Misfire please help :( (no engine light, no codes on VAG)

[abc123]

hello friends i have a noggy blue audi s3, 2000 plate, revo'd and forge dv007p (or something)....

my car started misfiring whilst i was driving on the motorway, no engine management light, misfire only under load... when accelerating hard. anyways took it to a local garage.... said it could be spark plugs replaced with ngk platinum - drove perfect for 5 minutes and started misfiring again....

did a bit of research, so unplugged the MAF, made no difference. took it back to the garage 3 errors on VAG-com - MAF, Secondary Air Injection Incorrect Flow (P0411), Boost Pressure Control Valve (N249): Open Circuit.... anyways garage fixed all these errors (replaced MAF) and cleared on VAG-com... drove home again started driving ok for 2minutes but under load started misfiring....

took it back to garage, NO errors on VAG now, looked at coil packs - cylinder 3 small crack, 3rd cylinder (new) spark plug - carbon fouled (dry, soot, black), replace spark plug - worked perfect for 5 mins but started misfiring again.

1. if the coil pack was faulty it would have shown on vag or engine management light would be on? (i have none) (yes engine management light works)

2. spark plug keeps fouling only on cylinder 3? (my car does need a service, what else could i check for this - fuel filter, air filter, o2 sensor etc please help)

thankyou

 

[S3 HODGE]

Its highly likely the Coilpacks...Very common problem on the S3's.

Maybe a good idea to bite the bullet buy all four at once as they tend to all go slowly after each other

 

[Welly]

did a bit of research, so unplugged the MAF, made no difference. took it back to the garage 3 errors on VAG-com - MAF, Secondary Air Injection Incorrect Flow (P0411), Boost Pressure Control Valve (N249): Open Circuit.... anyways garage fixed all these errors (replaced MAF)

Hi mate, bit concerned that they replaced the MAF based on the fault code for it. I expect the reason it came up with a fault for the MAF was because you unplugged it. This would of brought a code up saying MAF signal too low...

Misfires don't always log in VAG COM, I had one only yesterday which didn't.

If I was you, since the plugs have been changed, i'd get a replacement coil pack (just one) and work through the cylinders 1-4. If it's a coil, it will be one of them... Once you have identified which one it is, at least you have a working motor, then buy replacements for the other cyls as Hodge said.

 

[Welly]

And if you're having problems with cyl 3, that would be the place to start....

 

[S3 HODGE]

O yea if its fouling on cyl 3 you may find that cyl 1 will play up aswell

 

[abc123]

But would a faulty coil pack cause a spark plug to foul? and two different vag computers havnt picked up an error now, I though a faulty coil pack would have shown on vag

 

[Welly]

Well, it depends what you mean by foul.... can you elaborate mate?

 

[Broken Byzan]

If the coil pack is borderline, it will not throw a code. Replace coil pack 3 and try again.

PS do not be tempted to use a pattern part, get the original from the stealer, £3 extra for peace of mind