mikeyb

Hey guys I just bought a b5 s4 a few days ago and am having issues with boost at WOT. It is stuttering at WOT. Heres the back story. I bought it the drove it for few hundred miles then to my hometown 200+ miles away. It ran great the whole time no issues. When I got home I brought it to a self wash with a pressure wash style sprayer. I did not spray the engine bay. When I pulled out of the bay it started running funny like a misfire (shaking bad, loss of power, smelled like crap, sounded like a Subaru). I figured it was a coil or something got wet that wasn't supposed to. I parked it for a few hours and went out and started it, it ran good again so I drove it to town. When I got to town I parked it, and when I went to restart it about an hour later it ran like crap again. Turned it off waited 10 min. Started it and ran fine again. Went home then the next morning I went out and it ran like crap. I figured it would be a coil issue so I checked the coils by unplugging one at a time seeing what ones changed the idle. I found out that looking at the motor the cylinders on the left side were having problems the top cylinder didn't change idle bottom changed it a little. I replaced the top cylinder coil and it ran a little better. but still shaking and sounded like a Subaru. So I went to the next thing maybe fouled plug? I replaced the plugs with iridium plugs. no change. after that I guessed ICM. I couldn't get the ICM anywhere from parts stores so I went to a salvage yard and got them off of a A6 with the 2.7tt. (same part numbers) After I changed them the car ran great again but then started to boost funny. Like I said it stutters. It dosnt feel like its getting full boost either on some of the pulls. It only happens when you come into boost hard under heavy acceleration. Idk what to try next any info would be great thanks guys!

Prospeeder

You need to get a OBD2 scan tool and clear the faults, and then drive it, then recheck. It will tell you whats misfiring or happening. I have seen worn or too wide of gaped spark plugs cause issues at high boost. Pulling the connectors on the coils while its running can damage them from current spike. Not the right way to diagnose newer cars with misfire detection.

mikeyb

how do you check coils then?

G_claudz

It can be really difficult to check blown coils, even when scanning the car, the faults sometimes wont surface up. I recently blew a coil or two on my 1.8T and it had the same symptoms where it would drive fine when not boosting but under load it would miss badly and VCDS did not pick the error up, I replaced all the coils and that solved the problem. The best way to rule out your coils is either buy new ones which can be costly or get someone else with the same car and try their coils. Prospeeder is correct in saying that the gap on your plugs can also cause the car to jerk so I would double check that too. from my understanding of your situation, it sounds like your coils have had better days.

Prospeeder

If your using vag com you can watch misfire monitor and see which ones are missing under load.

mikeyb

okay only code that its throwing right now is cylinder 4 misfire. I replaced coil and maf..... still studders under boost and when I start to boost harder my cel starts to flash

mikeyb

hey guys fixed my problem. DAMN PLUG GAPPING!!!! I had bought a set of autolite iridium plugs and never gapped them. After a lot of reading I found that the plugs I bought are junk and should never be put in a car lol. I bought new ngk bkr's and gapped them to .028 and she runs great now! after putting in 2 new coils icms and injectors..... gotta learn somehow I guess the easiest route first next time.