Today I replaced my fuel filter on my 98 4.6 F150 and before I took the old filter off I read the fuel pressure with my OTC fuel pressure gauge. Just wanted see if it would show a difference. Reading before new filter at idle 30.5 psi and engine off 39 psi. Reading after new filter at idle 31.5 psi and engine off 29psi. I don't understand the 10 psi difference at engine off. Could someone explain?

 

did you only do it once?

 

No I checked it 3 times before and maybe 4 times after to make sure. That is why I stated that I have a OTC fuel gauge and not a AZone brand.

 

The regulator is not consistant.
The pressure the pump applies even accounting for the filter drop is much more than the regulated pressure.
Be sure to run the engine before taking readings. If not, air is present in the system until it bleeds out when the injectors operate.