Trog

Anyone replace the pressure switch for fuel system shutoff lately?

Any thoughts on aftermarket replacement Vs Mr. Goodshaft?

Think mine is getting lazy on shutdown as fuel pump runs for a second+ after keying off.

Will prob. replace the gauge sender while I'm there at the same time. It is tight in there & will prob have to pull dist. cap to work.

TIA as always!

bogus

I would bet it's the relay itself.

that switch only helps the engine start if the FP relay won't fire. It will not shut the engine down.

CentralCoaster

The pressure switch is for keeping the fuel pump on. It's a backup in case the relay fails.

$7.50 for ac-delco.

The sending unit though, is a $30 part. You won't save much by getting the vatozone junk. To see if the pump is being powered by the oil pressure switch and not the relay... (such as after shutdown with a sticky oil pressure switch) run a test light from ALDL G (lower left) to ground.

It'll light if the pump is on and the relay is off.

Morley

That is normal for the pump to run a few seconds after you shut the engine off.

mseven

Yep, distr. is in the way, easier to pull the distr. to get a wrench on those switches. On the 90, the smaller one is pressure switch/sender other is sensor.
When I bought these, GM parts /description was, that switch (sensor m-f/pmp if I remember) is supposed to monitor oil pressure and when low pressure occurs while running (don't know reading) to allow fuel shut down as, to not hurt the engine. (supposed to not instantly shut down).
I replaced both because I was getting a leak there, and had to put a different extension and 90 to clear aftermarket intake. The original allum. 90 from the block, and extension are no longer available. hope this helps

CentralCoaster

It's a 4 psi normally open switch.

86PACER

Vatozone.

JAKE

I've seen posts going both ways on; some believe it'll cut off the fuel pump and others say it won't.

I've yet to come across anything in any of the manuals that say low or no oil pressure will cause the switch to turn off the fuel pump.

If you could post a source for that happening, I'm sure we'd all appreciate and like to see it. May well settle this once and for all.

Jake

CentralCoaster

It's already been settled, just not everyone got the memo. I think the myth that it functioned as a kill switch was perpetuated by Gordon Killebrew. The book clearly states otherwise.

Trog

Thanks everyone, I'll be running a few tests over the next couple of evenings. I just upgraded my intank pump to a Racetronix w/ power harness/relay & in prep. for a procharger in a few months also installed the aux. pump behind the license plate. It could just be the extra pump noise that I'm hearing now & don't remember hearing the stock run after the key off.

CFI-EFI

As normally interpreted, that is not correct. Only the word "ALLOW" that I put in bold, saves that statement from being totally false.

The fuel pump has two, independent sources of power. If someone doesn't believe that they can check both the circuit description and the schematic in the factory service manual. The oil pressure switch is a N.O. (normally open) pressure switch with an approx 4 psi trigger, as stated above. When the oil pressure at the switch is ~4 psi or more, the switch is closed and 12 volts is fed to the fuel pump. Besides the initial 2 seconds after the key is turned to the "ON" position, when the ECM receives pulses from the distributor that indicate the engine is turning, the ECM closes the primary circuit of the fuel pump relay, sending 12 volts to the fuel pump. IF the engine stops turning AND the oil pressure drops below ~4 psi, the fuel pump should stop running. The engine stopping turning or low oil pressure alone won't remove the power from the fuel pump. It takes both.

The quickest most revealing test, of either the relay or the switch, is to disconnect the other, preferably while the engine is running. If disconnecting the relay kills the engine, the oil pressure switch isn't doing it's job. It doesn't have to be a bad switch. It could be the wiring, but you've narrowed it down. The same is true if you pull the wires off of the switch. If you have a condition where the fuel pump runs on, pull the wires, first off of one, then off of the other, before you start replacing good parts.

RACE ON!!!