Extremely high fuel trims under low load, need opinions.

d4700 · 11-01-2023, 06:25 PM

Currently seeing around 20% long term fuel trims under idle, cruise, light acceleration (vacuum). Long term trims seem to zero out under boost, and AFRs look alright.

I've done a low pressure manifold smoke test to check for leaks, can't find anything. No odd noises, leaks, anything like that. Verified proper operation of the PCV system. No misfires, car runs alright and boosts well, but starts are a bit stumbly and low RPM performance is a little bit weaker than I've come to expect with this engine. No codes.

Replaced MAP sensor to no avail. O2 sensor data looks good and both banks are consistent with each other. Index 12 injectors, although I do not know the age of them. Spark plugs and coils are new. I changed the valve cover a couple months ago, but I used an Amazon aftermarket one. Not sure if this could be the source of my issues.

What I wanted to ask is this... As read by the MAP sensor (not the one in the charge pipe), my intake manifold vacuum is at -7.7 psi or -15.67 inHg, which based on some research seems to be below normal. I am at 1000 ft MSL, so at sea level it would probably be more around -16.67 inHg. Can anyone chime in with normal vacuum values for this engine, and whether or not I should continue to chase an air leak? I would appreciate any input or opinions. Cheers.

Sgop335 · 11-01-2023, 07:19 PM

-8.5 psi at idle is ok on gear, at neutral mine is more like -9.1.

How are the stfts at idle when ltfts are high?

d4700 · 11-01-2023, 07:27 PM

Quote:

Originally Posted by Sgop335

-8.5 psi at idle is ok on gear, at neutral mine is more like -9.1.

How are the stfts at idle when ltfts are high?

Unfortunately my -7.7psi reading is in neutral. I'm not quite sure what it is in gear, but I can check.

I'm thinking maybe leaking intake manifold gaskets or cracked valve cover? I looked all over for cracks and leaks and couldn't find any, but I suppose there's some things you can't see at first glance.

For some reason I'm not able to log STFTs in Protool, so it's been a while since I checked. But last I looked in INPA, they were within ±4%. The long term trims seem consistent and don't change much.

11-01-2023, 06:25 PM	#1
d4700 Registered 0 Rep 2 Posts Drives: 2009 BMW 535i xDrive Touring Join Date: Mar 2023 Location: Phoenix, Arizona iTrader: (0)	Extremely high fuel trims under low load, need opinions. Currently seeing around 20% long term fuel trims under idle, cruise, light acceleration (vacuum). Long term trims seem to zero out under boost, and AFRs look alright. I've done a low pressure manifold smoke test to check for leaks, can't find anything. No odd noises, leaks, anything like that. Verified proper operation of the PCV system. No misfires, car runs alright and boosts well, but starts are a bit stumbly and low RPM performance is a little bit weaker than I've come to expect with this engine. No codes. Replaced MAP sensor to no avail. O2 sensor data looks good and both banks are consistent with each other. Index 12 injectors, although I do not know the age of them. Spark plugs and coils are new. I changed the valve cover a couple months ago, but I used an Amazon aftermarket one. Not sure if this could be the source of my issues. What I wanted to ask is this... As read by the MAP sensor (not the one in the charge pipe), my intake manifold vacuum is at -7.7 psi or -15.67 inHg, which based on some research seems to be below normal. I am at 1000 ft MSL, so at sea level it would probably be more around -16.67 inHg. Can anyone chime in with normal vacuum values for this engine, and whether or not I should continue to chase an air leak? I would appreciate any input or opinions. Cheers.
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11-01-2023, 07:19 PM	#2
Sgop335 Colonel 650 Rep 2,020 Posts Drives: 07 335i e92, 08 535i Join Date: Jun 2014 Location: MD iTrader: (1)	-8.5 psi at idle is ok on gear, at neutral mine is more like -9.1. How are the stfts at idle when ltfts are high? __________________ 335i e92 TPC 19Ts
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