fuel pump used to tun for an instant before starting

[CS99]

fuel pump used to turn on for an instant before starting

My fuel pump used to run for an instant before starting. It doesn't do this anymore. I think this is causing my hard starting, but when it does start the car runs fine. I can shut the car off after its been running and it will start right back up. I am running a MaxEffort chip but I don't think it would have to do with this problem. Any ideas?

 

[OKTurbo]

The fuel pump gets power from the FP Relay....once the car is running the oil pressure switch will also power the FP.

Since it doesn't prime during startup when the ECM tells it to I would suspect the fuel pump relay (on the passenger side inner fender).

Cranking it during start-up may spin the motor enough to close the oil pressure switch and give the fuel pump power....hence the hard starting.

John

 

[Low Budget]

The ECM will do it before it's running under the right circumstances.

The fuel pump relay is the primary system to power the pump.

If it fails, the ECM will power it directly, but only when it sees
7 1/2 psi of oil pressure. (Reason enough to not eliminate the oil pressure switch.)

That is why it turns over so long before it starts.

Replace that relay or clean the connections...whatever it takes to get the relay up again.

This will fix you right up.

 

[gn85]

Originally posted by Low Budgit
The ECM will do it before it's running under the right circumstances.

The fuel pump relay is the primary system to power the pump.

If it fails, the ECM will power it directly, but only when it sees
7 1/2 psi of oil pressure. (Reason enough to not eliminate the oil pressure switch.)

That is why it turns over so long before it starts.

Replace that relay or clean the connections...whatever it takes to get the relay up again.

This will fix you right up.

I don't beleive the ECM has anything to do with giving power directly to the fuel pump by way of the oil pressure switch. As I recall, this is a direct circuit from the oil pressure swich to the fuel pump. I don't have the wiring diagrams in front of me, but I'm fairly certain that is how it works.

As for the ECM, it will send a signal to activate the fuel pump relay for two seconds or until it gets an ignition reference. However, sometimes if the car is cranked, not started then cranked again in a short period of time (I think within 30 seconds) the ECM will elect to skip the 2 second priming until it receives an ignition reference.

As said before... get your relay fixed and you should be back in business. Is this car hot-wired?

 

[CS99]

A BIG THANK YOU!!!!

Thanks, I unplugged both relays on the pass side fenderwell and then plugged them back in and everything works. There is a bunch of hard and dirty grease in the connectors so I will clean this out and add new dialectric grease and see what happens.

 

[Ken Cunningham]

Re: A BIG THANK YOU!!!!

Originally posted by CS99
...There is a bunch of hard and dirty grease in the connectors so I will clean this out and add new dialectric grease and see what happens.

That hard and dirty grease is probably the stuff that Buick put in from the factory. I know it's hard to believe when you see that awful stuff, but Buick actually wanted it there.

 

[TurboJim]

Originally posted by Low Budgit
If it fails, the ECM will power it directly, but only when it sees
7 1/2 psi of oil pressure. (Reason enough to not eliminate the oil pressure switch.)

Hahah, close, but no cigar. The oil pressure switch is wired after the relay in the FP feed circuit. When the oil press switch closes IT feeds the pump

The ECM will prime, then turn the pump on when it gets crank pulses.

 

[OKTurbo]

Actually Jim,

Technically speaking (after looking at the wiring diagram) the FP relay and the engine oil pressure switch are in parallel. So, power can come from either the relay or the oil pressure switch.

http://www.gnttype.org/techarea/images/wiring.gif

The diagram says (for the oil pressure switch) "closed with normal oil pressure". In other words, once the oil pressure is high enough (not sure what the mystery pressure value is) it will supply power to the FP by itself.

The FP relay and the oil pressure switch are independent of each other. The computer tells the FP relay when to close (turn on the pump). We know that when you turn the ignition switch the computer will close the relay for a second or two to prime the pump. After that, I'm not sure what the computer's rules are for the FP relay.

I'm really just splitting hairs here with the wording, but I was curious how it actually was wired so I looked it up.

The bottom line is that (like it's already be said above) the primary suspect is the FP relay.

John

 

[gn85]

There must be an echo in here...

Originally posted by TurboJim
Hahah, close, but no cigar. The oil pressure switch is wired after the relay in the FP feed circuit. When the oil press switch closes IT feeds the pump

The ECM will prime, then turn the pump on when it gets crank pulses.

Very good Jim.. I can see you beat me to saying it. *sigh*

 

[Low Budget]

CS99

Glad you're under control. That's after all the important thing here.

 

[TurboJim]

Re: There must be an echo in here...

Originally posted by gn85
Very good Jim.. I can see you beat me to saying it. *sigh*

I'm just trying to be as good as you Chris....