Fuel Pump Relay: Description and Operation

Fig. 4 CIS-E System Components:

The fuel pump relay controls various functions of the CIS-E system such as fuel pump operation, maximum engine speed limitation, oxygen sensor heater supply voltage, cold start valve activation, transmission (automatic) kickdown cutoff, and fuel pump cutoff in the event of an interruption of the ignition signal (TD) to the fuel pump relay.
An input from the ignition control unit provides a TD signal which energizes the fuel pump relay during starting or with the engine running. The fuel pump relay is also activated briefly when the ignition is turned to the run (ON) position. If no TD signal is received or the engine reaches maximum RPM limits the fuel pump relay will then switch the pumps off.
Cold start valve activation depends on coolant temperature and cranking speed signal. Voltage supply is via the fuel pump relay. The length of time during which the starting valve injects fuel is dependent on the coolant temperature. If the engine starts before the cold start valve completes its cycle, cold start injection is cancelled.
If the fuel pump relay receives a certain frequency signal corresponding to the maximum engine RPM, the contact between circuit 30 and 87 is interrupted and the fuel pumps are turned off.
Activation for the A/T kickdown solenoid valve is routed via the fuel pump relay. The circuit to the kickdown solenoid valve is interrupted approx. 200 RPM prior to maximum engine RPM cut-out and the transmission shifts to the next gear. This will assure that shifting occurs prior to maximum engine RPM cutout.

Fuel Pump Relay Terminal Designations:

The fuel pump relay has been modified to include a separate oxygen sensor heater control circuit.

1st VERSION

As of December 1989 the fuel pump relay and harness contain an extra terminal for the O2-sensor heater identified as 87H. Activation of the heater circuit occurs as on previous relays, since the extra terminal 87H is connected by a bridge with the terminal 87 of the fuel pump relay.

2nd VERSION

As of January of 1990 the bridge between circuit 87 and 87H has been deleted. The fuel pump relay electronics have been modified to turn on the O2-sensor heater at a coolant temperature of 68°F based on information from the coolant temperature sensor.