Where to look for what tells pump to prime

[badgto]

1994 V/6 with automatic, truck runs if you put 12 volts to feed side of fuse. In other words turn the key and pump don't prime or run. No voltage found on either side of fuse in key on. But hook 12 volts to feed side pump runs and truck runs. I need to find what is suppose to tell pump to prime.

[ChevyTech]

The ECM controls the fuel pump relay.

The truck has a fuel pump relay that supplies power to the fuel pump when:
- Anytime the ECM receives a distributor reference pulse. (Engine running / engine cranking)
- The key is turned on engine not cranking – relay applied for 2 to 20 seconds (most trucks 2 seconds), depending on emissions equipment. Trucks over 8500 GVW and some other vehicles have and electronic Fuel timer module that allows the pump to run up to 20 seconds.
The key must be turned off for a certain amount of time before it will prime the system again when turned back on.

There will only be power to the fuel pump for a few seconds when you first turn the key to the on position. If you are turning the key on then walking around the vehicle testing for voltage to the fuel pump circuit there will be no voltage and should not be power to the pump.

The ECM should store a code 54 if the fuel pump relay fails.


When the engine has oil pressure a redundant circuit supplies power to the fuel pump. This circuit goes through an oil pressure sensor/sender. This circuit is independent of the fuel pump relay.

Check the computer for a code 54. This can be done without a scan tool on your 1994.