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Rough Engine Running at Cold Start

ASKED BY:

Francis Dance

FSC MEMBER:

Yes

CATEGORY:

Engine

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Question

Hi Gil, My 1997 BMW 528i with M52 engine and THM-R1 trans (A45 270R, 4 speed) recently began exhibiting a strange cold start behavior after the overnight. It seems to be running on only a few cylinders for perhaps 30 seconds max, then smooths out and runs fine. Plugs were replaced a year ago, 5k miles. The car now has 75k miles on it. To me, it feels like a fuel injector pressure loss, like a check valve not holding pressure. It will only do it when the engine is totally cold; all subsequent starts on the day usually are fine. Any ideas?

Answer

Hello Mr. Dance, I don’t think it is a fuel pressure loss, the symptom for that issue is a longer crank time when cold. That issue most commonly happens with an air leak in the engine. I would check for air leaks but keep in mind that it may be a very small leak. The other likely issue is the air mass meter. To help you further I would have to know what the fuel trim numbers are, the ony way to get that is a scan tool, any tool will do, you just have to look at the live data section of it. Please let me know if I can help you further. Thank you.

Gil Neves

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This Post Has One Comment

  1. Thanks, Gil, for your recommendation to determine what the fuel trim numbers are with a scan tool. I will then see what the live data section of it shows and advise.

    Best regards,

    Fran Dance

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