BMW 740i LPG Problems

[Remagel2507]

Hi

I have posted this in the GG forum instead of BMW because of the nature of the problem and it may not be specific to BMW.

Anyway I've been having a few problems with my 7 at the moment, the first problem was a serious misfire which occured after I carried out a major service, during the misfire the engine ran both on petrol and LPG. I decided to do a compression test after a diagnostic test revealed nothing.

Whilst doing the test I noticed that one of the spark plugs had a bent electrode once straightend I put them all back in, fired it up and it ran perfectly. A quick blast up the road showed a massive improvement in performance, however now when the engine warms up the controller starts bleeping and flashing which according the manual means that the tank is empty - I know the tank is not empty because I filled it right up recently and have only used the car once as it seems to be gulping the petrol.

I ordered a LPG diagnostic kit of ebay but the damn thing wont work because apparently the controller needs older software????

Also worth mentioning that Ive changed both lambda sensors and cleaned the coil packs as it failed its MOT on emmissions

I would appriciate it if someone could help me on this because its getting annoying now not being able to use the LPG.

LPG kit is a STAG-300-8

Many Thanks

[rallycross]

Obviously the first thing is does the car run fine on petrol, or is it just lpg where you have a problem. Once running fine on petrol (check all the usual things leads coil packs etc) then sort out the lpg.

The older lpg systems are very sensitive to changes, eg a service and change of plugs can result in misifre and lpg running problems, i've no idea why this happens.

NGK plugs are supposed to be the best for lpg cars is that you have fitted? I recently changed plugs to new nkg plugs and it then caused a misfire (was running fine before) so I put the old plugs back in and it was fine.

My local lpg service guy has said to me if an older car is running fine on lpg better just leave it alone than risk upsetting it.

[Remagel2507]

It runs fine on petrol, but weirdly since it has been running better on petrol I get a problem with the LPG I'm wondering if I disconnect one of the coil packs and see what happens

[Bungleaio]

Have you gapped your plugs correctly? LPG requires a smaller gap in order to work correctly.

I was having a couple of issues with my impreza switching over to petrol when pressing on but I'm now running these http://www.ngk.de/LPG_LaserLine.4629.0.html The LPG fitter was a bit sceptical of them but my car is running great now. It will still switch back to petrol if it gets over 5500 revs but I can live with that.