cranks but won't start

91 C1500 5.0 manual wouldn't start one day, it will start if I use starting fluid and run for a second or two. replaced all the sensors one at a time still same problem. replaced throttle body with new, same problem. Replaced fuel pump, still same problem. Looked at schematic and see a hot fuel module in the circuit Could it possibly be causing my problem???

You need to check to see if you have power at the fuel pump connector. If not, troubleshoot backwards from there.

The "Hot Fuel Module" was only used on the Big-Block engines, so far as I know.

As said--verify that the fuel pump is ACTUALLY GETTING POWER AND GROUND. Assure that the fuel filter is not plugged. Make sure there's fuel in the tank--maybe you got siphoned overnight by some pack of roving dirtbags.

markj said:

91 C1500 5.0 manual wouldn't start one day, it will start if I use starting fluid and run for a second or two. replaced all the sensors one at a time still same problem. replaced throttle body with new, same problem. Replaced fuel pump, still same problem. Looked at schematic and see a hot fuel module in the circuit Could it possibly be causing my problem???

Click to expand...

Q: Does the fuel pump run for 2 seconds when you first turn the key from OFF to ON?
(No need to continue to the START position. You can actually better listen for/hear the
fuel pump operation without cranking.)

NOTE: You should also hear the fuel pump running for 2 additional seconds when you turn
the key from ON back to OFF. (Maybe not TBI systems?) If this isn't happening, you have
to do whatever it takes to make this behind-the-scenes behavior occur.

As well as following the guidance already shared above. (EDIT: I know that this is correct
for '96+ Vortec vehicles. Is this 2 seconds of fuel pump operation immediately after Key
OFF also the same on TBI engine bays?)

Let us know what you discover.

EDIT: I could only find the '2 seconds on' for the Key ON response in a TBI FSM.
(See attached.) If a TBI owner could chime in on what happens to the fuel pump
when you Key OFF I'd sincerely appreciate it. (Note: Since the TBI setup doesn't
hold onto the fuel pressure after shutdown I'd assume that the pump isn't run
during the shutoff sequence.)

Erik the Awful said:

You need to check to see if you have power at the fuel pump connector. If not, troubleshoot backwards from there.

Click to expand...

Yes there’s power at the pump and it primes when the key is in the on position

Erik the Awful said:

You need to check to see if you have power at the fuel pump connector. If not, troubleshoot backwards from there.

Click to expand...

There’s power at the pump

Check the throttle body and make sure you're getting fuel spray. You should see a nice cone of fuel in each bore. If either side isn't spraying it'll be a pain to start.

If either or both sides aren't spraying, check to see if the red wire is hot with the key on. It should be hot all the time - the computer switches the ground on and off for your injector pulse width.

If the red wire has constant power, it's likely a pigtail issue. The injector connectors and pigtails are notorious for failing with age. Fortunately they're cheap and easy to fix.