Fuel trims

MikeHawk7 · 10-20-2020, 02:10 AM

I'm chasing a negative fuel trim issue on both banks (running rich); stock DME tuning (241E).

About -17% at idle, about -3% while driving, never really going positive. These are the long-term trims, short-term isn't significant. Seems a bit excessive. The numbers are similar on both banks.

Bad MAP sensor or O2 sensors? Leaky injectors? Overzealous pressure regulator?

Plugs changed 8k ago, already changed fuel pressure sensor, fuel tank breather valve, and donut gaskets after the header.

Is this normal? What else should I check?

Kwike92M3 · 10-22-2020, 06:52 AM

I would start with looking at items that affect BOTH banks, IE MAP sensor, low pressure fuel regulator, etc.
However, short term fuel trims DO give valuable information on what to expect of long term fuel trims, so that info could be helpful.
I wouldnt say O2 sensors simply because different upstream O2s control either side of the engine.
Are you getting a check engine light with P0172/P0175, or are you just tinkering with data?

MikeHawk7 · 10-25-2020, 01:32 AM

Quote:

Originally Posted by Kwike92M3

I would start with looking at items that affect BOTH banks, IE MAP sensor, low pressure fuel regulator, etc.
However, short term fuel trims DO give valuable information on what to expect of long term fuel trims, so that info could be helpful.
I wouldnt say O2 sensors simply because different upstream O2s control either side of the engine.
Are you getting a check engine light with P0172/P0175, or are you just tinkering with data?

No CEL, just reading my PID data looking to optimize my engine, trying to get trims within +/- 5%. How do I troubleshoot the MAP sensor? I have a variety of OBD scanners and software/apps including a OBDLink MX+, BimmerLink, Foxwell NT530, K-DCAN/laptop, ISTA, etc.

STFTs don't seem too wild, LTFTs are the issue.

I believe the pressure regulator is in-tank?

e36mikee · 08-12-2026, 11:52 PM

did you ever solve this issue? just was looking at data tonight and very negative LTFT on idle. going to do more logging and investigating when i get the chance. my injectors, purge valve, and pressure sensor are all brand new.

10-20-2020, 02:10 AM	#1
MikeHawk7 Second Lieutenant 152 Rep 206 Posts Drives: 2013 M3: E92, ZCP, DCT Join Date: Aug 2017 Location: San Diego, CA iTrader: (5) Garage List 2003 BMW 530i [0.00] 2013 BMW M3 [0.00]	Fuel trims - negative I'm chasing a negative fuel trim issue on both banks (running rich); stock DME tuning (241E). About -17% at idle, about -3% while driving, never really going positive. These are the long-term trims, short-term isn't significant. Seems a bit excessive. The numbers are similar on both banks. Bad MAP sensor or O2 sensors? Leaky injectors? Overzealous pressure regulator? Plugs changed 8k ago, already changed fuel pressure sensor, fuel tank breather valve, and donut gaskets after the header. Is this normal? What else should I check? __________________ -Mike M. 2013 M3 [E92, Alpine White, ZCP, DCT] 2003 530i
	Appreciate 0 Tweet Quote

10-22-2020, 06:52 AM	#2
Kwike92M3 Private First Class 81 Rep 146 Posts Drives: 2011 E92 M3 Supercharged Join Date: Aug 2014 Location: Dallas iTrader: (2)	I would start with looking at items that affect BOTH banks, IE MAP sensor, low pressure fuel regulator, etc. However, short term fuel trims DO give valuable information on what to expect of long term fuel trims, so that info could be helpful. I wouldnt say O2 sensors simply because different upstream O2s control either side of the engine. Are you getting a check engine light with P0172/P0175, or are you just tinkering with data?
	Appreciate 0 Quote

08-12-2026, 11:52 PM	#4
e36mikee New Member 14 Rep 14 Posts Drives: e92 m3 Join Date: Apr 2026 Location: CA iTrader: (0)	did you ever solve this issue? just was looking at data tonight and very negative LTFT on idle. going to do more logging and investigating when i get the chance. my injectors, purge valve, and pressure sensor are all brand new.
	Appreciate 0 Quote