454 low fuel pressure

[Renncredible]

I have a 1999 7.4 vortec with both banks throwing lean codes. Bank 1 is just slightly above 10% sometimes but bank 2 is consistently 25%. Vacuum tested good @18. New fuel pump, filter, regulator and injectors. Fuel system harness was replaced in ‘21 and I’m still getting less pressure than I’d like. 52 psi with key on and holds perfectly when turned off. 45 psi at idle and doesnt go up much when throttled up. What am I missing here?

 

[Spareparts]

My bet is for FPR if the fuel pump is putting out the correct pressure.
If you pinch the return line what does the gauge jump to?

 

[Schurkey]

How old are the O2 sensors? Have you connected a scan tool to view their waveforms, or check the cross-counts? Have you verified ALL the other sensors?

Initial ignition timing, and electronic advance working properly?

EGR working properly? Knock sensor happy?

Decent manifold vacuum pressure does not mean there can't be small vacuum leaks into individual cylinders, screwing-up the air/fuel ratio.

 

[Renncredible]

My bet is for FPR if the fuel pump is putting out the correct pressure.
If you pinch the return line what does the gauge jump to?

I havent done that before Im not sure that my return line is rubber or anything that can be pinched. I just put in a new FPR last week

 

[Renncredible]

How old are the O2 sensors? Have you connected a scan tool to view their waveforms, or check the cross-counts? Have you verified ALL the other sensors?

Initial ignition timing, and electronic advance working properly?

EGR working properly? Knock sensor happy?

Decent manifold vacuum pressure does not mean there can't be small vacuum leaks into individual cylinders, screwing-up the air/fuel ratio.

The O2 sensors appear to be working properly. Brand new EGR as of a few months ago. New knock sensors are on the way not sure the current ones statuses. I have a super basic scan tool that shows an engine timing advance of 25 at idle, drops a few points when accelerating and dances between 27-33 when cruising.

 

[Spareparts]

You can pinch it off at the flexable line under the driver door.
I will still bet its your regulator. They all fit but most are the wrong pressure.
There are only 1 maybe 2 that have the correct pressure for a 454 even though they all fit that you find listed.

 

[Renncredible]

You can pinch it off at the flexable line under the driver door.
I will still bet its your regulator. They all fit but most are the wrong pressure.
There are only 1 maybe 2 that have the correct pressure for a 454 even though they all fit that you find listed.

When I pinch it off what should I be looking for?

 

[Schurkey]

Pinch slowly, don't let the pressure go up over 75 psi.

Point being, as you restrict the fuel return hose, the pressure should increase. If it doesn't, the pump can't provide higher pressure--it's weak, or it's not getting proper power/ground.

 

[Carlaisle]

You most likely have the wrong regulator. Multiple part numbers will physically interchange but they do not functionally interchange. The L29 requires a higher pressure. I have posted the correct part number before but don't have it memorized. Pinching the return line will tell you if the regulator is working but will not tell you if it is the correct regulator. Idle pressure should be 58-62 (or so). It's not super sensitive, but 45 is not acceptable.

 

[Schurkey]

Idle pressure should be 58-62 (or so). It's not super sensitive, but 45 is not acceptable.

I looked this up a few weeks ago in relation to another thread on this site. The way I remember it, 58+ was the pressure during priming--engine not running; perhaps needing multiple prime cycles to achieve full pressure.

RUNNING pressure is lower because the pressure regulator is vacuum-referenced. When the intake manifold pressure is reduced (has vacuum) the regulator reduces fuel pressure.

Engine running, pull the vacuum hose off of the regulator (if applicable and accessible) and plug the vacuum hose, the fuel pressure should increase. Same for snapping the throttle open--the sudden decrease in vacuum (increase in manifold pressure) should cause the fuel pressure to increase.

The '97 C/K service manual didn't provide an engine-running fuel pressure spec. They say it varies with altitude, etc. They only said it was lower than the priming pressure.