Well, I'm finally getting around to getting my '88 Camaro SC up and running again after sitting on the driveway for close to 2 years (it has been run a couple of times in between, but not driven). After jump-starting it (and now after getting a new battery in it), I noticed that the fuel-pump doesn't cut-out like it's supposed to before starting. That is, when I turn the key to the "run" position, usually the fuel pump will prime for a few seconds but then cut out. Instead, it just continually primes. For what it's worth, the car does run but very badly. I have to give it some throttle at first or it will die if it's not warm. Plus, it pops through the exhaust esp. when in gear and I give it even light/moderate throttle. I'm wondering if the fact that the fuel pump keeps priming is indicative of a fuel-delievery problem, and hence why it's running like crap. Any ideas?

Fuel pump relay?

Where's that located again? I'll test it out.

maybe you're losing pressure in the system and that's why it continually runs... because it doesn't get up to pressure.

would also explain why it runs crappy and pops when under load.

start checking all your possible culprits... gascap? rubber hose that goes from the tank to where the metal lines start, fuel filter, the line itself, purge valve on the fuel rail?

who knows

I do. It is not due to the system's inability to achieve pressure. There is no pressure switch to sense or control that.

Low pressure could certainly cause some of the poor running symptoms, but won't cause continued pump operation. That's either a faulty relay or auxiliary oil pressure switch.

Oil pressure switch? What does that have to do with the fuel pump running?

(Not doubting ya', Vader, just curious because I wasn't aware of any such system on the 2.8L V6. )

The oil pressure switch powers the fuel pump after the engine starts.

Both the oil pressure switch, and the fuel pump relay common contact are connected in parallel to the same "Hot at all times" fused 12volts at the Battery.

If you removed the fuel pump relay the pump would run when the oil pressure closes the switch (longer cranking time.) keep the switch closed and the pump will run continuously with, or without the key period.
For this to happen with the fuel pump relay the relay contacts would have to be stuck together (basically a closed switch.)

If the Key is turned to "RUN" with the engine off, there's no oil pressure, and the oil pressure switch is a moot point.
The fuel pump relay is switching with the key (pump doesn't run in the off position) that leaves the ECM at fault because it controls the power to the fuel pump relay coil.
Let us know what you find.

Makes sense to me. So I suppose the purpose of the oil pressure switch is to cut the fuel pump (and thus stop the engine) if the oil pressure drops too low?

I'll check that relay out, but I need to figure out which one it is first. Hopefully my shop manual gives me some pointers on that.

On these threads some call it a myth. I'm going to run a couple of test to verify it actually kills the engine.


and


Put a finger on all 3 relays and have someone turn the key to "RUN" only one will click, that's the fuel pump relay.
On mine it's the relay in the center of the 3 located on the firewall behind the brake booster.

More likely stopping the engine when the oil pressure drops is a side-effect. There would be better ways of stopping the motor than shutting off the fuel pump, like inhibiting the injectors or spark.

It's not a side-effect (like taking a pill for a headache, and getting diarrhea) shutting down the fuel pump is what the oil pressure/fuel pump switch is designed to do just in case the operator doesn't notice the drop in pressure, or idiot light because he's too busy talking on his cell phone, or watching the lady in red.
Shutdown the fuel pump, motor stops no reference pulse to ECM = no injector signal. For safety reasons you don't want the fuel pump running with the key on/engine off, especially in an accident.

Here is the schematic:



Let us know what you find. Maybe your car is different than the 867,000 other ThirdGens built, and other 64,416,000 GM EFI systems built like this.

AFAIK, only Ford installed an inertia/momentum switch for fuel pump cutoff (the goofy steel ball/slider rail system). Oddly enough, the switch only works in a frontal crash, whereas Fords tend to blow up when struck from the rear. Perhaps the boys in Dearborn know that many of their customers are also the type of people that tend to drive into things, and wanted to preserve those customers as a market for replacement products.

Go figure...

I mentioned the oil pressure switch along with the relay, since those are the only two paths GM provided to power the pump.

An engine that hasn't been run for a while can have sludge in the sump, which could lodge in oil passages on cranking and prevent oil pressure from dropping as fast as it might normally. This would result in continued pump operation.