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Home >> BMW >> 1987 >> 535is Standard >> Repair and Diagnosis >> Engine Performance >> System >> MOTRONIC CEC System >> Testing >> Test 1: Fuel Pressure >> No Fuel Pressure
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No Fuel Pressure

  1. Check fuel pump fuse and replace if defective. If fuse is okay, unplug electrical connector from fuel pump. Connect volt/ohmmeter between 2 wires in connector and start engine. Volt/ohmmeter should read battery voltage. If voltage is correct, replace fuel pump.
  2. If voltage reading is incorrect, check ground (Brown) wire. Connect volt/ohmmeter between wire and ground. Resistance should be zero. If not, repair wire. If resistance is correct, check power (Green/Violet) wire. Disconnect relay number one and connect volt/ohmmeter between power wire and connector No. 87 of relay socket. Resistance should be zero. If value is incorrect, repair wire.
  3. If resistance is correct, check power supply from relay No. 1. Connect volt/ohmmeter between wire No. 30 (Green/Yellow) on relay socket and ground. Turn ignition on. Meter should read battery voltage. If not, repair wire.
  4. If voltage is correct, check power supply to relay No. 1. Connect volt/ohmmeter between wire No. 86 (Red/White) of plug and ground. Start engine. Volt/ohmmeter should indicate battery voltage. If not, connect volt/ohmmeter between wire No. 87 (Red/White) of relay No. 2 and ground (relay still connected). Turn on ignition. Voltmeter should read battery voltage. If reading is incorrect, repair wire.
  5. If power supply to relay No. 1 is correct, check relay No. 1 ground. Connect volt/ohmmeter between wire No. 85 (Brown/Green) on socket and ground. Start engine. Resistance should be zero. If resistance is correct, replace relay No. 1.
  6. If voltage in last part of step 4) is correct, or if resistance is incorrect in step 5), check resistance of Brown/Green wire between connector No. 85 on relay No. 1 plug and pin No. 20 of MCU connector. Resistance should be zero. If not, repair wire. If resistance is correct, go to TEST 3: MOTRONIC CONTROL UNIT  . Correct fuel pressure should be 36-43 psi.
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