No power to fuel pump relay when key switch on?

I would make sure you have the battery to block ground and then the block to chassis ground strap, because the engine and transmission are seated in rubber you must have the proper grounds. Do you have the MAF plugged in? The PCM must see engine rotate and air movement before it will turn the fuel pump on. We should run the codes to see if any are stored as well.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Also check the IGN E fuse in the fuse panel under the hood, I have seen the fuel pump balance module go out on these trucks, here is the fuel pump wiring diagrams so you can see how the system works. Check out the images (below). Please let us know what happens.

the big 3 grounds are attached MAF is plugged in. when i bypass the relay, she runs good no check engine light etc. but also, RPM gauge does not move. Figured if the crank sensor was bad it wouldn't run at all. That is what is troubling the computer is not even sending a signal for the 2 sec prime. what all has to be satisfied for computer to do the 2 sec prime and of course send signal to engage relay.

The computer must see engine rotation which it sounds like it has part of that, the tach needs to work though, I would try unplugging the cluster. the tach might be shorted out. Also, I would unplug the MAF sensor so the comp will use the default value. If the MAF is not working, it will not show air flow when the engine is cranking so the computer will not turn the fuel pump on. Let me know.

Hooked up scanner computer shows 182 RPMs when cranking dash gauge still not moving but at least the ECM sees RPMs.

Also pin 30 on relay goes to fuel pump, right? If I ohm it, it goes to ground. the guy replaced the fuel pump, I wonder if it’s wired wrong at the tank.

Yes pin 30 goes to the pump which will ohm out to ground while still connected to the pump. While cranking does pin 30 have 12 volts, that is the test I would try.

No and I do not have power from the green/white PCM.

This would be power from the fuel pump balance module on the frame inside the left frame rail. (pink wire - while cranking).

What exactly would you like me to do?

I do not see a fuel pump balance module inside the frame rail near tank I see fuel filter.

Car Scanner ELM OBD2
Version: 1.114.11/1.114.11/iOS
DTC report
Connection profile: GMC OBD-II / EOBDDate: 1/26/2025 3:06:47 PM
============================
OBD-IIOBD-II
DTCs: 7
----------------------------
P0740 [0x0740]
Torque converter clutch (TCC) solenoid - circuit malfunction
Status: Confirmed
----------------------------
P0785 [0x0785]
Shift/timing solenoid - circuit malfunction
Status: Confirmed
----------------------------
P1860 [0x1860]
TCC PWM Solenoid Circuit Electrical/ Transmission Transfer Case Contact Plate "D" Short Circuit To Battery
TCC PWM Solenoid Circuit Electrical
Status: Confirmed
----------------------------
P1810 [0x1810]
TFP Valve Position Switch Circuit/ Transmission 4-Wheel Drive Low Indicator Short Circuit To Battery
TFP Valve Position Switch Circuit
Status: Pending
----------------------------
P1718 [0x1718]
TFT Sensor In Range Failure High
Incorrect Neutral Gear Ratio
Status: Pending
----------------------------
C2000 [0x6000]
Status: Pending
----------------------------
P0099 [0x0099]
Intake air temperature (IAT) sensor 2 - circuit intermittent/erratic
Status: Pending

Any of these keep the PCM from firing the fuel pump relay?

I don't think so. Terminal 30 at the fuel pump relay, while the engine is cranking do you have 12 volts?

No I do not have power at 30.

Does this truck have two tanks or just one? Sorry there is some confusion with the wiring if you have duel tanks. There is a fuel pump pressure switch behind the distributor I would bypass to see if you get power to the pump. Org to gry wires together. Check out the images (below). Please let us know what happens.

Only one tank just a 98 c1500 extended cab 2-wheel drive.

It does have the oil pressure switch did it change from 97 to 98 because I put the drivetrain from a 97 in this 98 if it is a different pressure switch, I can take the one out of the old motor.

I would just jump the connector to see if that is the problem.

I will try that this evening. thanks for your help.

Sorry for the confusion with the dual tanks, let me know.

Okay, if I jump the gray and orange wires the fuel pump comes on without the key on.

Okay, with the wires jumped does the engine start?

I’m sure it will I’ll have to check when I get home probably in an hour or so If it does run the bad oil switch?

Yes it does run with those jumped.

Okay, I replaced the oil pressure switch it now works but do not have the 2 sec prime from computer.

It will not prime every time, so can you drive the truck now? I would let the truck sit and then it should prime.