I think my fuel pump is on its way out but I’d like other opinions. It's the stock pump with 133k miles and ~8 years.

I’ve got an AFPR with a gauge under the hood. With the vacuum line off, I’ve got the fuel pressure set to 43.5psi. With the vacuum line on, at idle, fuel pressure is in the 35psi area IIRC. Problem is, if I rev the engine (no load) and watch the gauge, the pressure drops initially and comes back a little bit but overall it has still dropped. I.e. pressure is not increasing with increased rpm (less vacuum). Does this no load scenario mean anything or do I need to test it under load?

Additional info:
Fuel filter is brand new AC delco
Ford SVO injectors w/ PCM tweaks for them
No fuel in AFPR vacuum line
AFPR will hold a vacuum with my vacuum pump so it’s not leaking
Fuel pressure will slowly bleed off once the car is shut off (over a period of hours)

Thanks,
Rob
95Z28

 

Revving your engine under no load isn't necessarily going to show you anything. When you aren't under load, the vacuum can actually increase at higher rpm. The only way to measure the effectiveness of the pump is under load, where the throttle opens, and the vacuum disappears as the engine slowly starts to increase rpm.

 

Thanks for the info! I'll check things out under load and see if I still have questions.

Rob