Fuel System - Long Crank Time/Low Power/Hard Start

SI B12 21 09
Engine Electrical Systems

June 2009
Technical Service

SUBJECT
Loss of Power, Extended Engine Cranking, or Engine Cranks But Does Not Start

MODEL
F01 and F02 (7 Series) with N63 engine from start of production

SITUATION
The customer complains that the engine loses power while driving; the engine will exhibit an extended cranking period before starting; or the engine will only crank and will not start. The vehicle will store various faults regarding misfire, fuel pressure, adaptations, etc. The vehicle may also store DME FC 200908 DME: internal error, monitoring fuel mass ratio lambda air mass to fuel mass, correlation error. Disregard the DME internal error fault and continue troubleshooting, using the other stored faults. Do not replace the DME.

CAUSE
Complete loss or an insufficient amount of low-pressure fuel supply, due to a separated connection at the fuel pressure regulator; or the pressure regulator is defective.

PROCEDURE
If a loss of fuel pressure is suspected, follow the procedure below for checking the low-pressure fuel system, using the ISID diagnostic tool.

1. Vehicle Test

2. Select DME

3. Call up ECU Functions

4. Diagnosis Query

5. Fuel Pressure Low

6. Measurement, activated

7. Inquiry Status

If fuel pressure bleeds down below 4000 mbar within 10 minutes of turning the engine off, or the fuel pressure does not build at all, then the pressure regulator or pressure regulator connection is suspect.

Low-pressure Fuel System Overview:
Connection to the pressure regulator (1) from the fuel
filter
Pressure regulator (2)
Low-pressure fuel pump inside the fuel tank (3)
Procedure:





Check the connection (1) from the fuel filter to the
pressure regulator (2).
If the connection is broken or disconnected, the
pressure regulator (2) is damaged and will need to be
replaced. Refer to Repair Instruction RA 16 14 220,
Removing and installing/replacing pressure regulator.





Pressure Regulator, Filter Overview (removed from
Fuel Tank):
Connection to the low-pressure fuel pump (1)
Pressure regulator (2)
Fuel filter (3)





PARTS INFORMATION

WARRANTY INFORMATION





Covered under the terms of the BMW New Vehicle Limited Warranty or the Certified Pre-Owned Program.





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