit power. gas cars will pull hard until the mixture leans out, then they just fall on their face. lean out can be b4 or after convertor, even down to the tank tap not being fully on. the wire on the impco box going to your ecu is oxy sensor or throttle position switch. petrol cars run rich or lean till they wont start or run. gas is exactly the same except the "window" between too rich and too lean is much smaller. so "x" amount of lpg vapour from your convertor will allow the engine to run to say 3500 rpm, then "y" (a bit more) will let it rev to say 4500 rpm. both time the car will accelerate well, till it hits the respective rpm. then its like your driving through dry sand.

Cheers for the reply dude, sorry for the delay in any sort of update.

Engine mount is most definitely not broken, have checked and re-checked. Also replaced the vapour hose and water pump hoses just for safe measure.

Otherwise that makes a hell of a lot of sense and may well be most of what was happening. With checking the IMPCO to the ECU wiring in relation to a bunch of wiring diagrams I stumbled upon, and along with your description of the tiny margin of error between "weeeee" and "whoops drove into mud", it seems spot on.

I did end up taking it to an LPG mechanic for a check. Apart from being informed that I need to have the tank properly pressure tested and to have all the connections re-re-re-checked, I was told to simply run a few more tanks of both petrol and LPG thru the car. So far so good, there's definitely been an improvement on the LPG side of things, the cutting out is almost entirely gone. But if I have been running on petrol then the acceleration issues startup again when running on LPG (though not nearly as badly) and occasionally the car will stall when coming to a stop.

From how it's been behaving I've been told to bump the base idle up slightly, but if that doesn't work, then the only option seems to be a dual tune with a J3 chip. Don't get me wrong, after a month of regular driving there's a whole world of difference now compared to how it was, but it's still... questionable at times.

Thanks again for the help guys