Vehicle Initial Inspection

Vehicle initial inspection

The cause of a driveability complaint or Diagnostic Trouble Code (DTC) can often be found and repaired quickly by performing a thorough initial inspection. The initial inspection should include the following:

- Check the battery state of charge; perform a battery load test to ensure that battery performance is satisfactory.

NOTE: If the CHECK ENGINE MIL is illuminated, DTCs must be retrieved prior to disconnecting the vehicle battery.

- Check the battery connections; clean and remake as necessary.
- Visually check for disconnected wires to the engine management input and output components.
- Visually check the engine management system for chaffed wire insulation or bare wires.
- Check for loose or corroded ground connections at the bulkhead stud and at the intake manifold stud.
- Check for loose or corroded engine ground strap connections.
- Check the ECM connector pins for corrosion. Switch off the ignition and disconnect the yellow and blue ECM connectors. Clean the connector and ECM pins. Spray the ECM pins with JLM 11472. Reconnect the connectors.

- Test the engine management system ECM power supplies and ground connections:

ECM Connectors:

1. Direct battery power is supplied to the ECM through the blue connector pin 14. Test the voltage at pin 14 by back probing the blue connector with a voltmeter. If battery voltage is present, proceed to the next step; if the voltage reading is zero, troubleshoot the circuit between the battery and the ECM. Refer to the wiring diagrams in the REFERENCE section.

ECM Power Supply:

2. Ignition switched power is supplied to the ECM through the yellow connector pin 1 and through the blue connector pins 10 and 22. Test the voltage at yellow pin 1 and blue pins 10 and 22 by switching ON the ignition and back probing the three pins with a voltmeter. Battery voltage should be present and the readings should be within 200 mV of the reading from Step 1 above. If correct voltage is present, proceed to the next step; if the voltage reading is incorrect, troubleshoot the circuit between the battery, ignition switch and the ECM. Refer to the wiring diagrams in the REFERENCE section.

ECM Ground Connection:

3. Ground connection between the ECM, the engine and the chassis varies by the vehicle model year and between the XJ6 Sedan Range and XJS Range models. Refer to the wiring diagrams in the Reference section. The ECM grounds are made at the yellow connector pin 18 and at the blue connector pins 11, 23 and 24. Disconnect the battery and test the ground connections at yellow pin 18 and blue pins 11, 23 and 24 by back probing the four pins with an ohm meter. If the reading is zero ohms, ground connection is complete; if resistance is indicated, troubleshoot the ground circuit.

Additional checks for drivability complaints or DTCs related to fuel metering should include the following:

- Check The Air Filter Condition.

- Check The Fuel Pressure:
1. Depressurize the fuel delivery system by running the engine and removing the fuel pump relay. When the engine stops, switch OFF the ignition and reinstall the relay. During this step, DTC 22 will flag.

Fuel Pressure:

2. "Tee" the fuel pressure gauge into the system at the inlet hose to the fuel rail. Restart the engine and observe the fuel pressure with the manifold vacuum hose connected to and disconnected from the fuel pressure regulator.
Normal fuel pressure:
34-38 psi at idle (vacuum connected to fuel pressure regulator)
42-45 psi (vacuum disconnected from fuel pressure regulator)

3. Switch OFF the ignition and observe the gauge for a drop in fuel pressure. Maximum pressure drop - 10 psi in the first minute.
If the pressure drop exceeds 10 psi in the first minute, suspect the following:
Fuel pressure regulator
External fuel pump check valve (1990 MY)
Fuel tank internal pump hoses and connections (1991 MY ON)
Injector leakage

4. Clear DTC 22. Refer to General Diagnostic Procedure. General Diagnostic Procedure

- Check For Water In The Fuel

- Check The Ignition Oscilloscope Pattern. A fault in the ignition system secondary circuit will usually cause an engine misfire. Use above examples of ignition secondary voltage oscilloscope patterns as a guide to diagnosing the problem.

Secondary Voltage Oscilloscope Patterns:

- Correct, repair and/or replace defective components as necessary, then road test the vehicle to check for a reoccurring problem.