Misfire ???
 

Hi There,

I'm trying to get the LPG install working and struggling. On LPG I get a missfire on Cylinder 8.

I know LPG tends to show up faults in cars that petrol is less fussy with and that's what i'm thinking as it's fine on Petrol.

I've changed all the coils and all the spark plugs. I've just swapped coil and pack from 8 (back left) to 5 (front left) with no change at all.

However we've also tried running injector from 8 onto 7 & vica versa which is saying the car, but.....Well what else can cause misfires???

Vagcom codes :

P0300 Random/multiple
P0308 Cyl 8

Any ideas ???


Lee

I had this on my B6 S4, cylinder 3 at the time, kept rotating coil packs, no solution - turned out to be the inlet flap - mrc sorted that and the lpg was fine, it was a BRC system

Hi There,

Interesting. I'm guessing that there is some form of inderviduality within the flap mechanism, which means it can effect just one cylinder.

MRC ???

Thanks,
Lee

MRC are a company based in Banbury, well known for their Audi/VW tuning experience. If you are local they are worth dropping a line, if not, there are similar companies that may help and probably some local to you.

Hi there,

Peterborough Here....So it's aprox hour and a half drive....Plausible

Though I do like working on it myself!

Lee

If you clear codes and start from cold and switch to gas asap how long does it take before it flags the code , does it have the missfire counter in vcds .

Was it petrol or LPG injector you swapped?

Would not hurt to test compression and compare to other cylinders. I do have compression gauge somewhere if I can dig it out and not too far from Peterborough(~30 miles) if you wanted to borrow it.

Hi There,

I've had a look at the inlet manifold. Took the back pipe off the engine and fed a usb camera inside. Tried working the linkage and the flaps move and seem ok. I've also popped the vac pod and linkage off and cleaned those as per http://forums.quattroworld.com/a8/msgs/44689.phtml and that all seems fine. I did also take the top half off my old dead FL D2 S8 to have a look at the workings, though I understand that the 4.2 D3 A8 is a more basic manifold.
Also had her Carbon Cleaned which she idles a bit nicer and is smoother and maybe a little more responsive, but made no difference to the LPG fault - I made sure they flowed the gas through both bits of the inlet manifold too!
At which point I can't see anything wrong with the inlet, though without popping the top (and getting sealant issues as I don't think you can get a gasket) I can't be 100% sure!

I've VCDS & OBDEleven and the Zenit Pro LPG software so diag kit should be fine!

I've swapped LPG injectors and the fault stays with Cylinder 8

Running on Petrol, I ocasionally get 16804+16814 - Cat system bank 1 & 2 efficiency below threshold - I've checked the sensors via VCDS aging test and they come up below 1 and pass, though I find it odd that it's both Cat Banks at the same time!

I typically get 16684 (random) & 16692 Cylinder 8 on LPG....However the other day I also got 17718 Cylinder 10 short to ground ???

LPG needs to be warm, so you can't/shouldn't start on LPG. I can do it from warm and clear codes and you get a flashing Engine warning light. Sometimes the EPC light too. It's almost imediate.....A minute or two later you get the system erroring and cylinder 8 gets disabled, though LPG will still run on 7 cylinders.

I've noticed that high reving seems to make it a bit better, but still errors!

Lee

On the gas injector in question is there a good 12v supply and a good switching signal to it

Hi There,

Not sure how to check that, but am guessing so.

We swapped the leads and pipe (to the cylinder) from 8 to 7 and vica versa, which means the injector is fine....It certainly seems to be firing (popping).

Swapping the output and signal obviously means there is gas, however i'm not sure how to check the 12v supply. Guess leads and multimeter and see what I can find!

BTW just running some Archoil AR6400 Pro through....Doubt it'll do much, particularly after the Carbon clean, but it's supposed to be one of the best fuel cleaner additives about and may help!

Lee