Pump not priming

[Dented Dent]

I checked pump supplied voltage with key on and found 7mV, and 13.4V while cranking, I'm having a hard start problem and have replaced the pump, please help before I miss work

[Dented Dent]

Also this is a 1990 Fuel Injected 4g64

[tortron]

check the relays? possibly the are switched earth, so power is getting to the pump but the relay isnt switching and completing the ground

[Dented Dent]

So the main relay by the kick panel?

[tortron]

I think there should be an EFI relay and one for just the pump. possibly the issue (which i have seen in other cars) is that the fuel pump relay is not functioning. This means when you turn the key the pump wont prime. However the pump is able to get power through the EFI relay once the car is running, which i think is what you mentioned in another thread.

I dont have any experience with a stock mighty max, injected electrical system so im not sure where they will be located, but the symptoms match

[tortron]

Looking at this diagram
http://mmeierle.com/MPI24LCircuit-1.jpeg

you are getting power from the engine control relay, wire 2-BL (black and blue) i would start checking that wire.
you may also want to unplug the ecu a couple of times to clean up any dirty connections
Good time to check any fuel filters you have


I also see you mentioned you thought it might be the fuel pressure regulator. Once the pump is working, check to see that fuel is getting to the fuel rail. If it is and the truck still doesnt start, Pull the return hose from the Fuel Pressure Regulator and see if its wet with fuel after cranking the engine. If its dry, your Fuel Pressure Regulator could be faulty.

[Dented Dent]

I've found that the fuel pump primes occasionally and the engine still doesn't crank on its own without unplugging the fuel pump and plugging it in after getting started. I see a main relay by the right side kick panel. And the pump only primes for 1 second whenever it does, and when it does it still doesn't crank. Oil smells of fuel and lots of white smoke

[tortron]

OK, possibly there are other issues,
Were there any issues before you swapped the pump?
but i think for now you can focus on getting the pump working reliably.

First i would check all the fuses just incase

It sounds like it does, but just to check. The pump runs and pumps a good amount of fuel if you run a 12v jumper directly to it? The ground wire and connection is good?

When you turn the key to the on pos is there 12v to the pump? how about at the black and blue relay wire? is the relay clicking when switched to the on pos?
is there power to the relay box (looks like black and white wire) when key is in on pos?

[Dented Dent]

Pump works great when I jump it, and only 7.6mv when on but 13 when cranking, pump only primes occasionally, and I had issues cranking 3 days before changing the pump, I figured it was the pump since it had been whining pretty loudly. Before i changed the pump it cranks and cranks and cranks and cranks and EVENTUALLY it would fire, but eventually it wouldn't start at all so I changed the pump and plus it was due for change anyways

[pennyman1]

Did you check the ECM for bad caps? these truck can have all kinds of problems with bad caps.

[Dented Dent]

What do you mean by bad cap?

[Dented Dent]

Let me add a little information to my thread, I replaced pump and filter, and it's doing the same thing as before I changed the two. The pump primes for 1 second very rarely. If I don't unplug the pump it will NOT start, and after it starts and I quickly plug in the pump before it runs out of fuel it runs, but it smoke white smoke, misses on occasion, and the oil smells terrible of fuel, I'm scared to run the thing. All fuses are good and I checked grounds. And I can't find anything. Relays click when I switch the key off, and when the pump does prime I can hear a relay click off when finished and then it still doesn't start. No fuel in the pressure regulator and it holds a vacuum. I listened to the injectors and they're all clicking the same sound. I'm limited on tools since my toolbox was stolen. And when I use the fuel pump check circuit I hear fuel pump run and I hear a hissing noise from the fuel rail and regulator, and I assume that's just fluid moving through, even using the test circuit it will NOT fire unless I disconnect the fuel pump as if the system is flooding and doesn't crank until the ratio improves.