Stutter at high revs under acceleration

[alijames]

Hi All,

Just noticed a repeatable stutter for the first time today, which only happens above 5k when accelerating hard. The engine seems to misfire and stutter until I change gear, then we are off towards the horizon again, smoothly until we hit around 5k again. Checked it again several times, and it only happens under full throttle acceleration.

No fault codes logged in VAG-COM, and I don't seem to be down on power. She is not mapped, and fuel economy is about 32mpg which is normal for me, as most of the time I drvie like I have Miss Daisy in the back! Just the odd squirt of throttle to overtake rodents...

I'll have a look for obvious boost leaks tomorrow and try and get some boost logs if I get time, but any other suggestions welcome.

Cheers,

 

[s3dave]

The only thing i can think off is coil packs breaking down under full load, or sparkplug change?

 

[<tuffty/>]

Sounds like a coil pack issue to me... had an S3 in the other week with similar issues... the guy had bought brand new (from GSF) bolt down coil packs and one was failing under load... drove fine off boost/low rpm...

As Dave said though, check your plug gaps (should be 0.8mm on std engine, 0.7mm if mapped) or even change the plugs if you haven't for a while and see what happens but I suspect its like Dave said.... coil pack breaking down...

Buy Genuine when you replace them or see if you can get them replaced as part of the recent recall from Audi...

<tuffty/>

 

[alijames]

Thanks for the thoughts guys. No sign of coil packs ever being changed in the service history, and I have not done it in the 30k I've done, so sounds a good place to start. I'll have a chat with Oxford Audi about the warranty replacement...

Cheers,

 

[s3 Hoggy]

Had exactly the same issue mate, nothing come up on vcds to start with but it slowly got worse then the EML come on for a few seconds. Plugged it in and had a misfire on cylinder 4, replaced coilpack which fixed my problem.
Was at Oxford Audi 3 weeks ago to get some parts and they wanted to book me in to get the coils replaced but didn't bother as I have all 4 latest coils fitted anyway

 

[alijames]

That's good news Hogster.

Cheers,

 

[beachbuggy]

If a coilpack has/is failing then it will be high on emmisions, you could take it down to a friendly MOT'er and get them to do a gas analyse on the car and if it's high on C02 and the lambda then it'll be a faulty Coilpack.

Other than that I would also suggest checking the vacuum/boost pipe to the fuel pressure regulator, if that's got a leak then the fuel pressure wont rise with boost and you'll get a misfire/bad running.

 

[richieb138]

If a coilpack has/is failing then it will be high on emmisions, you could take it down to a friendly MOT'er and get them to do a gas analyse on the car and if it's high on C02 and the lambda then it'll be a faulty Coilpack.
.

I had a very similar sounding issue which appears to have gone after a coilpack replacement, although it wasn't very repeatable, it was quite intermittent (i.e. it had good and bad days).

Mine passed an MOT with the bad coil installed (and no related advisory or anything), so I don't know how much of an increase on CO2 to look for to be diagnostic?

As mentioned above, check out the free coilpack recall at Audi to see if you're covered, that would be an easy way to rule them out

 

[s3dave]

If its failing under load, there would be no reason it would fail the emissions on idle or fast idle, as the engine is still not under load....

 

[beachbuggy]

Recently MOT'd a car that failed the MOT due to high emissons. Ran fine but had a slight stutter at around 4500rpm. The CO2 reading was 1.30 when limit is .30 and the lambda was around .90. Car ran fine otherwise even at fast idle for the mot run.

Isolated it to a coil pack which was changed and the emissions went straight down to 0.02 and lambda at .97 which is bang on.

I agree if it's failing under load then it shouldn't affect fast idle, however from personal experience I can vouch that it can and has so I learnt something that day.