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

Multiport Fuel Injection Relay:

Failure of the Multiport Fuel Injection Control (MFI) relay could interrupt power supply to the fuel pump, injectors and ECM, resulting in a no start condition.

CAUTION: If battery polarity is incorrectly connected, the relay will be damaged.

Fig. 1 Relay Test:

COMPONENT TEST
1. Remove the MFI relay from socket.
2. Using jumper wires connect 12 VDC to relay terminals 5 (-) and 7 (+).
3. While connecting and disconnecting the negative jumper wire, measure the voltage at terminal 1 of the relay.
- With the jumper connected, battery voltage (12 VDC), should be present at terminal 1.
- With the jumper disconnected, 0 volts should be present at terminal 1.

Fig. 1 Relay Test:

4. Using jumper wires connect 12 VDC to relay terminals 6 (-) and 8 (+).
5. While connecting and disconnecting the negative jumper wire, check for continuity between terminals 3 and 4, and terminals 2 and 4, of the relay.
- When the jumper is connected continuity should exist (0 ohms).
- When the jumper is disconnected continuity should not exist (infinite ohms).
6. If the relay fails any test, replace relay
7. Check continuity between relay and ECM.
8. Check grounds.