[Varjo]

I've been having an increasingly noticeable issue with my engine. When it is cold, it often (but not always) runs a bit roughly. Sometimes shakes slightly at idle and is very surgey and jerky at low speeds when cold.

When warmed up, the low speed and idle behavior is much better but I occasionally feel hesitation or stutter at WOT. Sometimes the car starts vibrating and not really accelerating. Other times it pulls strongly. This has been going on for a while and does not seem dependent on where I fuel up.

No check engine light, but I did find a 2E90 fuel mixture code last week as well as two shadow "super knock" codes. They have not reoccurred since I cleared them.

I have taken a log here: http://www.datazap.me/u/varjo/novemb...=0&data=3-5-23

To my untrained eye stuff doesn't look too bad. I have a few thoughts:

1) My LPFP and HPFP look healthy
2) Fuel trims are a bit negative, fuel injectors?
3) Some timing corrections, but it doesn't look too bad here (as I said, the issue seems to be intermittent).
4) I am slightly under boost target. Is this normal or does it look like a boost leak?


I want to avoid paying over a grand to swap all injectors if that isn't needed (of course if it is the issue, I will gladly pay to have it fixed).

The car has new plugs as of 8k miles ago as well as a carbon clean, but the ignition coils and injectors are original (car is a 2008 with 70k miles). The HPFP and LPFP are also original and to my knowledge VANOS solenoids are as well.

Any help would be hugely appreciated. I'm getting pretty frustrated... I love this car when it runs right but man is it finicky.

[Sgop335]

#4 is not normal and there may be a BL. Check obvious places - ic, cp connections etc. to be tight. Iats are going up pretty good, stock?

Ignition coils worth changing at 70k, relatively cheap and easy.

[klipse]

You don't get any recurring misfire codes with the hesitation/jerking?

[Varjo]

Originally Posted by Sgop335

#4 is not normal and there may be a BL. Check obvious places - ic, cp connections etc. to be tight. Iats are going up pretty good, stock?

Ignition coils worth changing at 70k, relatively cheap and easy.

Thanks for the tip on the coils; I'll look into it. As for the boost, so the logs look abnormal to you in terms of boost vs target boost? I'll go check connections (still stock chargepipe so that's my first suspicion). As for IATs, yeah I'm stock. I only run 1+ once it gets cooler around here (but the behavior persists on other maps).

Originally Posted by klipse

You don't get any recurring misfire codes with the hesitation/jerking?

Never seen any misfire codes, just the "Super Knock" ones the one time (they were inactive by the time I saw them) and the 2E90 Fuel Mixture code.

[Sgop335]

Originally Posted by Varjo

Thanks for the tip on the coils; I'll look into it. As for the boost, so the logs look abnormal to you in terms of boost vs target boost? I'll go check connections (still stock chargepipe so that's my first suspicion). As for IATs, yeah I'm stock. I only run 1+ once it gets cooler around here (but the behavior persists on other maps).




Never seen any misfire codes, just the "Super Knock" ones the one time (they were inactive by the time I saw them) and the 2E90 Fuel Mixture code.

Leaky vacuum lines can do it as well. There are many posts here on replacing vacuum lines w silicone ones.

[Varjo]

Originally Posted by Sgop335

Leaky vacuum lines can do it as well. There are many posts here on replacing vacuum lines w silicone ones.

Interesting; I'd never heard of this. Could my slight boost leak also cause this? At low throttle when the car is pulling intake vacuum, a boost leak could result in additional unmeasured air entering the engine right?

[YoungBlood]

Ignition coils, or a MOSFET about to give up the ghost is my guess. I had similar symptoms, a stutter under load (like getting into boost up a hill, or passing) As for being under target, I'd agree that not being able to hit initial target is a definite sign of a boost leak. However, almost every n54 around here (5000-6000 ft of elevation)I know of is under target in the upper rpms. Another thing, is with the v7 maps, I much prefer linear throttle. These cars spool so fast, that with an aggressive throttle map and high boost, it can be a bit like an on/off switch, especially if you're wastegates are closed off throttle, these little snails will make a psi or two of boost even when the DME isn't calling for any yet, at least that's been my experience. Try linear throttle mapping, swap all your coils, and try to find that boost leak

[Varjo]

Originally Posted by YoungBlood

Ignition coils, or a MOSFET about to give up the ghost is my guess. I had similar symptoms, a stutter under load (like getting into boost up a hill, or passing) As for being under target, I'd agree that not being able to hit initial target is a definite sign of a boost leak. However, almost every n54 around here (5000-6000 ft of elevation)I know of is under target in the upper rpms. Another thing, is with the v7 maps, I much prefer linear throttle. These cars spool so fast, that with an aggressive throttle map and high boost, it can be a bit like an on/off switch, especially if you're wastegates are closed off throttle, these little snails will make a psi or two of boost even when the DME isn't calling for any yet, at least that's been my experience. Try linear throttle mapping, swap all your coils, and try to find that boost leak

Thanks for the tip. I actually am on linear throttle (and totally agree, it's a big improvement). I'll hunt for the leak and look into the coils and vacuum lines (as someone else suggested) before I go full panic mode and start buying injectors.

[DE92an]

at one point i see your bank 1 injectors at 140 and your bank 2 at 234 (closed) it would seem your bank one is leaking a bit actually looking at it there is a few times your bank one is about 10 to 30 psi different then bank 2. I just went through this a month ago changed all plugs, coils and vacuum lines I have a stg 2 fuel pump new hpfp this problem didn't go away until i changes my injectors I had the same slow reaction in bank 1 as yours now its been running like a brand new car.

[Varjo]

Originally Posted by DE92an

at one point i see your bank 1 injectors at 140 and your bank 2 at 234 (closed) it would seem your bank one is leaking a bit actually looking at it there is a few times your bank one is about 10 to 30 psi different then bank 2. I just went through this a month ago changed all plugs, coils and vacuum lines I have a stg 2 fuel pump new hpfp this problem didn't go away until i changes my injectors I had the same slow reaction in bank 1 as yours now its been running like a brand new car.

Hmm, I don't actually an injector field in the logs. What parameter are you looking at? This seems like unfortunate news on the injector front though.

[DE92an]

Originally Posted by Varjo

Hmm, I don't actually an injector field in the logs. What parameter are you looking at? This seems like unfortunate news on the injector front though.

Lambda 1 and Lambda 2 will tell you if your injectors are leaking once you let of your gas they should both be showing 235 that's one way to see if they are leaking, or you could park the car and pull plugs and see if they are soaked in fuel but to me it looks like one of your injectors in bank 1 is leaking

[Captain Canuck]

Try adding a bottle of BMW or Redline fuel system cleaner. It won't cure all your issues but I've found using it every 5000 km makes my idle (especially at cold temps) smoother.