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      03-19-2017, 08:44 AM   #1
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Drives: 2009 135i | https://bmw135iblo
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Fuel Trim HELP- lean code

I have a 135i(N54) ST2+ with all of the bolt-ons. I have been changing things up to try and figure out why my long term fuel trims are so different. I'm currently getting a lean code for bank 1. I'm running with no kittens.

List of important events.
1.Out at the track running hard on COBB Stage 2+ Tune, no kittens, no dp fix. Got a cylinder 6 misfire and then a cylinder 4 misfire not at the same time. I could turn the car off and back on and the misfire would go away until I got back on it hard again. To fix this more permanently I took the ECU map back to stock and finished out 2 more track sessions. This fixed the cylinder misfire but now I was getting the lean bank 1 code.

2. Today I was looking at the voltage numbers on the emissions. Video:

Only need to watch the first minute to get the idea. After kitten lambda voltage was going crazy. No kittens, no dp fix.

3.Then i installed the DP fix that in my understanding mimics what the kitten reading should be. This is when I made the data zap log. I find it interesting the the post kitten lambda values still change a lot but nothing like they did before. I believe pre-kitten controls the fuel but I did this just to try and take out another variable.

The gap between the long term fuel trims exists with or without the dp fix and with or without the tune.

How can I fix this problem?
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      03-21-2017, 07:19 AM   #2
iminhell1's Avatar

Drives: 2010 SG 135i auto
Join Date: May 2015
Location: Darwin, MN

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Exhaust leak?
bank 1 looks fairly consistent while 2 is pretty wild.

I'm not sure if this is common but, when i did my carbon cleaning i noticed that the rear 3 where cleaner than the front 3. to me that says he rear are getting better flow through the pcv, which also lowers octane. if yours is similar then that may explain the misfire and the misfire may explain the ltft readings?

Also I was just recently getting random misfires. My plugs are getting on in age and have about 25k on them. When I went to pull them from a hot engine all where just a smidge over hand tight. They where perfect for 24k and just recently developed misfires.
I checked my gaps and put them back in making sure to give them a little extra tightening. Then i got it good and hot and rechecked them. Everything is back to normal now.
Never hurts to recheck our plugs. I've never had a plug loosen on anything i've had in the past.
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