No cold start until oil PSI reaches 15~20

[GSTOY]

If the car has been sitting more than 8 hours, it will not start until it sees oil pressure. Once it starts, it's fine. It was starting fine after sitting, but now doesn't even want to think of it. I have checked all grounds, and has a new fuel pump relay, but my hunch is either the ignition switch is worn out or the ecm, thoughts?

Steve

 

[Dabigguy]

There's a problem with your fuel system's power supply. May be a bad relay.

http://www.turbobuick.com/forums/ge...10-no-oil-pressure-switch-car-still-runs.html

 

[TurboBuRick]

Sounds like you lost the fuel pump signal in the ecm.

For now you can run a jumper wire in place of the relay.

 

[Nick Micale]

Could be a pump problem, or a wiring problem?

My plan would be to jumper the pump with the wire behind the alternator before starting the car after sitting 8 hours.

If the pump runs and the car starts right up when the jumper is connected, probably a wiring issue.

If the pump is bad, it may take a while to start the engine, and by that time you would have oil pressure.

 

[IrvJr]

Sounds like you lost the fuel pump signal in the ecm.

For now you can run a jumper wire in place of the relay.

X2, happened to me. Replaced the ecm and worked fine.

 

[GSTOY]

Pump and relay are brand new and I can jump off the back of the alt and have fuel pressure. Guess I need to locate a ecm.

Steve

 

[TurboBuRick]

Pump and relay are brand new and I can jump off the back of the alt and have fuel pressure. Guess I need to locate a ecm.

Steve

ECM is in the passenger kick pannel.

 

[garyk1970]

my fuel pump relay was bad and it saved my engine....i broke the timing chain/cam/cam sensor and the car instantly shut off......stopping debris from flowing in the oil throught out my engine.
I'm leaving mine that way.....
if it takes a few extra seconds to start,why not leave it alone? just a thought...

 

[GSTOY]

UPDATE:

Found the problem. The +12V coming from the pink/black wire was non existant to feed the 12v from the relay to fuel pump. ECM is working by sending the momentary 12v to activate the relay. Rick sent me the wiring prints and found it from there. Guess I have a bad wire from the oil pump sender to the relay so I found another 12v supply and it fixed the problem.

Appreciate the help guys!!
Steve

 

[GSTOY]

Gary,

Just FYI....after looking at the schematic diagram of this circuit, the only purpose of the relay is to prime the fuel rail to get the engine started. The relay is only energized momentarily, about 2~5 seconds, from a 12volt supply coming from ecm with key on. Since the engine should be running now, the contact on the oil pump sender keeps 12volts to the fuel pump because it closes the contacts on the sender that send the 12 volts to the pump. So if you lose oil pressure, you now lose the 12 volts to the fuel pump.

Steve

 

[Otto J]

This cannot be how this works, I unplug the factory sender all the time when installing a gauge abd have never had any starting/running issues with fuel pump.

I believe the oil pressure switch is a back up IF the fuel pump relay does not work.

IT WILL NOT shut down the fuel pump if you lose oil pressure.

 

[GSTOY]

Interesting Otto. I didn't check after the engine is running if the ecm sends the 12 volts to the relay, so I guess I stand corrected. Sorry. Here

I thought I was on to something, because in a way it would make sense. Why would the ecm hold a normally open relay closed all the time when the engine is running when it could just do it thru the oil sender unit and serve double duty to protect the engine so that if you didn't have oil pressure, the fuel pump wouldn't be energized and the engine wouldn't run.

My apologies for confusing anyone.

Steve

 

[Dabigguy]

The oil pressure switch and the relay work in parallel. If one fails, the other is a failsafe. The link I posted eariler explains......http://www.turbobuick.com/forums/ge...10-no-oil-pressure-switch-car-still-runs.html

 

[Blazer406]

ECM is in the passenger kick pannel.

LOL

I don't think he meant literally... in his car...... I think he meant that he needed to find a good used one to buy.... LOL

 

[garyk1970]

That's right the oil sender is back up..that's why it saved my engine....all this is good info for future searches.

 

[RmvBfrFlght]

Interesting Otto. I didn't check after the engine is running if the ecm sends the 12 volts to the relay, so I guess I stand corrected. Sorry. Here

I thought I was on to something, because in a way it would make sense. Why would the ecm hold a normally open relay closed all the time when the engine is running when it could just do it thru the oil sender unit and serve double duty to protect the engine so that if you didn't have oil pressure, the fuel pump wouldn't be energized and the engine wouldn't run.

My apologies for confusing anyone.

Steve

The ECM is a bit tricky about how it controls the fuel pump relay. There is the 2-second key-on prime via the relay. Then, once the ECM receives distributor reference pulses (DRPs), it will then enable the relay.

Once DRPs stop it takes 2-seconds for the ECM to then disable the relay.

So, key-on, engine-off, relay is activated for 2-seconds. A short crank leaving key-on, engine-off, and the relay is activated again and times out after 2-seconds. When the engine is running a DRP is received every crank sensor slot on the shutter.

So the pump relay stays active.

There is a small transistor in the ECM that provides +12 volts to the relay. It is easy to pop this transistor while troubleshooting. They will also pop for no apparent reason along with when the relay coil starts to short out (go bad).

Easy to replace this transistor. Can use a 2N2907 or PN2907 (PNP). Open the ECM ('7148), remove the upper board screws and fold the upper board over to access the lower board.

In the center of the lower board are two small transistors (TO-92 case). One is a little taller then the other. That is the one that pops. Just unsolder it and insert the '2907 in the same direction (using the flat side as the direction).

Carefully put the ECM back together and you are go to go.

RemoveBeforeFlight

 

[garyk1970]

The ECM is a bit tricky about how it controls the fuel pump relay. There is the 2-second key-on prime via the relay. Then, once the ECM receives distributor reference pulses (DRPs), it will then enable the relay.

Once DRPs stop it takes 2-seconds for the ECM to then disable the relay.

So, key-on, engine-off, relay is activated for 2-seconds. A short crank leaving key-on, engine-off, and the relay is activated again and times out after 2-seconds. When the engine is running a DRP is received every crank sensor slot on the shutter.

So the pump relay stays active.

There is a small transistor in the ECM that provides +12 volts to the relay. It is easy to pop this transistor while troubleshooting. They will also pop for no apparent reason along with when the relay coil starts to short out (go bad).

Easy to replace this transistor. Can use a 2N2907 or PN2907 (PNP). Open the ECM ('7148), remove the upper board screws and fold the upper board over to access the lower board.

In the center of the lower board are two small transistors (TO-92 case). One is a little taller then the other. That is the one that pops. Just unsolder it and insert the '2907 in the same direction (using the flat side as the direction).

Carefully put the ECM back together and you are go to go.

RemoveBeforeFlight

excellent infomation sir.

 

[ttaowner]

good info