An unusual misfire question

[Gavin Cooper]

I have a strange misfire problem that I cannot find a thread on anywhere else.

Every time I take my foot OFF the accelerator and coast I get multiple cylinder misfires. No misfires on acceleration and car feels great. This happens on cold starts and when warm.

VAGCOM results show:

4 Faults Found:
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 - - - Intermittent
16687 - Cylinder 3: Misfire Detected
P0303 - 35-10 - - - Intermittent
16688 - Cylinder 4: Misfire Detected
P0304 - 35-10 - - - Intermittent
16685 - Cylinder 1: Misfire Detected
P0301 - 35-10 - - - Intermittent

Usual checks have been made. Leak test done, all ok. Coils packs are one year old. All genuine. Spark plugs are new. New MAF.

I'm getting fuel pump changed next week, so hopefully it could be that. But lambda values all look ok and rich up nicely under boost. Wouldn't a dodgy fuel pump show incorrect lambda values??

Anyone else had similar problem? (I know it's a long shot!)

Cheers,
G

 

[h100vw]

I am not thinking fuel pump. That would probably cope on part throttle even if it was on it's last legs. Hitting boost would probably cause it to lean out and bog down.

Have you logged, timing pull, MAF and boost 002, 020 and 031.

The 'off throttle' bit makes me think it's not fuel.

Do you have a CAT fitted? You get pops and bangs without them.

Did it develop or just appear one day?

What are the plug gaps like?

Maybe swap the coilpack from #2 into another cylinder and see if the misfire moves.

Gavin

 

[Gavin Cooper]

I am not thinking fuel pump. That would probably cope on part throttle even if it was on it's last legs. Hitting boost would probably cause it to lean out and bog down.

Have you logged, timing pull, MAF and boost 002, 020 and 031.

The 'off throttle' bit makes me think it's not fuel.

Do you have a CAT fitted? You get pops and bangs without them.

Did it develop or just appear one day?

What are the plug gaps like?

Maybe swap the coilpack from #2 into another cylinder and see if the misfire moves.

Gavin

Thanks fore the reply Gav. It makes perfect sense if I'd just thought about it! No throttle = no fuel...hmmm...I'm obviously a little slow.

I've just had the car in to MRC who did some logs and said the car is fine.

Timing pull? Block 020? Yes this was logged and there is little or no timing retardation taking place. Which I understand is a good thing.

MAF and Boost have also been logged. MAF is maxing at 232 g/s and Boost at 1.48 Bar which, given I have standard injectors, is about right MRC said
(both figures smooth and consistent).

When I had the BT upgrade done I had a hi-flow sports CAT installed as well as the Supersprint exhaust. There is a problem currently with the exhaust - it was rubbing on the prop shaft which wore a hole through it!!! It's been fixed for now until MRC can do it properly at the weekend. However I am sometimes getting pops and bangs from my exhaust when I take my foot off the throttle.

The misfire has been happening on the old NGK standard issue plugs as well as the new ones MRC installed (side-firing ones).

As the misfire occurs across all cylinders, forgive my ignorance, but I can't see what good it would do moving coil pack number 2 to another cylinder?

Thanks for the advice. I'm going to mention the problem to MRC at the weekend and see if they can do some more investigating.

I'll post up any results.

Thanks again.
G.