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#1
03-07-2007, 10:59 PM
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Fuel Trim Malfunction
Check Engine light, ran an OBD-II Scan and it came back Fuel Trim Malfunction (Bank 1 and Bank 2). Anyone know how to corner this problem and eliminate it?
Mike
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1998 BMW 740i 01/1998 
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#2
03-08-2007, 12:19 AM
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Re: Fuel Trim Malfunction
I'm guessing your mixture is too lean and it's possibly running a bit rough and there isn't enough fuel getting to the engine. A rich mixture is too much fuel, but that error is usually related to O2 sensors. It might be the O2, but 'trim malfunction,' you're looking at a vacuum leak. Check the oil seperator valve then the throttle body gasket and then the intakes. Most likely a vacuum leak and the throttle body, oil seperator and intake are the most likely. Run your hand around the bottom of the throttle body and oil seperator, if it's greasy/oily there, there's a leak.
If there is no leak, test the MAF sensors...they might need cleaning, and in a worst case senario, might need replacing.
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1990 E32 750iL --> Pictures Production: 02/1990 Johan and Sean's E32 Page - Repairs and How-to's E38.org - Information and tech tips for BMW's Shogun's E32 Tech-Tips Gale's Repair Page ETK Online
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#3
03-26-2007, 09:16 PM
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Re: Fuel Trim Malfunction
In my case it is not a vacuum leak. I currently have the Fuel Trim Malfunction codes for both banks and it is in the shop now. The mechanic verified it is not a vacuum leak. His suspicion is that it is a bad Air Mass Meter because the voltage readings are not what they should be, during an instrumented test drive. He did not have a new Air Mass meter to verify today. I will know tomorrow if this is correct.
The Air Mass Meter was replaced and it runs great, much more power. No more Fuel Trim Malfunction codes. Last edited by ryunk; 03-28-2007 at 05:53 PM.
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