jeffp1167

when it is jumped from the battery fires right up. But sometime can crank engine over for a minute and sometimes it will kick in other times it won't.

RetiredSFC 97

Does the pump run when you turn the key on? Otherwise it sounds like you may not be getting the required amps. Bad batt or Alternator. I would start with checking those two items.

jeffp1167

no does not come on when key is turned on, also does not come on while cranking. Then after a minute of cranking it sometimes comes on.

vetteoz

Maybe OP switch is faulty and not closing at intended 4psi when cranking
Check OP switch for correct operation


Check pump relay / connections and wiring.
Check relay ground
Check relay (terminal C ) for 12V signal from ECM when key turned on ( 2 sec only )

jeffp1167

Also forgot to mention when it does finally start it stays running for long periods of time, but when shut off it goes back to doing same thing.

Churchkey

Pull the connector off the oil pressure switch & install a jumper wire in the connector. Turn the key on.

Fuel pump running?

yes = fuel pump relay or wireing problem.

No = fuel pump or wireing problem.

geoharrison

I had a very similiar if not the same problem.As time went on I had to crank longer and longer to start. Finally thru a code which indicated fuel pump relay or oil pressure switch,it was the relay.If you turn the key and you don't hear the pump you either have a bad relay or oil pressure switch. There is a pin on the diagnostic connector you can put 12 volts to to test the fuel pump itself.

jeffp1167

Well, I know the pump is fine since like I said earlier when jumpered the car fires right up & fuel pressure immediately jumps to about 45psi.

vetteoz

No need to turn key on
Org wire to OP switch is hot all the time ( see diagram above );
pump will run full time with jumper in.

vetteoz

Key on only gets the ECM running the pump ( through the relay ) for 2 sec
Switch doesn't come into play until engine is cranked over

RetiredSFC 97

It's leaning to bad realy or OP switch

j-wireman

I love this Forum. I just learned something. Thanks, guys.

Mike
'90 'vert

jeffp1167

Today it seemed to start fine, so maybe it is just a relay acting up.

RetiredSFC 97

I'd still check the batt and alternator, just cuz

Frizlefrak

Correct. There is massive misinformation on this out there.

When you turn the key on, the ECM energizes the fuel pump via the relay for two seconds, or continuously during cranking. The oil pressure switch acts as a secondary path to start the car in the event of a relay failure, and will close the fuel pump circuit at approx 4 psi during cranking. The oil pressure switch NEVER COMES INTO PLAY if the relay is functioning correctly, and it won't shut the pump off in the event of a drop to zero in oil pressure. It is not a failsafe to save the engine.

A dead relay will usually result in long cranking times until oil pressure is built. If you don't hear the two second prime, and the car won't start with long crancking, BUT you can energize the fuel pump through terminal G on the ALDL and the car will start, you have a dead relay and oil pressure switch.

{whew}

Refer to the wiring diagram above. The relay and oil pressure switch are wired in parallel, not series.