Fuel - System Rattle, Hum, Buzz, Knocks When Cold

GROUP 13
Fuel Systems

Bulletin Number
13 01 97

Woodcliff Lake, NJ
June 1997
Product Engineering

SUBJECT:
Fuel System Noises

MODEL:
525i E34 with M50 Engine

Situation:
A noise in the fuel system, primarily at ambient temperatures below 40 degrees F, may be heard which is described as a rattle, hum, buzz, or knock, and usually disappears as the engine reaches operating temperature.

Field reports have indicated that in some cases the noise travels from the engine compartment toward the rear of the vehicle via the fuel lines.

Cause:
The noise is due to fuel system pulsations generated by the fuel pump and injectors which are further stimulated by the fuel pressure regulator manufactured by Pierburg.

Correction:
In case of a customer complaint if a noise is heard as described above, the Pierburg fuel pressure regulator should be replaced with a Bosch regulator.

Troubleshooting note:
With the noise present, move/reposition the fuel supply and return lines to verify if the noise level or pitch changes. If it does this indicates the noise is coming from the fuel system and the Pierburg regulator should be replaced with the Bosch type.





Parts Information;
Only Bosch fuel pressure regulators are available as replacement parts and may be ordered under the following part number:





Warranty Information:
Covered under the terms of the BMW Emissions Warranty.