OK, I picked up a 92 Z28 with the 305 TPI, it wont start - now there's a suprise huh?

Anyway, i suspect some part of the fuel pump system becuase when i turn the key, I don't hear the fuel pump prime.. I have checked the 20A fuse near the battery, i have checked all of the other fuses in the fuse block, and i have replaced the fuel pump relay but still no noise out of it..

There seemed also to be quite a few fuses missing from the fuse block so i put in new ones just incase as i dont know which fuse runs the pump.. My Haynes says it i labelled FPump but i think that is TBI only.. Using a multimeter i checked at the relay pinouts so i know I have 11.5V there so i think the fuse is good right? I have pulled back the carpet in the trunk and found the wires that run to the pump, they look OK at this point..

My question really is, can i just cut these wires here and check to see if i still have voltage after the relay near the pump? I dont know how else to take a voltage reading after the relay without cutting the wires near the relay or dropping the tank... Is there another way thta i just dont know about? I'm pretty sure my mulitmeter wont read the voltage through the insulation on the wires so cutting or stripping is the only option right?

Any help is appreciated, sorry for the long post..

PS.. I have searched heaps so please just help

 

i found a plug under the car that runs to the f/p. you can check for power there to basically eliminate everything short of the pump itself. it was up above the differential so you might have to let the back tires hang in the air to get to it. put the car on jackstands at the subframe connections and go from there

 

Hey thanks, the rear is already up on the stands and i can see where the wires come through from the interior but short of having go-go gadget arms, I'm not sure i would be able to disconnect the connector and get my multimeter on there.. i ill give it a go.. thanks for the tip.

Cheers,
Richard.

 

Have you checked the oil pressure sending unit? Current runs directly through the OPSU to the fuel pump... a bad OPSU = no fuel pump. A bad OPSU can also mean a fuel pump that runs constantly, even with the key out. Try checking that too. You can check by pulling the fuel pump relay from it's wirepack and making a direct connection on the wirepack, I think it's the orange wire and brown wire (check a wiring diagram to verify colors). Make a short wire with blade connectors on each end and run between the two - this would make the fuel pump run with the key on.

 

OK, i checked at the connection above the diff and found only 8v on the purple wire, the grey wire had 0. Looking at the wiring diagram in the Haynes, it looks like the grey wire is the one that should supply voltage to run the pump, the purple seems to be for priming only?

Does it still sound like it could be the OPSU? I will do a search on that and see hwat i can find

Glad this isnt my only mode of transport

 

The auxilliary oil pressure switch is NOT in series with the pump relay, but in parallel. It is only there in case the relay fails:



You will ONLY get the pump relay to operate for two seconds after the ignition is first turned on, and again after the ignition has been off for at least 20 seconds, then turned back on.

I'd suggest you do the diagnostics at the relay, and see if it is actually operating. All the wiring you need to check is there, including the wire directly to the pump.

The above circuit diagram is from an earlier TPI, but the oil pressure switch is wired the same on later TPIs. Your pump power wire is gray. The purple wire is for the fuel level gauge.

 

Hmm, acording my Haynes it is in series - u sure thats not the wiring diagram for 89 and earlier models? thats kinda what it looks like to me?

Anyway, i do agreee about checking the voltages after but near the relay but that takes me back to my original qestion of how? Do i just strip the wires just below the Relay? I dont know how else i would be able to take readings with the relay connected????

Cheers,
Richard.
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Sorry, just re-read what you wrote, yes it is earlier TPI's, looks like they are wired in series on the 90 and later models.. (although i could be wrong as i am no automotive electrician )... anyway, thanks for the tip on the purple wire, i guess 8V means 3/4 of a tank

Cheers,
Richard.

 

I have never seen a GM oil pressure switch wired in series other wise the pump prime would not work. The eaiset way to check for the relay working and the wiring is to use a test light and some one to turn the key on and crank the engine over. I prefer to use a test light on fuel pump circuit due to past misdiagnostics. A corroded spot in the wire may show 12v with a digital voltmeter but not have the ability to carry enough amps to run the pump. If you find you don't have power at the connector under the floor you should move upto the relay. To check the output of the relay use a straightened paperclip to probe the output of the relay between the wires seal and the wire being careful not to damage the wires insulation or the seal. As for the 8v that would be the voltage drop arcoss the coil in the gauge. Mike

 

OK, i applied power directly to the pump via the connector under the floor using a battery booster and i heard it turn over - it just turned over real, real slow... i guess it is shot..

 

Well who would of thought it... I left the battery charging this afternoon as it was almost dead, i went back in to tidy up a bit and figured i would just give it a quick turn over.. well would you belive it fired! It didnt idle but would stay running as long as i gave it a little throttle but stalled out as soon as i let off the gas pedal... anyway, at least it runs and i did actually make some progress today

I guess the fuel pump could still be shot since it didnt idle but i havent read any articles on "won't idle" i only got as far as the section on "won't start"

Thanks everybody for your help today

 

Sounds like a dead pump have someone crank it while you tap on the tank with a rubber mallet. This some times gets them going again for a short time but makes them easier to move until you change the pump.

 

good luck changing that pump if you ever need to.

 

What color is the fuel sending unit for a 89 iroc camaro and a 87 trans am I am trying to interchange the feul sending unit thanks