Likely/possible causes of a misfire on one cylinder?

Faulty HT Lead?

Recently had a few VW's with single cylinder misfires & all down to the

On this car it doesn't really have HT leads. There's an ignition module containing the coils etc. that bolts directly on top of the plugs. Just four rubber things with springs inside that I'm not sure if I can detach.

Just had a thought though, tomorrow I will see if I can detach them, then swap them over and see if the misfire moves to a different cylinder.

Thanks

I would do a compression test first, solely because you mention the engine has over-revved in the past.

If thats ok, then replace the ignition cassette- they are a well known fail item.

Tim..

I bet it does. Possibly reckon they tried to get away without replacing the head or a piston.

I really do hope not. The dealer had the car for weeks (about six IIRC). I think they should've replaced the engine at the time, but we didn't push them hard enough. The (auto) gearbox on this car has

-never- been right. Even now it sometimes won't change, and pulling away it sometimes takes way too long to engage, so the driver's left at the lights etc. like a numpty.

Compression checks out ok (well, on #1 and #4 cylinders, I didn't check 'em all 'cos it's a pain)

Eurocarparts stock the module for 53 quid or so, vs. Mercedes 74 quid. I also tried breakerlink.co.uk. I got a call from a breaker this morning trying to sell me a used one for 90 quid! When I told him about Eurocarparts price he said "those guys are pirates". Erm, pot, kettle, black?

Did you check the modules yet? If it's not that then it could be injectors or the wiring or a broken rocker arm.

Avoid those breaker places they always come back with really silly prices.

My car has this arrangement and failed in the way you describe. Replacing th appropriate coil (£32) cured the problem. If you can get the coil off it may be possible to compare the input and output resistances with one of the other coils to confirm failure.

My car was a humble Fiat;-(

Another Dave

Ive COP isnt bright IMO, ive yet to see a COP setup that didnt suffer fairly regular coil failures, and fairly expensive too. Idea is nice, in practice they seem to struggle to deal with automotive environments.

Fixed!

First I checked the compression before ordering and fitting a replacement ignition module.

The Eurocarparts part was Bosch - so exactly the same as the Merc one.

Thanks all for the pointers.

Oops apologies for the repetitive info - XanaNews munged up somewhere and wasn't retrieving posts....

I cant recommend ECP highly enough - when they didnt have a "non-branded" part that i needed they gave me a =A330 more expensive genuine part without me even asking for it - it was a driveshaft that was only 40 in the first place!