BMW Rough Run, Strange Fuel Trims

David Technician Ontario Posted   Latest  
Resolved
Driveability
2009 BMW 323i 2.5L (N52N) 6-spd (A6HP19Z) — WBAPG73569A401308
Runs Rough
Fuel Trims

First time poster, looking for some insight on this N52 2.5. Quick history: replaced 6 ignition coils about 8 months ago for ignition misfires and more recently replaced the valve cove for full vacuum in crankcase. Currently the car runs, occasionally sets cylinder 4 or 6 misfire codes. During testing, it turned into a no-crank, for which the ground between the body and subframe was replaced. I've been through the secondary ignition and fuel injection and all checks out OK. It runs rough at idle, but not misfire rough. More like imbalance, but is smooth is off idle and driving with normal loads. Monitoring data, smooth running values are all +/- 1. The part that is likely causing my issues is the fuel trims are opposite bank 1 vs 2. One side goes +25, the other -25. Has anyone ever encountered this and can offer some insight? 

Not certain if related, but there is now a hard ambient temp sensor code (reading at 11*C) setting and is illuminating the SES. Found a TSB for a hard reset of cluster software with no resolution.

I'm writing this from home so forgive me for specific code info missing.

Thanks for any and all help.

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Interesting
Jason Technician
New York
Jason
 

My 435i did something very similar when the intermediate lever spring popped off the back of the lever. I had a noticeable pop from the exhaust (modified) and like you said, it didn't feel like deal hole, but it certainly wasn't BMW smooth at idle. After exhausting fuel and air, I pulled the valve cover. I was about to put it back on when I noticed a little nick on the #6 intake cam lobe. The…

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Obie Technician
Washington
Obie
 

Trim weirdness on those can be due to 02 wiring being crossed front/rear. Quick test is to disconnect B1 sensor and watch code that sets.

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Agree
John Owner
Mississippi
John
 

Are the upstream 0 2 sensors wires crossed it’s very easy to do the plugs are the same and right next each other

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Agree
Sean Technician
California
Sean
 

Plugged cat?

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John Owner
Mississippi
John
 

Definitely would do back pressure test we had misfire on 45 and 6 last week in one was back converter starting to melt and clog up

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George Technician
Alabama
George
 

Are there any odb codes?

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Glenn Owner/Technician
Texas
Glenn
 

Hi David, Being that there is an imbalance between the split exhaust, that leads me to believe there is a convertor issue on the rear 4,5, and 6 manifold convertor. A convertor melt down is possible, but what caused it? Any history of oil usage? The other idea that comes to mind is perform an injector balance test to determine integrity of injectors. Dirty or sticky injector could affect…

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Rick Technician
New York
Rick
 

something I see quite often on Bmw’s is that the O2 sensors come loose. Not always loose enough to cause an exhaust noise or rattle, but give them a check, they will draw in air and mess with your trims as well as your head.

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James Owner/Technician
Oregon
James
 

Did you replace the valve cover or just the valve cover gasket? BMW OEM parts or aftermarket? OEM coils or attermarket? Double check the gasket isn’t pinched in the right rear corner between the valve cover & head. Did you torque the valve cover bolts in the correct order & to proper spec according to SI? Did you pull the spark plugs and inspect them? Did you reset engine…

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David Technician
Ontario
David
 

OE Valve Cover, AM Coils Gasket not pinched Valve cover torqued to spec Plugs were checked and had deposits (likely oil) Adaptations reset O2 Sensors were only disconnected during valve cover replacement and trim issues were there prior Check for and found no vacuum leaks Did relearn valvetronic limits post valve cover replacement

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Mihail Technician
Maryland
Mihail
 

This could be a timing problem. What is the condition of the oil and filter, how much oil is in the engine? If not sure, flush the engine and change the oil and filter. You can also see with a scanner what the intake and exhaust cams are doing - desired vs actual position and if cam timing changes at all when rpm is increased. The vanos solenoids get plugged up and/ or fail intermittently and…

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Raymond Diagnostician
Wisconsin
Raymond
 

Had the same symptoms on a 07 328i, cylinders 4,6 miss fire codes when first start engine, verified the same condition as you did , checked all maintenance records all updates well maintained, when I first started the engine the next day I heard a rattle coming from the left side rear of engine between value cover and intake not metallic type more like plastic pieces loose then stop as engine…

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James Technician
California
James
 

Your upstream o2 sensor connectors are switched. That is what causes the fuel trim plus on one side and the minus on the other.

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Timothy Owner/Technician
Wisconsin
Timothy
 

Split/mirrored trims have two common causes: the timing has slipped at the crank, or there is an imbalance in airflow through the engine…a lugged catalyst on one bank will usually cause very lean trims on the unaffected bank, and not a lot of correction on the ‘clogged’ bank… And, of course, the reversed O2s might cause this, but, if fuel is being dispersed evenly throughout the engine, then a…

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David Technician
Ontario
David Update
 

Hi everyone. Just updating to say thanks for all the ideas. The car is set to return and I'll update further when this thing is fixed.

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David Technician
Ontario
David Resolution
 

The car never returned although the customer did. The car was sold so no further information is forthcoming. Much thanks to those who took the time to respond, hopefully this will provide some guidance to someone else.

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