1992 GMC Vortec 4.3l injection system...

Strange that you can't find anyone familiar with the CPI, given that it's been around for over 10 years and carrys a rather poor reliability history.

When you say that you can't find the pressure regulator, do you mean that you can't find one to buy or that you can't locate it on the vehicle?

Known frequent CPI problems; Low fuel pressure Leaking injector poppets Plugged injector poppets Leaking fuel pressure regulators Cracked fuel nuts (the plastic fuel lines inside the manifold plenum) Broken or ruptured fuel pump 'pulsator.' (the pulsator is the rubber link between the fuel pump outlet and the steel line that exits the sending unit.

Discerning between these different problems required dilligent diagnostics with the proper tools; fuel pressure gauge, scan tool, DVOM, labscope, etc. But the first step is always; what is the fuel pressure, key on engine off and key on engine running.

Thanks for the reply Neil!

From what i have deduced, i can hear the fuel pump running when the motor is running. But when i get someone to key the ignition before starting i dont hear anything. (it should run for 2 seconds)

Also, it seems the pump only comes on when the oil pressure switch is triggered (after 5 seconds of cranking) and then the truck starts.

I am led to beleive there are 2 relays to control the fuel pump.. One controlled by the ignition and another interlocked with the oil pressure switch... But i am at a loss to find where they are hidden so i can check the circuitry..

any help?

-One- fuel pump relay and given what you describe, you're on the right track in suspecting it. The fuel pump relay is wired in parallel with the oil pressure switch. The 92 Typhoon (VIN Z) I worked on last week had the relay mounted to the firewall just above and slightly to the passenger side of the distributor, there were two relays mounted together to a tin bracket (had to move 'em to R & R the distributor cap and rotor). Somewhere under the hood breaking out of the wire harness (possibly near the wiper motor) is a fuel pump test lead, probably a single gray wire with a green plastic connector, you can stab this lead with a test light connected to ground, turn the ignition on and see if the light lights to test power out of the relay to the fuel pump.

thanks neil.. i have sorted the problem out...

i swapped the oil pressure-fuelpump relay with the ignition-fuelpump relay and the truck starts up perfect now, with the relay running for 2 seconds when the ignition is keyed.. unlike before when it would only start when the oilpressure was brought up (by cranking)

my question is.. why would gm have 2 seperate relays in parallel feeding one fuel pump on the same circuit....

Excellent!

Redundancy in the circuit. I suspect that in some committee meeting waaaaay back in 1978 or so, some engineer won a concession over the bean counters.

I admire some of the things GM does in their electrical systems design, this is one of them.

I'm not sure if that has happened since. Bob

I'm pretty sure that that engineer was taken out and shot, hung by the neck and had his throat slashed.

Along with the bean counters that let him prevail. Bob