1990 BMW 535iFACTORY OEM SERVICE PROCEDURE

Fuel Pressure: Notes

Basic fuel system diagnosis should begin with fuel system pressure test.

WARNING: Residual fuel pressure may exist in fuel lines and component parts. Release fuel pressure and use care when removing fuel lines to 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.
  1. Install fuel pressure gauge on the front (inlet) side of pressure regulator. Plug outlet line from pressure regulator. Remove fuel pump relay.
  2. On 325 series vehicles, fuel pump relay is on bracket on left front shock tower (center relay on bracket). On 525i, 535i and 735i series vehicles, fuel pump relay is in relay box in right rear corner of engine compartment.
  3. On all models, note terminal identification number stamped on bottom of fuel pump relay. Install jumper wire between terminals No. 30 and 87 of relay connector. This will turn on the fuel pump. If fuel pump fails to operate, check fuel pump fuse.
  4. Note if fuel pressure exists. This is the full pressure available from fuel pump. To check fuel pressure regulator, remove plug from outlet line. Install jumper wire between terminals No. 30 and 87 of fuel pump relay and note pressure.
  5. 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. Remove fuel pressure gauge.
FUEL PUMP PERFORMANCE

Application psi (kg/cm2 )
525i (1)
All Other Models (2) 40-46 (2.8-3.2)
(1) Information not available from manufacturer.
(2) Pressure checked with vacuum hose disconnected from pressure regulator. No other pressure specifications given from manufacturer.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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