What should the voltage be at the fuel pump on a TPI car? What should it be with the key turned on, at idle, and at WOT? I'm not getting any fuel pressure (only 25psi) and the pump only has 9 volts with the key on.

 

With a fully charged battery and everything working as it should. The voltage should equal battery voltage.

 

So, from idle to WOT voltage should be 12+ volts? Would having only 9 volts cause my fuel pressure problems?

 

Yes because the pump is not working at full power.

 

Excellent, thanks for the quick reply. I guess I need to re-wire to allow for 12 volts all the time.

 

How do you have it wired now? Are you by-passing the ECM and fuel pump relay?

 

I wouldn't re-wire because you'd be bypassing the engine's proctection circuit against loss of oil pressure. If that's not a problem then just tie together the 2 wires of the fuel pressure switch connector.

 

If your talking about the oil pressure switch cutting off power to the pump if oil pressure drops below 4 psi, that's a common belief, but incorrect. The oil pressure switch merely acts as a backup to the relay.

if you look at the diagrams, the power out from the oil switch is spliced into the power out wire from the relay. If the relay fails, the pump is powered by the switch, assuming 4 psi oil pressure.