94 XLT fuel pressure question; won't start

[Jcrews]

Tested fuel pressure today after priming with key on. Got 35 psi with a little bleed off. Started cranking and pressure drops to 0. The engine won't start, but is it normal for pressure to drop so low during engine start?

This was an intermittent issue before. I put injector cleaner in the tank and it helped for a couple weeks but now my problem has returned and become worse.

 

[MrShorty]

Tested fuel pressure today after priming with key on. Got 35 psi with a little bleed off. Started cranking and pressure drops to 0. The engine won't start, but is it normal for pressure to drop so low during engine start?

This was an intermittent issue before. I put injector cleaner in the tank and it helped for a couple weeks but now my problem has returned and become worse.

No, not normal. Fuel pressure should stay high while starting. Does the pump come on while cranking the engine (any time the engine is turning the pump should come on)?

 

[Jcrews]

Not sure if it comes in or not. I can't hear it due to the engine noise. How can I check that? I'm assuming no since there is no fuel pressure.

 

[Gadget X]

Swap out the relays for the fuel pump and the heater/blower under the hood, then try it again. If it starts then, you have a bad relay. Good luck with it!

 

[Jcrews]

Ok, I'll try it tonight. Thank you!

My only question: does the pump relay not tell the pump to prime? I think you see where I'm going. It primes, and I can hear it prime, so would that not confirm that the relay is in fact still functioning?

 

[Gadget X]

Typically, priming would mean that the relay is working. If it is "weak", then the relay might " kick out" when it is under more of a load. Just a possibility, and an easy check!

 

[Jcrews]

Typically, priming would mean that the relay is working. If it is "weak", then the relay might " kick out" when it is under more of a load. Just a possibility, and an easy check!

Got it

 

[Gadget X]

Did you ever figure out the problem?

 

[Jcrews]

Fuel pump relay was not the problem. Try the relay swap last night and no change. I did get it started but it idled very rough. Gonna try to pull codes again today.

 

[Gadget X]

Good luck with it!

 

[MrShorty]

I did get it started but it idled very rough. Gonna try to pull codes again today.

Did you have your fuel pressure gauge hooked up while is was running rough?

As for hearing the fuel pump, someone who stands near the fuel tank (maybe with a stethoscope or similar) can usually hear the fuel pump running.

For what it's worth, I had a fuel pump once that had significant trouble, especially hot. The pump would "run", but it would not generate enough pressure when hot. Left me stranded a few times. Diagnosis came from repeatedly testing the fuel pressure when it ran well and when it stalled/ran rough/wouldn't start.