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Running Like a Dog ... HELP !!!!

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Greybeard:
These words were posted yesterday in Modified under the heading LPG .....

I have a 1999 3.9 Disco on LPG and have just this week finished converting my 1990 3.9 RRC with an OMVL kit.


I have absolutely no problems at all with either vehicle. My dad runs a carb V8 on lpg and his actually starts on gas and runs very nicely. There is a minor power drop but running a V8 it isnt that noticeable. Do it, you wont regret it.


Well famous last words ... My RRC started misfiring on the way home from work and initially i thought it was running out of gas, albeit a bit too soon. It cut out at a set of traffic lights so i switched to petrol and with a little coaxing it fired up. Drove home with a little bit of a misfire but seemed to clear when i wound it up so to speak. Some time after getting home i had to go out again to pick up my daughter, car fired up ok seemed to be running fine, switched to gas, all seemed fine. As the engine reached operating temp it started to misfire again and then cutting out although it was doing the same on petrol and i had previously verified that it wasnt out of gas.
To me this seems like an electrical / fuel injection issue.
Came home tonight and checked connections , vacuum hoses etc fired her up and at first she was lumpy but then she cleared and i went for a test run thinking all was well. As the engine warmed up , the misfire got worse till i was back to cutting out again. If i keep the revs up she seems ok if they drop i have to almost feathjer the throttle in the same manner i would if it was a twin choke carb running out of fuel.
This has occurred since the sump was removed to check bottom end bearing sizes although i cannot see how it is related. For now it has me stumped , do any of you far more knowledgeable people have any ideas.
I was maybe thinking ignition amplifier or coil. one thing i have just remembered is that when i was running it on petrol it was horrendous on fuel and very rich but  seeing as it was going to be run on gas i didnt bother with it , possible cold start issue which maybe why it is worse when hot ....................

HELP

thanks in advance

Steve

500bhp:
Hi Steve, I run on gas out here in Portugal, things to consider.
The spark at the plugs has to work harder on gas as it is a "dryer" fuel then petrol, this will often highlight any problems in the HT circuit, I run with my plug gaps slightly smaller than recommended for petrol, give that a try, then give the HT circuit a good check, a trick you can try is, running the engine till it missfires then put a radio next to the engine tuned off station and listen to the static and listen out fo the tell tale clicks of a spark going to earth, or park somewhere pitch black peer in the engine bay while its mis firing and look for the little flashes on the HT circuit going to earth :D

Greybeard:
Hi Phill ,
done all that except the radio thing, thing is it does it slightly worse on petrol but is easier to keep running at low revs on petrol. Also seems smoother on gas when it was running correctly as though the engine preferred it and it was quieter.

Steve

500bhp:
Mine runs smoother on gas, it due to it being a slower burn, hence why the ignition has to be advanced on gas. I still think it sounds like a HT problem as the petol side is all off when running on gas.........also recheck any vacume, breather, hoses as when the engine is cold its running richer, when its hot it will lean off, then if there is an air leak it becomes to lean. I have the auto data cd if you want all the settings, readings, for your engine, i will need model, year engine size etc

Greybeard:
Phil

I have given it all a look see but nothing was glaringly obvious. I seem to remember there was something you could spray on your pipes and the engine revs would increase if you had a leak,cant remember any ideas ? btw i dont think it was petrol lol. I had made the mistake of fitting my coil upside down on the bulkhead forgetting they are oil filled but that was a week ago and until last night it was running superbly.
I also suspect HT side of things and if it wasnt electronic i would have said condenser.

Steve

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