So, I got my fuel pressure gauge installed and working. At cold start pressure is 63psi. Once I start driving it is pretty much at 60 while cruising down the highway at 75. Depending on the steepness of an uphill grade it might drop to 57-58, and on slight downhills goes up to 61. I’ve read many times that the pressure should never go below 45psi at wide open throttle, and since my fuel pump is original with over 280k miles I decided to test it out. So...I mashed the throttle. Fuel pressure eventually dropped to 45 during the run after a few seconds...about 3-4 seconds in.

Is my pump on its way out? I installed the Ford blue spring kit when I got the truck 6 years ago. Does it need to be replaced periodically? Also, my truck is tuned with Innovative Diesel’s Extreme Street...excuse me, Xtreme Street, which I assume means even Xtra-er power...tune. I’m guessing this has an impact on pressure at wide open throttle?

Thanks!

 

I describe the setup as a constant volume pump, regulated pressure, and injectors fed by a bypass system. The fuel that the injectors use, more engine power, and more volume bleed off by the fuel the injectors use.

As volume through the pressure regulator is lowered, the pressure regulator reduces the return to tank bleed to compensate. The system is limited by the volume the HFCM can deliver. Volume delivery losses to the loop are from inlet piping restriction, primary filter restriction, and pump efficiency. Plus any loss in the plumbing to the secondary filter.

So, yeah, your pump might be getting tired at the brushes, or the rollers, vanes, or endplates are getting worn (most likely, the endplates take the worst). Any filter or pickup screen can also be a factor, and air seeping in at the o-ring connections at the top of the tank or the pump connection, although that's extremely rare.

Deficiencies of the regulator spring will reduce the regulated pressure (55-65psi) but will not cause the pressure drop below specs; that's a volume issue. But with a system designed for stock injectors without any overage (if the stock system had an overage of pumping volume, we would not see much lower pressure than we see at idle fuel pressure) will have compromises due to more injector demand.

A real wordy way of saying, if the pressure is lower than what you saw early on, I'd replace the HFCM, but it not be the main answer depending on what's going on at the tank. A 280k mile pump is ready for retirement, though.

But I'm tired as hell and none of that may make any sense.

 

Ha ha all makes perfect sense. I’ve been thinking my pump is probably on borrowed time anyway. I’ll add it to the list of things to do...someday. Hopefully soon!🤞

 

Racor fuel pump on the way!