whitebullet3

Truck has died on me a couple times when its really hot, and this time it wont start back. I did the fuel pump jumper to see if I could hear the pump and the pump is not coming on and I have no pressure at the rail. Does this mean I should replace the pump or is there some other checks to do before I do so?

DeathCougar

iTrader: (23)

Define the "fuel pump jumper"?

milehigheric

Sounds like it...the Fp check bypasses the COR & VAFM/IGG1 triggers so the only other options are the pump or wiring downstream of the COR.

Confirm your Fp check (ignition was on wasnt it) and if you have the same results then get a new pump.

DeathCougar

iTrader: (23)

I just wasn't sure if he was bypassing everything and hooking right to the fuel pump? Or jumpering B+ and Fp

whitebullet3

sorry i jumped B+ and Fp with ignition on and pump was not on.

Hadmatt54

In a 91 when you jumper +B and Fp at the check connector and place the ignition in the run (on)position you are connecting the 12 vdc directly from 15 A ignition fuse, through the EFI main relay to the fuel pump. The circuit opening relay and the AFM are no longer in the circuit with this jumper in place.
Other things that you could check are the ignition fuse, the EFI fuse, the EFI main relay and the wiring (broken wire in the harness or a bad ground.) The first and easiest check are the two fuses. Why two fuses? The coil side of the EFI relay gets it's power from the 7.5 A ignition fuse. The contact side of the EFI relay is fed from the 15 A EFI fuse. If either of these fuses are blown your EFI will not function. If one of these are blown, you first have to solve that problem. It's always a good idea to check the fuse integrity with a ohmmeter. I've seen fuses that were blown, but the link inside looked to be intact. If the fuses are ok then the next check is to unplug the fuel pump harness from the body harness at the tank. With +B and Fp jumpered at the check connector turn the key to the run position. Take a dc voltmeter and measure the voltage between the blue wire (Fp) and the white/black wire (ground) at the body harness connector that you just unpluged. If you measure 12vdc between these wires then the circuit components mentioned above are ok and you turn your focus to the fuel pump.
The resistance of the fuel pump should be around 37 ohms. Connect the ohmmeter leads to the fuel pump wires going into the tank, if you don't read somewhere close to this (20-40), but read infinity or overload then your pump probably has a bad segment (an open) on the armature. Measure from each wire going to fuel pump to a chassis ground with your ohmmeter. If you get a reading and not infinity (analog) or overload (digital) then your pump (Motor) probably has a short.
If you didn't measure 12vdc at the body harness connector then you have to verify the circuit back to the source. First verify your ground circuit. With the voltmeter on ohms check between the white/black wire to a good chassis ground, your reading should be close to zero ohms. If this checks out then your problem is on the FP side. With an ohmmeter measure the resistance of the Blue (Fp) from the check connector to the harness connector at the tank, it should be zero ohms. If ok, remove the jumper and check for 12vdc from +B at the check connector to ground. If you get 12vdc here then the EFI relay and the wiring up to this connector are ok. If you don't measure 12vdc then you will have to do ohm checks on the wiring and test the EFI relay.
Get the picture...test the full circuit first, if not okay work your way back to the source testing components and wiring as you go.
Good Luck.