Expert: Van - 1/29/2006

Question
I have a 1997 Z71 Chevrolet 350. It sometimes has to spin alot before cranking. I replaced the fuel pump. I have not noticed a difference if the engine is hot or cold. Almost every moring it has to spin alot before cranking. The fuel pump does not buzz when I turn the ignition on, but as soon as it fires I hear the pump running and it runs for a couple of seconds after I shut the engine off. I am currently replacing the plugs and installing a new fuel filter. Any advice would be appreciated.

Answer
Hello Randy,
The fuel pump is normally operated by a relay. But there is a backup system that also sends voltage to the fuel pump, and that is an oil pressure switch. As soon as 4PSI of oil pressure builds up, that switch closes and the pump is connected with both the oil pressure switch and the relay.
It sounds to me like your relay is not working, and yours is operating completely on the oil pressure switch circuit.

The relay is operated by the ECM, which is supposed to turn it on for two seconds when the key is turned to run. Then, as long as there is a crank signal, meaning the engine is turning over, it will keep the pump running.
I wouldn't condemn the crank sensor, since you said it doesn't even run the two seconds. That first two seconds should happen weather there is a crank signal or not.

So...we are looking at a bad relay, a loose connection at the relay or ECM, a blown fuse/fusible link,(although the older trucks used the same fusible link for oil pressure and relay circuits), or possibly a bad ECM, which I doubt.
I would think probably the relay.
But check for blown fuses also.

Van