Main Relay (Computer/Fuel System): Testing and Inspection

Multiport Fuel Injection Relay:

Engine Control Module Connector--For Pin Applications See Components:

Failure of the Multiport Fuel Injection Control (MFI) relay could interrupt power supply to the fuel pump, injectors and ECM, resulting in start failure.

CAUTION: Use caution when connecting jumper wires to the relay. If the polarity is incorrectly connected, the relay will be damaged.

Fig. 1 Relay Test:

COMPONENT TEST
1. Supply 12 VDC to relay terminals 8 (-) and 10 (+). Using a voltmeter, check for voltage between terminals 4 (+) and 8 (-) and between terminals 5 (+) and 8 (-). Refer to Fig. 1.

Voltage
12 VDC

Fig. 2 Relay Test:

2. Supply 12 VDC to relay terminals 6 (-) and 9 (+). Using an ohmmeter, check for continuity between terminals 2 and 3. Refer to Fig. 2.

Continuity
Should exist when voltage is supplied.
Should NOT exist when voltage is NOT supplied.

Fig. 3 Relay Test:

3. Supply 12 VDC to relay terminals 7 (-) and 3 (+). Using a voltmeter, check for voltage between terminals 2 (+) and supply battery ground terminal. Refer to Fig. 3.

Voltage
12 VDC when terminal 7 is connected.
0 VDC when terminal 7 is NOT connected.

HARNESS TEST
1. Disconnect the negative battery cable and the ECM connector.
2. Reconnect the negative battery cable and turn the key to the ON position.
3. Using a volt meter, check the voltage between ECM harness terminal 62 and ground.

Voltage
System voltage.

4. Turn the key to the OFF position.
5. Disconnect the MFI connector.
6. Using an volt meter, check the voltage between relay harness terminal 10 and ground.

Voltage
System voltage.

7. Using a ohm meter, check for continuity between relay harness terminal 8 and ECM harness connector terminal 108.

Continuity
Should exist.

8. Using a ohm meter, check for continuity between relay harness terminal 5 and ground.

Continuity
Should not exist.

9. Using a ohm meter, check for continuity between relay harness terminal 4 and ECM harness connector terminals 25 and 12.

Continuity
Should exist.

For additional tests


If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, road test the vehicle to confirm that the repair has corrected the problem.
If the same problem reoccurs, it is possible that there is an intermittent failure of the component or the ECM. Check for looseness at all harness junctions and test for an intermittent failure.