Fuel Pressure: Notes
Basic diagnosis of fuel system should begin with determining fuel system pressure.
WARNING:
Residual fuel pressure may exist in fuel lines and component parts. Use care when removing fuel lines to release fuel pressure and prevent personal injury. Do not allow fuel to flow onto engine or electrical parts or allow an open flame in area while testing fuel system components.
- Install fuel pressure gauge on the front (inlet) side of pressure regulator. Plug outlet line from pressure regulator. Remove fuel pump relay.
- On 3 series vehicles, fuel pump relay is on bracket on left front shock tower (center relay on bracket). On 5 and 7 series vehicles, fuel pump relay is in relay box in right rear corner of engine compartment. On 635CSi vehicles, fuel pump relay is on left side of engine compartment, attached to outside of relay/fuse box.
- On all models, note terminal identification stamped on bottom of fuel pump relay. Install jumper wire between terminls No. 30 and 87 of relay connector. This will turn on the fuel pump. If fuel pump fails to operate, check fuel pump fuse.
- Note if fuel pressure exists. This is the full pressure available from fuel pump. To check fuel pressure regulator, remove plug from return line. Install jumper wire between terminals No. 30 and 87 of fuel pump relay and note pressure.
- If pressure drops rapidly, remove jumper wire and plug return line. Reinstall jumper wire. If pressure now remains constant, replace pressure regulator. If pressure still drops, check for leak in front of the pressure regulator.
FUEL PUMP PERFORMANCE
| Application | psi (kg/cm2 ) | ||||
|---|---|---|---|---|---|
| 525i | (1) | ||||
| All Others | (2) 40-46 (2.8-3.2) | ||||
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