Test Description
Test Number 1) A "Service Engine Soon" light "ON" is a basic test to determine if there is a 12 volt supply and ignition 12 volts to ECM. No ALDL may be due to an ECM problem and CHART A-2 will diagnose ECM. If TPS is over 2.5 volts the engine may be in the clear flood mode which will cause starting problems. If coolant sensor is below -30°C, the ECM will provide fuel for this extremely cold temperature which will severely flood the engine.
Test Number 2) Voltage at spark plug is checked using spark tester tool ST-125 (J 26792) or equivalent. No spark indicates a basic ignition problem.
Test Number 3) While cranking engine there should be no fuel spray with injector disconnected. Replace an injector if it sprays fuel or drips like a leaking water faucet.
Test Number 4) Use an injector test light like J 34730, BT-8329A or equivalent, to test injector circuit. A blinking light indicates the ECM is controlling the injector.
Test Number 5) This test will determine if there is fuel pressure at the injector and that the injector is operating.
Test Number 1) A "Service Engine Soon" light "ON" is a basic test to determine if there is a 12 volt supply and ignition 12 volts to ECM. No ALDL may be due to an ECM problem and CHART A-2 will diagnose ECM. If TPS is over 2.5 volts the engine may be in the clear flood mode which will cause starting problems. If coolant sensor is below -30°C, the ECM will provide fuel for this extremely cold temperature which will severely flood the engine.
Test Number 2) Voltage at spark plug is checked using spark tester tool ST-125 (J 26792) or equivalent. No spark indicates a basic ignition problem.
Test Number 3) While cranking engine there should be no fuel spray with injector disconnected. Replace an injector if it sprays fuel or drips like a leaking water faucet.
Test Number 4) Use an injector test light like BT-8320 or equivalent, to test injector circuit. A blinking light indicates the ECM is controlling the injector.
Test Number 5) This test will determine if there is fuel pressure at the injector and that the injector is operating.
Test Number 1) This test will determine if ignition module is generating a reference pulse, if wiring is at fault or if ECM is at fault. By touching and removing a test light, connected to 12 volts, to circuit 430, a reference pulse should be generated. If injector test light blinks, ECM and wiring are OK.
Test Number 2) This step tests for 12 volts to injector. It will also determine if there is a short to voltage on ECM side of circuit.
Test Number 3) This test checks for continuity to ECM.
Scheme 1
Scheme 2
Test Number 1) This test will determine if ignition module is generating a reference pulse, if wiring is at fault or if ECM is at fault. By touching and removing a test light, connected to 12 volts, to circuit 430, a reference pulse should be generated. If injector test light blinks, ECM and wiring are OK.
Test Number 2) This step tests for 12 volts to injector. It will also determine if there is a short to voltage on ECM side of circuit.
Test Number 3) This test checks for continuity to ECM.
Scheme 3
Scheme 4
Test Number 1) Turns "ON" the fuel pump if circuit 120 wiring is OK. If the pump runs, it may be a fuel pump relay circuit problem, which the following steps will locate.
Test Number 2) The next two steps check for power and ground circuits to the relay.
Test Number 3) Determines if ECM can control the relay.
Test Number 4) The oil pressure switch serves as a backup for the fuel pump relay to help prevent a "no start" situation. If the fuel pump relay was found to be inoperative, the oil pressure switch circuit should also be tested to determine why it did not operate the fuel pump.
Scheme 5
Scheme 6
Test Number 1) This procedure applies direct voltage to run the fuel pump. If the pump runs, it may be a fuel pump relay circuit problem which the following steps will locate.
Test Number 2) This step checks voltage from the battery and the ground circuit to the relay.
Test Number 3) This test determines if there is voltage from the ECM, terminal "A1", to terminal "D" on the relay connector.
Test Number 4) This completes the fuel pump relay circuit but if this diagnosis was used because the engine would not run then oil pressure switch should also be diagnosed.
Test Number 1) Pressure, but less than 9 psi falls into two areas
- Regulated pressure but less than 9 psi - Amount of fuel to injector OK but pressure is too low. System will be lean running and may set Code 44. Also, hard starting cold and poor overall performance.
- Restricted flow causing pressure drop - Normally, a vehicle with a fuel pressure of less than 9 psi at idle will not be driveable. However, if the pressure drop occurs only while driving, the engine could surge and stop when pressure is too low.
Test Number 2) Restricting the outlet side of the gage allows the pump to develop its maximum pressure (dead head pressure). With battery voltage applied to the pump test terminal, fuel pressure should rise to 13-15 psi as the pressure gage outlet hose is gradually pinched.
Test Number 3) This test determines if high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.