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Home >> Isuzu >> 1997 >> Trooper LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Testing >> Trouble Shooting >> Fuel System Electrical Test
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Fuel System Electrical Test

WARNING: Relieve fuel pressure before connecting fuel pressure gauge. See FUEL SYSTEM PRESSURE RELEASE  under FUEL SYSTEM.
  1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  . After performing OBD system check, go to next step.
  2. Install fuel pressure tester to fuel inlet line test fitting. Using scan tool, command fuel pump ON. Fuel pressure should build up immediately. If fuel pressure built up immediately, go to next step. If fuel pressure did not build up, go to step 4).
  3. Verify fuel pump is not running by removing gas cap and listening for fuel pump motor. Using scan tool, command fuel pump ON. If fuel pump runs for 2 seconds and turns off, fuel electrical system is operating properly. Test is complete. If fuel pump does not run or runs continuously, go to step 12).
  4. Turn ignition off. Remove fuel pump relay from fuse/relay box located in engine compartment. Using a test light connected to ground, probe battery feed circuit at fuel pump relay harness terminal No. 4 (Red/White wire). If test light illuminates, go to step 6). If test light does not illuminate, go to next step.
  5. Repair open or short in Red/White wire between fuel pump relay and fuse/relay box in engine compartment.
  6. Connect a test light between fuel pump relay harness terminals No. 1 (Red/White wire) and No. 3 (Black wire). Turn ignition on. If test light illuminates for 2 seconds then turns off, go to step 12). If test light does not illuminate, go to next step.
  7. Using test light connected to negative battery terminal, probe fuel pump relay harness terminal No. 1 (Red/White wire). Turn ignition on. If test light illuminates for 2 seconds then turns off, go to next step. If test light does not illuminate, go to step 9).
  8. Repair open in Black wire between fuel pump relay and ground.
  9. Check for open or short in Red/White wire between fuel pump relay and PCM connector C-3 terminal E13. Repair as necessary. If circuits are okay, go to step 10).
  10. Check for poor connections at fuel pump relay. Repair as necessary. If connections are okay, go to step 11).
  11. Replace PCM. Verify system is operating properly.
  12. If removed, reinstall fuel pump relay. Disconnect fuel pump electrical connector at fuel tank. Using a test light connected to ground, probe fuel pump harness terminal No. 1 (Black/Red wire). Using scan tool, command fuel pump ON. If test light illuminates for 2 seconds, go to step 15). If test light does not illuminate for 2 seconds, go to next step.
  13. Honk horn to verify horn relay is functional. Substitute horn relay for fuel pump relay. Repeat test procedure from step 12). If test light does not illuminate for 2 seconds, go to next step. If test light illuminates for 2 seconds, go to step 17).
  14. Check for open or short in Red or Black/Red wire between fuel pump relay and fuel pump. Check for blown FUEL PUMP fuse F-10 (15-amp) located in fuse/relay box in engine compartment. Repair or replace as necessary. Reinstall horn relay.
  15. Connect a test light between fuel pump harness terminals No. 1 (Black/Red wire) and No. 2 (Black wire). Using scan tool, command fuel pump ON. If test light illuminates for 2 seconds, go to step 18). If test light does not illuminate for 2 seconds, go to next step.
  16. Repair open in Black wire between fuel pump and ground.
  17. Replace fuel pump relay. Reinstall horn relay.
  18. Replace fuel pump.
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