Engine Controls - Basic Testing: Diagnosis Isuzu Trooper II

VISUAL INSPECTION

Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Check for any blown fuses. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. See VACUUM DIAGRAMS article to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.

FUEL PUMP PRESSURE TEST

Note. Begin basic fuel system diagnosis with testing fuel pressure.

1. Turn ignition off. Ensure A/C is off (if equipped). Release fuel system pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-16258-S18347914732000122900000). Attach Fuel Pressure Gauge Set (J-34730-1 ) to fuel rail or fuel supply line. (Scheme 1) Turn ignition on. Allow fuel pump to run for about 2 seconds. Check fuel pressure. See «FUEL PUMP PERFORMANCE»(ref-16258-S13934813352002013000000) table.
2. With engine at normal operating temperature, turn ignition on and let fuel pressure build to maximum pressure. Start engine and observe pressure. See «FUEL PUMP PERFORMANCE»(ref-16258-S13934813352002013000000). If pressure drop is as specified, system is operating properly. If pressure does not drop as specified, see «FUEL SYSTEM DIAGNOSIS»(ref-16258-S05241150392000122900000) procedure. Locate and repair leak or restriction in fuel system.

FUEL PUMP PERFORMANCE

Scheme 1

FUEL PUMP RELAY TEST

1. PCM supplies power to relay as long as PCM receives ignition reference signals or starter crank signal. To run fuel pump without starting engine, remove relay and jumper terminals No. 2 and 4.
2. To test relay, use jumper wires to ground terminal No. 3 of relay and apply battery voltage to terminal No. 1 of relay. Using ohmmeter, check for continuity between relay terminals No. 2 and 4. If continuity does not exist, replace relay.

TROUBLE SHOOTING

Note. To reprogram EEPROM or to program PCM after it has been replaced, special equipment from manufacturer is required.

Note. To identify component terminals and wire colors, see appropriate wiring diagram in WIRING DIAGRAMS article.

FUEL SYSTEM ELECTRICAL TEST

1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-16258-S04817147262000122900000) . 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.

FUEL SYSTEM DIAGNOSIS

1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(ref-16258-S04817147262000122900000) . After performing OBD system check, go to next step.
2. Turn ignition off. Turn A/C system off. Relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEM. Install Fuel Pressure Gauge (J-34730-1 ). Turn ignition on. Fuel pump should run for 2 seconds (it may be necessary to turn ignition on several times to obtain highest possible fuel pressure). If fuel pressure is 42-55 psi (3.0-3.9 kg/cm 2 ), go to next step. If fuel pressure is not 42-55 psi (3.0-3.9 kg/cm 2 ), go to step 17).
3. After fuel pump has shut off, fuel pressure should stabilize and remain constant. If fuel pressure remains constant, go to next step. If fuel pressure does not remain constant, go to step 12).
4. With vehicle at normal operating temperature, turn ignition on. Allow fuel pressure to build (it may be necessary to turn ignition on several times to obtain highest possible fuel pressure). Start engine. If fuel pressure drops 3-15 psi (0.2-1.0 kg/cm 2 ), go to next step. If fuel pressure does not drop 3-15 psi (0.2-1.0 kg/cm 2 ), go to step 9).
5. If fuel pressure is suspected of dropping off during acceleration, cruise or hard cornering, go to next step. If fuel pressure is okay, check for improper fuel.
6. Inspect fuel filter and fuel supply line. If no restriction is found, go to next step. If restriction is found, repair as necessary.
7. Remove fuel tank. Inspect fuel pump strainer for a restriction. Check fuel line for leaks. Verify correct fuel pump is installed. If no problem is found, go to next step. If a problem is found, repair as necessary.
8. Replace fuel pump. Verify system is operating properly.
9. Disconnect vacuum hose to fuel pressure regulator. With engine at idle, apply 12-14 in. Hg. of vacuum to fuel pressure regulator. If fuel pressure drops 3-15 psi (0.2-1.0 kg/cm 2 ), go to next step. If fuel pressure does not drop 3-15 psi (0.2-1.0 kg/cm 2 ), go to step 11).
10. Locate and repair loss of vacuum to fuel pressure regulator. See «VACUUM DIAGRAMS»(ref-16278) article. Verify system is operating properly.
11. Replace fuel pressure regulator. Verify system is operating properly.
12. Using scan tool or 10-amp fused jumper wire connected to fuel pump relay, pressurize fuel system. Using locking pliers, pinch fuel supply hose. If fuel pressure remains constant, go to next step. If fuel pressure does not remain constant, go to step 15).
13. Check fuel supply line for leaks. Repair as necessary.
14. Remove fuel tank. Check for leaks in hose or in-tank fuel line. Repair as necessary. If no leaks are found, go to step 8).
15. Remove locking pliers from fuel supply hose. Using locking pliers, pinch fuel return line. Using scan tool or 10-amp fused jumper wire connected to fuel pump relay, pressurize fuel system. Pinch fuel supply hose. If fuel pressure does not remain constant, go to next step. If fuel pressure remains constant, go to step 11).
16. Locate and replace leaking fuel injector(s). Verify system is operating properly.
17. If fuel pressure is greater than 55 psi (3.9 kg/cm 2 ), go to next step. If fuel pressure is not greater than 55 psi (3.9 kg/cm 2 ), go to step 21).
18. Relieve fuel system pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-16258-S18347914732000122900000) under FUEL SYSTEM. Disconnect fuel return line from fuel rail. Connect a flexible hose to fuel rail return outlet passage, and place open end of hose into approved gasoline container. Turn ignition off for about 10 seconds. Turn ignition on. While fuel pump is running, observe fuel gauge. If fuel pressure is 42-55 psi (3.0-3.9 kg/cm 2 ), go to next step. If fuel pressure is not 42-55 psi (3.0-3.9 kg/cm 2 ), go to step 20).
19. Repair restriction in fuel return line. Verify system is operating properly.
20. Check for restriction in fuel rail outlet passages. Repair as necessary. If there is no restriction, go to step 11).
21. If fuel pressure is greater than 0 psi (0 kg/cm 2 ), go to next step. If fuel pressure is not greater than 0 psi (0 kg/cm 2 ), go to step 23). CAUTION: In the next step, DO NOT allow fuel pressure to exceed 60 psi (4.2 kg/cm 2 ), or fuel pressure regulator or fuel pressure gauge may be damaged.
22. Using scan tool or 10-amp fused jumper wire connected to fuel pump relay, pressurize fuel system. Using pliers, gradually pinch fuel return hose. If fuel pressure is greater than 55 psi (3.9 kg/cm 2 ), go to step 11). If fuel pressure is not greater than 55 psi (3.9 kg/cm 2 ), go to step 7).
23. Using scan tool or 10-amp fused jumper wire connected to fuel pump relay, command fuel pump ON. Remove gas cap, and listen for sound of fuel pump. If fuel pump is running, go to step 7). If fuel pump is not running, go to «FUEL SYSTEM ELECTRICAL TEST»(ref-16258-S33701140552000122900000) .