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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Super lean - Help



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      05-26-2016, 11:30 PM   #1
Nonecure
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Super lean - Help

Every once in a while my car will drive like shit, and then it goes away. This time I caught it while logging. A slow cruse with just a little throttle and it goes seriously lean and runs rough. Does anyone know what is going wrong?

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      05-26-2016, 11:35 PM   #2
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Possibly a vacuum leak but it could be a few things and would have to be properly troubleshooted. Do you have a service manual?
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      05-27-2016, 11:14 AM   #3
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You may want to try changing the O2s if you don't find any vacuum leaks. Your fuel trims are flat during the lean period, so for some reason the DME isn't commanding more fuel to be added.
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      06-16-2016, 07:48 PM   #4
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Any resolution to this? My car is running pretty lean as well... Getting limp mode and 30FF. Just had the HPFP replaced, plugs, coils, walnut blast. Should be able to tackle the vacuum lines tonight but they are holding vacuum after shut down (disconnecting the clip over the intake to test) I can hear a sucking woosh
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      06-16-2016, 08:01 PM   #5
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Looks like a cylinder is shutting off, perhaps caused by a misfire. Notice your short term fuel trims are flatlined. Your bank 2 LTFT is also flatlined.

Mine used to do this and I would have to restart it, then it would be fine. Turned out to be a bad coil.

Do you have any codes? You should, judging by the log the DME knows something is wrong.

You could try swapping all injectors from one bank to the other and see if the lean bank moves too.
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      06-16-2016, 10:01 PM   #6
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Quote:
Originally Posted by 89mustaine View Post
Any resolution to this? My car is running pretty lean as well... Getting limp mode and 30FF. Just had the HPFP replaced, plugs, coils, walnut blast. Should be able to tackle the vacuum lines tonight but they are holding vacuum after shut down (disconnecting the clip over the intake to test) I can hear a sucking woosh
Normally a 30FF code is a boost leak. Mine got better after replacing the MAP sensor. Recently it had a few issues and I got a 2F0C code, so I ordered a TMAP sensor.
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      06-17-2016, 11:06 AM   #7
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Quote:
Originally Posted by Nonecure View Post
Normally a 30FF code is a boost leak. Mine got better after replacing the MAP sensor. Recently it had a few issues and I got a 2F0C code, so I ordered a TMAP sensor.
I just did some of the vacuum lines last night (didn't have enough hose) Scheduled a smoke test with my Indy next week. I haven't considered a MAP sensor issue yet but I do have a home made DCI which may have an effect. Did you ever get a code indicating the MAP?
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      06-17-2016, 12:26 PM   #8
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Quote:
Originally Posted by 89mustaine View Post
I just did some of the vacuum lines last night (didn't have enough hose) Scheduled a smoke test with my Indy next week. I haven't considered a MAP sensor issue yet but I do have a home made DCI which may have an effect. Did you ever get a code indicating the MAP?
No code to indicate the MAP sensor was messing up. Just a logical part to cause the DME to not keep the fuel ratio correct.
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      06-17-2016, 12:42 PM   #9
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Quote:
Originally Posted by 9krpmrx8 View Post
Possibly a vacuum leak but it could be a few things and would have to be properly troubleshooted. Do you have a service manual?
It's a t map set up a vacuum leak won't affect it like you are thinking it will

I'd look towards fueling hpp ECT.. There only notorius on these cars lol
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