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      12-03-2012, 02:19 PM   #1
AndyR83
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Drives: E92 335i FBO
Join Date: Oct 2011
Location: PA

Posts: 1,007
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Help me diagnose these symptoms

Hey guys,

My car is acting a bit funny under specific, reproducible circumstances. I have a couple of theories, but I'd be interested in hearing what others think may be the cause.

I don't flog my car on a regular basis, but sometimes on a lonely, deserted road at 3am, I do like to see what it can do. I have observed on several occasions that pushing the car very hard results in a check engine light.

Situation 1: Pushing the car very hard on the highway has about a 50% chance of causing a yellow half engine light. This also includes "limp mode." Restarting the car clears the error immediately, and normal performance is restored.

Situation #2: "Launching" the car in DS mode and performing manual shifts (always around 6k, not deep in the red or anything) has about a 50% chance of causing the yellow "service engine soon" message to blink on and off for a few minutes. This does not trigger limp mode, and the light goes away after blinking for a little while.

I theorize that one of three things are the culprit.

1: The oil filter is crappy and restricting oil flow, potentially leading to an oil starvation situation. I was once told by the dealership that the oil filter they found when they did my oil after having had an indie shop do it the previous time was very poor quality, and had disintegrated causing poor oil distribution. I'm about due for an oil change, and I had an indie shop do it last time. It could be another low quality filter that is falling apart in there again, and preventing adequate oil flow.

2: The spark plugs haven't ever been changed, and I'm at about 53k miles. I thought this may be a misfiring issue. I intend to swap out the old plugs for new ones next weekend.

3: The valves may be in need of cleaning. I am looking into getting walnut blasting done, but was curious if this might be contributing to the issues.


Important background data:
The car is a 2008 335i base model

It has a JB4 tune running Map 5, though I also identified these symptoms when it ran Map 2 previously.

It has a BMS speed delimiter, but the crank position sensor is not hooked up (I folded it back on itself and covered thoe specific wires with electrical tape at time of install)

Other mods include catless DP's, FMIC,

Thanks in advance for any insight you may have.
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