Intermittent misfire on full boost

[msingh]

Good evening!!

If any of you can spare some of your knowledge and expertise it would be most appreciated.
The problem occured today for the first time. I had been driving the car on the motorway for about 1 hour, I went to overtake in 6th(aby) and it misfired, it continued to do this when ever i floored the throttle in every gear, but only as the car approached reaching full boost.
I then went to a friends garage and asked to check for any boost leaks. He found nothing.
The car was then off for about 30 minutes, i then drove home and the car was absolutley fine. It took 45 minutes to get home and did not misfire once in that time. I have since driven the car and it is fine.

I changed the plugs for the correct Bosch ones a month ago and it's been fine till now.
I have seen that people refer to POS when similar things have happened, what are these.
I have heard that the wires to the coil packs are faulty aand maybe need replacing, but my understanding was that if they were at fault the misfire would be apparent all the time.

Any help would be much appreciated..

[UrS4boy]

POSs misfire all the time when they die but wonky coils will only misfire under boost until they finally totally die. I think you have at least one dieing coil.

[iain1067]

2nd that opinion

[msingh]

Thanks for your prompt reply, should i replace all of the coils and if so what are the best options.
Once again thankyou

[blown_vr6]

Check the condition of the rubber boots that go from the coil packs down to the spark plugs, if these split they will give the symptoms you describe.

[S2central.net]

Does sound like coil packs alright... Set of 5 ain't cheap but its the only proper cure... These come with new HT leads (rubber boots if you like) but can also be bought individually if you think the ones you have are damaged.

I also wouldn't rule out the POS units either yet - worth testing with loaned spares if you want to be sure before spending almost £300 on a new set of coils.


Paul

[UrS4boy]

You don't need to replace all 5 coils if only one is gone. However, you do need to diagnose what the problem is (POS or Coil) and which POS channel or coil it is.

From my UrS4/S6 FAQ page on AudiWorld, I suggest you follow the procedure at the link below:

http://forums.audiworld.com/s4s6/msgs/149788.phtml

If it is a coil, before you decide to change it, be aware that there is a 1.8t coil pack conversion available as an alternative, either DIY (instructions available) or 034Motorsports or Apikol.

Good luck hunting this common problem down.

Dave F.

[S2central.net]

Hmmm well unless you have a very expensive multimeter / oscilliscope (and skills) its about impossible to track down which coil is faulty... And if one is bad, the others can't be long in following.

I personally don't rate the 1.8T coils either - they don't have the same heat resilience as the S2 coils. They are cheaper for two reasons - volume manufacture and lower specification.

I know it seems crazy to go and change all five coils - especially given the price - I certainly would begrudge paying the money... But the days spent tooling around trying to pinpoint it 1 at a time is just horrible... Replace all five and you'll have no more coil issues for another 120k miles (allegedly)


Paul

[UrS4boy]

Hmmm well unless you have a very expensive multimeter / oscilliscope (and skills) its about impossible to track down which coil is faulty.
Paul

Disagree strongly. Did you read the procedure I suggested in my post above? If you use an old fashioned coil tester, which tests the coil's ability to jump a given gap, you can easily track down which coil is the weakest, i.e. the one that jumps the smallest gap. Such testers are under $10 so I would think under L 5.

[blown_vr6]

As i have also said when the rubber boots split the car will misfire, i had this on my car and traced it down to a spit boot on no.4.
Do not run out and buy a set of coilpacks without checking this first.

Pete.

[merlin's S4]

Disagree strongly. Did you read the procedure I suggested in my post above? If you use an old fashioned coil tester, which tests the coil's ability to jump a given gap, you can easily track down which coil is the weakest, i.e. the one that jumps the smallest gap. Such testers are under $10 so I would think under L 5.

I managed to track down the weekest coilpack using an adjustable spark gap tester (£5 from the motor factors) but I ended up changing all 5 for piece of mind. I did the 1.8t coilpack conversion but it hasn't been without issue. Several coils from GSF have gone bad but the new ones from Vagparts have been great (touch wood!).

[UrS4boy]

... I did the 1.8t coilpack conversion but it hasn't been without issue. Several coils from GSF have gone bad but the new ones from Vagparts have been great (touch wood!).

Merlin: As a matter of interest, were the first batch of 1.8t coil packs 115 Ls and the later ones 115 Rs? I am still running 115Ls and have only had one fail in two plus years. But I am hearing good things about the 115 Rs.

Dave F.

[merlin's S4]

Yes!! I've had at least 6 fail, usually under load. 3 were replaced by GSF free of charge when I complained in the early stages of running the conversion but these have all since failed too!! Part of me wishes I'd bit the bullet and used the OEM coils but there are many advantages with the 1.8t items. They do away with the original POS's, they're easy to test for failures and very simple to change (unplug old, plug in new!) as well as being cheap and there's no guarantee that the OEM coils will last another 120k miles!!

[UrS4boy]

But have any of the failed coils been 115 Rs?

Dave F.

[Dan_s2_coupe]

I found that my rubber boot was split the othere day it had the same symptoms as u discribe but may also be a coil

i have taped the boot up for now seems fine