There are three ECM controlled relays which are an integral part of the TPI system.

Fuel Pump Relay

The fuel pump relay is controlled by the ECM and acts as a remote switch to route power to the electric fuel pump. A relay is necessary in this application because most high pressure fuel pumps can draw up to approximately 10 amps of current. The fuel pump relay is backed up by an oil pressure activated switch which maintains +12 volts at the fuel pump power terminal as long as the engine has oil pressure. This will allow the vehicle to start and continue running in the event of a fuel pump relay or partial ECM failure. This oil pressure activated, fuel pump control switch is mounted (depending on the year and model), either in a threaded port on the left side of the engine block (just above the oil filter), or in conjunction with the oil pressure gauge sending unit in a fitting behind, and to the left of, the distributor assembly.

The first indication that the fuel pump relay has failed and that the back-up switch has taken over fuel pump operation, would be extended cranking time before the engine eventually starts, accompanied by an illuminated Check Engine/Service Engine Soon light.

Mass Air Flow Power and Burn-off Relays

The other 2 relays are the MAF power relay, and the MAF burn-off relay. These twin relays supply current:

In GM installations these 3 relays are usually mounted in a group with the ESC module on the cowl, or inner fender panel. In our applications, we suggest mounting these relays along with the ESC module in the area of the ECM (eg underneath the passengers seat), to eliminate engine compartment clutter and ease the wiring process.

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