mike3605

2000 5.7 Z28 will not start ... cranks and cranks and cranks, but nothing. Issue is that my fuel pump is not getting power to prime.

I turn my vehicle to on (without starting) and the security light goes out, so everything is pointing to a non-vats issue (i believe?).

I replaced my fuel pump (needed to do anyways), metered wires from fuel pump to relay, relay to pcm, fuse to relay (all good), checked my fuel pump relay part (good) but then noticed when i turn my key, i was not getting the power to prime my fuel pump ... the wire from the PCM to the relay was good ... so something wasn't telling the relay to open. I replaced my PCM, and it still is not priming without a jumper. I can jump it by taking the relay out and using a wire, and the fuel pump primes and receives power and then the car starts for a few seconds then dies (because no fuel).

My question is what in the world "tells" my PCM to give it power to open up my ignition relay?

My next step is to just cut the wire from the PCM and steal power from another source that will allow power when i turn my vehicle on (that way the pesky CO emissions wont know).

Any help is appreciated as I would like to fix it correctly.

wph351

iTrader: (3)

Did you check the ground side of the relay? It won't close if it's not grounded.

mike3605

i did; it was good ... i wouldn't be able to jump it with the by-pass relay wire to get it to start if it was bad because i'm pulling the relay, and putting a piece of wire between the two connections to engage the fuel pump.

wph351

iTrader: (3)

The ground side of the relay would become irrelevant once you bypass the relay.

wph351

iTrader: (3)

The pcm sends 5v to close the relay. Are you not getting the 5v?

mike3605

the relay itself, yes ... but i am pulling it out of the equation and jumping it so it becomes irrelevant

the fuel pump primes and engages when I do this

mike3605

I'm not ... so I was wondering what tells the PCM to send that?

(The wire is good (metered a loop from PCM to relay, and i get a reading ... so the wires are all good)).

mike3605

I should also note I have used other relays "just in case" ... and it's safe to say it's not fuel pump, wiring, or relay issue ... everything from the PCM forward is good (including the PCM .... i got a new one!)

wph351

iTrader: (3)

Once it recieves ign 12v it will prime, then kick on and stay on once rpm is recognized. Maybe check the 12v ign. Inputs to the pcm?

mike3605

so the ignition from the PCM leads me to the crankshaft position sensor ... any ideas where that is located?

wph351

iTrader: (3)

Beside the starter.

wph351

iTrader: (3)

Your crank sensor won't cause a non prime situation.

mike3605

man ... i am out of ideas with this one besides just bypassing the PCM signal, and finding a place from the ignition circuit to jumper in a power line to the fuel pump relay .....

wph351

iTrader: (3)

Could you run me through the method you used to check for 5v at the relay from the pcm?

mike3605

stuck the multimeter on the fuel pump relay ctrl wire (dk grn/ wht) and not receiving any power indication with ignition on ...

used same wire from relay (that was confirmed to be fuel pump relay) and created loop to get a reading at the PCM plug ... so the actual wire was good, but the PCM is not sending the signal to close that relay

wph351

iTrader: (3)

Where did you ground it? Did you check while turning key? Just making sure nothing was overlooked.

wph351

iTrader: (3)

If the pcm is truly not sending a signal, my next move would be to ensure it is receiving all of its 12v ign. Inputs.

mike3605

grounded it from a known ground that works; yes checked it while ignition on position, and turning key position - nothing

mike3605

from the wiring diagram on what sends the signal to prime that fuel pump, ends at the PCM with the fuel pump relay control ... any ideas where to start with the ignition?

wph351

iTrader: (3)

Check for 12v at these while turning key to on...Blue connector pin 2, this is a 12v reference but I'm not sure for what. Also blue connector pin 19.