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Old 08-04-2012, 05:02 AM
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Fudman Fudman is offline
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Location: Sudbury, MA
 
Join Date: Apr 2007
Posts: 6,132
Mein Auto: '02 530i Sport auto
To assist in your diagnosis, I suggest you read these linked articles.

http://www.autohausaz.com/html/fuelpumps.html
http://www.aa1car.com/library/2003/us60324.htm

Ensure that you have spark and air, first (which you probably do since you can easily start the car when warm). Given that your car starts easily soon after previous use but has problems after sitting awhile, I believe that your fuel injection system is having trouble maintaining residual fuel pressure, long after shutdown. The Bosch fuel injection system requires 40 psi or more. Loss of pressure will create hard starting problems. Since the M54 has the integrated pressure regulator on the fuel filter, I would look there first as the cause (it is also easier and cheaper to replace than a fuel pump and is considered normal maintenance).

As a test, at your next cold start, try letting the fuel pump pressurize the fuel injection system first. Turn the key until you can hear the fuel pump start up. Leave it in this condition for a minute or so. Then attempt to start it. If it fires up, the check valve within the fuel filter is probably failing and causing residual fuel pressure to bleed off. Replacing the fuel filter should alleviate this issue.

Please report back on the resolution to your problem as this can be very helpful to others with similar issues.
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