Mystery miss from hell...

[elijahallen]

Hey guys, I am a B8 S4 owner and have a friend that I talked into buying a 09 B8 A4 with 75K miles on it and it developed a miss early on in her ownership and we can not for the life of us figure it out. So far we have done the obvious things like new plug and coils and a carbon clean. The miss is mostly at idle or very low rpm. There is also a mystery rattle that seems to be coming from the upper back of the engine, not sure if they are connected or not. Does anyone have any ideas that we could check? Thank you for any help.

Elijah

[elscotto80]

Start with a scan and post the fault codes.

[elijahallen]

Scan shows #3 coil pack but we put new ones in.

[audinutt]

The rattle sounds concerns me.. Sounds line timing chain guides are toast

Sent from my SM-N900V using Tapatalk

[richardm0025]

Carbon clean fixed my low rpm missfire, try that?


Sent from my iPhone using Tapatalk

[elijahallen]

Carbon clean was done.

- - - Updated - - -

The rattle worked concern me.. Sounds line timing chain guides are toast

Sent from my SM-N900V using Tapatalk

If timing was off wouldn't it throw a code?

[pierreb]

My cyl2 misfire with similar symptoms was only fixed by replacing the cyl head. We suspect the original chain tensioner had caused issues even if it hadn't actually skipped timing. It's also possible that if you get a bad enough carbon issue it could prevent valves from spinning properly. Another thing to check is the wiring continuity to the cam solenoid.

[elijahallen]

My cyl2 misfire with similar symptoms was only fixed by replacing the cyl head. We suspect the original chain tensioner had caused issues even if it hadn't actually skipped timing. It's also possible that if you get a bad enough carbon issue it could prevent valves from spinning properly. Another thing to check is the wiring continuity to the cam solenoid.

Ugh, this is my fear, running out of other options.

[mahunik]

Rattle could be typical wastegates on these cars. i got it good

[elijahallen]

[QUOTE=mahunik;11922454]Rattle could be typical wastegates on these cars. i got it good[/QUOTE

Does it rattle just idling? Any vids of the sound? Thanks

[tjaudi]

Did you fix this, having same issue with cyl 3 mine is a 2.0 T and the missfire gets to like 10 every 1k


Sent from my iPhone using Audizine

[tjaudi]

Did the plugs and coil, same thing. Didnt do the carbon clean


Sent from my iPhone using Audizine

[mecg]

Leaky fuel injector?

[tjaudi]

Would a leaky fuel injector throw a code in vcds?


Sent from my iPhone using Audizine

[pierreb]

Would a leaky fuel injector throw a code in vcds?


Sent from my iPhone using Audizine

My leaky injectors never did before they were all replaced. They do sometimes cause misfires I think. They were warranties to 120k miles. Depends on the leak maybe.

[jfo]

I chased an engine vibration for months that was inconsistent and only happened under certain driving conditions. No codes were set and I assumed it was something mechanical like a mount. Finally when a very strong shudder happened it set a misfire code in cylinder 2. It was coded as intermittent and unconfirmed, clearing itself after a number of driving cycles and before I could get the dealer to capture it on their reader. By now I had replaced plugs and coil packs and we all thought it was pointing to an injector. I could not get the code to remain set long enough to get it to the dealer and done under warranty, so just replaced it a few days ago myself. Problem is gone. I don't know if it was clogged, leaky or something else in the injector.
So, a bad injector can cause misfires and not set any codes at all.

[Alex1188]

Did you fix this, having same issue with cyl 3 mine is a 2.0 T and the missfire gets to like 10 every 1k


Sent from my iPhone using Audizine

What year car and any mods?

[tjaudi]

2009 a4 quattro trip, stock.


Sent from my iPhone using Audizine

[tjaudi]

So im going to try to swap injectors to see. Ill let you know


Sent from my iPhone using Audizine

[tjaudi]

Found issue, did vagcom and it didnt throw error but measuring values showed the missfires in Cyl 3 so replaced coil, plug but no go, vagcom still showed the misfires on cyl 3. And it was apparent because you could feel the missfires. Pulled all the coils and all the plugs and noticed plug 4 had a bent/broken electrode. So i replaced that plug and tested again, and no more missfires. So im stumped why vag showed cyl 3 but in reality was cyl 4. Weird, either way im happy now, car working.


Sent from my iPhone using Audizine

[pierreb]

Glad you solved but if the electrode is truly broken then it's floating around somewhere...

[tjaudi]

Yeah your right, i have the spark it's bent


Sent from my iPhone using Audizine