Borrowed from an old thread but it may help....

"When you turn on the ignition switch the ECM turns on the fuel pump relay for 2 seconds. This applies 12 volts to the fuel pump which pressurizes the fuel rails in preparation for starting. The reason it only runs for 2 seconds is to keep the fuel pump from running continuously if you turn on the ignition but don't start the engine. If you turn off the radio and A/C fan you should be able to hear the fuel pump run for 2 seconds when you turn on the ignition. The ECM will turn on the fuel pump when it sees reference pulses from the distributor. This will happen when the engine is cranking or running.

There is a backup for the fuel pump relay. This is the oil pressure switch, which applies 12 volts to the fuel pump when it sees more than 4 - 6 PSI (don't remember exactly) of oil pressure. It will see this much pressure when the engine is cranking.

If you are experiencing long cranking it could be because there is a problem with the fuel pump relay circuit and the oil pressure switch is taking over. The way to see what is really happening with the fuel pump is to put a fuel pressure gauge on the fuel rail.

This switch is located on the back of the block next to the distributor. There were two versions. The early one has a separate oil pressure sender (for the instrument panel gauge) and the oil pressure switch. The sender has one terminal and the switch has two. Later on GM combined the two into one sender/switch unit."

 

If its just cranking and cranking, go through the fuel system and check it out. Apply 12V to terminal "G" (i think its G, going from memory) of the ALDL to see if you hear the Pump turn on. Could be the relay, could be the pump, can be the oil pressure switch.

 

If the oil pressure switch is giving a faulty reading, which he stated, isn't it possible it is just a bad oil pressure switch.

 

so car starts are no?

you say when car starts it goes up to 450psi? or kpa? check that your switch is not on kpa. 450 kpa is 65 psi.

then you say car won't start.

 

In-car reading is via the sender, the switch is separate. So long as you have any oil pressure the switch should allow the pump to prime up if the pump relay itself fails.

But it will not cut the engine off if you suddenly lose all oil pressure.

 

I should have said sender (sensor) but I believe VT3 had the correct answer as to why it is reading high, sounds like switch is on metric. That still does not explain why it won't start though.

 

grab a fuel pressure gauge and report back if you hvae pressure while starting.