7.4 vortec fuel issue

[Travon]

Hey guys! Having a low fuel pressure problem that I can't seem to solve.
koeo primes to 50psi then drops to 49psi. Upon start up it holds steady
at 45psi. Give it gas and it goes up to 50psi. Here's a list of what's been done.

New Delphi fuel pump changed when I first got it due to the same pressure.
Filter=Acdelco
Regulator
Upper and lower intake gaskets
Five-o Bosh 19lb injectors
Today checked all wiring to the pump. 11.7v at the pump, and ran ground wire from
the battery to the pump. Checked all other grounds with no success. Checked the power
to the relay and the pump power wire leaving out the fuse box.
So this is where I left off. Hopefully someone can see something I missed

Thanks in advance...

 

[RawbDidIt]

Says you've changed the pump and the regulator, but did you change the fuel filter? Also, did you clean the tank during the fuel pump switch? It's possible you clogged the pump inlet filter with old crap in the tank if you didn't clean the tank. Did you inspect the tank to make sure it's not gumming up your fuel system with rust/corrosion? Pressure is simply flow rate and flow restriction, if your regulator, pump, and injectors are operating correctly, the only other factors are the lines and the filters; you either have a filter that's restricting flow prior to the regulator, or you have a leak relieving pressure.

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[Travon]

Sorry left the cleaning of the tank out. Just assumed that's what most people
did when changing pumps. Tank was cleaned and a new acdelco filter was added

 

[RawbDidIt]

Sorry left the cleaning of the tank out. Just assumed that's what most people
did when changing pumps. Tank was cleaned and a new acdelco filter was added

Yeah, I try not to assume, no offense intended. Did you check for leaks? What does pressure do when you click key to on position prior to starting? Should still be some pressure with the pump after a couple minutes, lack of pressure after 2 minutes indicates a leak somewhere. Is it possible everything is working correctly, your gauge is just out of calibration?

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[Travon]

key on psi goes to 50 while the pump is on, then down to 49psi
after the prime. Pressure holds well at 49psi, I was also thinking maybe
my gauge is off so I checked it again with a different one. No change.
I did look at the lines from the tank forward, didn't seem to be any
leakage.

 

[RawbDidIt]

key on psi goes to 50 while the pump is on, then down to 49psi
after the prime. Pressure holds well at 49psi, I was also thinking maybe
my gauge is off so I checked it again with a different one. No change.
I did look at the lines from the tank forward, didn't seem to be any
leakage.

Key on, engine off, should be at 55-60 for a 454 if I remember correctly, 48-52ish with engine running. Only thing I can think of with all the new parts you mentioned would be maybe a vacuum leak? Correct me if I'm wrong, but the regulator depends on vacuum pressure, so it stands to reason that a vacuum leak would impact fuel pressure. I would think this would only have an effect while running, rather than with the engine off, can somebody corroborate this theory of mine?

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[Schurkey]

Today checked all wiring to the pump. 11.7v at the pump, and ran ground wire from
the battery to the pump. Checked all other grounds with no success. Checked the power
to the relay and the pump power wire leaving out the fuse box.

11.7 volts at the pump, with the pump running isn't bad...if the alternator isn't charging.

If the alternator is charging, system voltage should be over 14 volts. More than 2 volts of voltage drop on the positive side, plus some additional on the ground side...that pump is starving for voltage and current.

Perform a voltage drop test on both the positive side and the ground side of that pump. You must check the voltage as close to the running pump as practical.

Wouldn't hurt to check the current (amperage) draw, either.

 

[someotherguy]

11.7 volts at the pump, with the pump running isn't bad...if the alternator isn't charging.

If the alternator is charging, system voltage should be over 14 volts. More than 2 volts of voltage drop on the positive side, plus some additional on the ground side...that pump is starving for voltage and current.

Perform a voltage drop test on both the positive side and the ground side of that pump. You must check the voltage as close to the running pump as practical.

Wouldn't hurt to check the current (amperage) draw, either.

My #1 suspect if low voltage during running (with properly working alternator/good system voltage) would be the fuel pump relay and/or relay socket. Seen more than a few melted ones with cooked pins on the Vortec trucks.

Richard

 

[RawbDidIt]

My #1 suspect if low voltage during running (with properly working alternator/good system voltage) would be the fuel pump relay and/or relay socket. Seen more than a few melted ones with cooked pins on the Vortec trucks.

Richard

My understanding is that 11.7V at the pump is fairly standard for the small gauge wiring they put in at the factory, at least with the engine off. Is it running at 11.7V with the engine running?

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[Travon]

My #1 suspect if low voltage during running (with properly working alternator/good system voltage) would be the fuel pump relay and/or relay socket. Seen more than a few melted ones with cooked pins on the Vortec trucks.

Richard

Relay appears to be ok. Double checked it with the ac relay