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Home >> BMW >> 1982 >> 733i Automatic Trans >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> BMW MOTRONIC Emission Control System >> Testing >> Test 1: Fuel Pressure >> No Fuel Pressure
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No Fuel Pressure

  1. Check fuel pump fuse and replace if broken. If fuse is okay, pull off electrical connector on fuel pump. Connect voltmeter between the 2 wires in connector and start engine. Voltmeter should read battery voltage. If voltage is correct, replace pump.
  2. If voltage reading is incorrect, check ground (Brown) wire: Connect ohmmeter between wire and ground. Resistance should be zero. If not, repair wire. If resistance is correct, check power (Green/Violet) wire: Disconnect Relay 1 and connect ohmmeter between power wire and connector 87 of relay socket. Resistance should be zero. If value is incorrect, repair wire.
  3. If resistance is correct, check power supply from Relay 1: Connect voltmeter between wire 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 1: Connect voltmeter between wire 86 (Red/White) of plug and ground. Start engine. Voltmeter should show battery voltage. If not, connect a voltmeter between wire 87 (Red/White) of Relay 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 1 is correct, check Relay 1 ground: Connect ohmmeter between wire 85 (Brown/Green) on socket and ground. Start engine. Resistance should be about zero. If resistance is correct, replace Relay 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 85 on Relay 1 plug and pin 20 of MCU connector. Resistance should be about zero. If not, repair wire. If resistance is correct, go to TEST 3  for Motronic Control Unit.
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