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Home >> Mercedes Benz >> 1990 >> 300CE >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Testing >> Fuel Pump Performance >> Fuel Pump Relay
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Fuel Pump Relay

  1. Remove fuel pump relay from relay board. Connect positive lead of voltmeter to socket No. 8 (terminal No. 30) and negative lead to socket No. 11 (terminal No. 31) of connector. Measure voltage. If reading is 12 volts, go to step 3). If voltage is zero, go to next step.
  2. Remove negative lead of voltmeter from socket No. 11 (terminal No. 31) and connect to vehicle ground. If reading is 12 volts, check Brown wire from terminal No. 31 for short or open. If voltage is zero, check Red wire from terminal No. 30 for short or open. Repair wiring if necessary.
  3. Turn ignition on and check voltage at socket No. 9 (terminal No. 15) of connector. If reading is zero volts, check Black/Red wire from terminal No. 15 to fuse box for open or short. Repair wiring if necessary. If reading is 12 volts, go to next step.
  4. Using dwell meter, connect positive lead to socket No. 10 (terminal TD). Dwell angle should be 7-34 degrees. If dwell reading is incorrect, inspect Green/Yellow wire from jack 10 (terminal TD) to EZL (transistor ignition) switching unit for open or short. If wiring is acceptable, replace switching unit. If dwell reading is within specifications go to next step.
  5. Bridge socket No. 7 (terminal No. 87) and socket No. 8 (terminal No. 30) with jumper wire. If fuel pump is running, test is completed. If fuel pump is not running, go to next step.
  6. Verify Black/Red/White wire from terminal No. 87 to fuel pump is not shorted. If no open or short is found, replace fuel pump relay. If fuel pump still does not run, replace fuel pump.
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