1995 F250HD with 7.5l motor.
changed THREE fuel pumps now, and still have a hot bogging problem. here are the specs

FUEL PRESSURE COLD is 30psi, and steady, pull vac line off of regulator, and pressure pops to 45 PSI
FUEL PRESSURE HOT sits at 30 psi, and drops to 20psi or lower upon opening throttle. Pull vac line off of regulator, and pressure jumps to 42 psi, but still drops to 20 psi or less when revving engine.

so, since I have replaced ALL the fuel pumps (one of them 2x....) is it probable, or even possible that the fuel pressure regulator is SHOT, and bypassing more fuel when it gets hot? I do not know the history on the pressure regulator, but fuel flow is good on both pumps, both tanks are full, fuel filter is new. and there are no fuel leaks. Fuel DOES NOT leak down when shutting off the engine, so that should rule out a bad injector.

Im running out of ideas about as fast as this thing is running out of fuel....

 

A fuel pressure regulator is cheap enough to replace. Your issue is not their common failure mode but worth a shot.

 

Agreed on not the common failure mode. thats why I was asking here. What else can cause a low fuel pressure situation such as this? Am I just that unlucky and have THREE crap fuel pumps? is it time for me to rip out all the fuel lines and replace with a high volume/high flow aftermarket. Should I just stick a lit road flare in the filler neck and be done with it?

Motorcraft seems to have discontinued the pumps for this truck, so aftermarket is the only game in town. Are some brands better than others, or should I just fasten the bed with zippers and get used to changing these damn things all the time?

 

Did you replace the entire fuel delivery module(s) or just the pump?

 

the entirety of the plastic module, kept the hangars and the level senders in both tanks

changed FPR, and we have a "change"... fuel pressure now sits at about 25psi on both tanks at idle, goes to about 30-32 when vac line disconnected. Rev it up, and the pressure needle goes bananas, but steadies out in a few seconds. Havent driven it on the road yet, but let it run til good and warm in the yard. No problems revving in the yard until I thought its insides would become its outsides.

frankly a bit concerned about the vibrating needle (about a 10psi sweep, but who knows what it actually is) and can feel a "knocking" in the gauge like a pressure surge at all rpms. Almost feeling like I should remove and cap the FPR vacuum line and just manually increase the pressure that way. let the spring do all the work without the vacuum assist

change tanks, and the truck doesnt even notice. No change in fuel pressure at all.

 

Ok, let me clarify some things. I misspoke yesterday about having changed the front pump 2x. I HAD the second pump on hand, and changed it this morning. I autopsied the "old" pump when I got it out. Keep in mind this pump was put in 2 weeks and less than 150 miles ago.

Housing top was broken around the return line seal area. Was this causing some of the problem, I dont know, but its plausible.
Red rust EVERYWHERE in the socks. This was probably the cause of the low flow/pressure issue that I was getting. I knew there was some in the tank, but it didnt appear to be THIS much.
Pump itself looks OK (I had good pressure when it was getting fuel).


internal sock badly filled with red rust. Still seems to pass air OK, but that doesnt really mean squat

Bottom of housing has some sediment in it.

pump outlet looks good

external sock has some signs of red rust, but not too bad.

housing top is badly cracked around where the return line enters. This may be the root cause of the issues, along with the rust


I will say that this pump was an SOB to install on the hanger. the piece that locks onto the hangar hung up like it was too small, and I had to use a LOT of force to get it to seat. I dont know if this unseated any pieces internally, but again, its plausible. (so that makes it MY FAULT). I figured the cracked housing top would be OK, but this deformed at some point after I installed the module in the tank.


Now, onto the situation update. I have a steady 32psi on front and rear tanks at idle. when the vacuum line is removed I get about 38 psi on both tanks. I am not currently losing pressure when revving the engine, but I wasnt losing cold pressue anyways before. I need to get it out and run it to see what it does hot. This time however I am hopeful that the issues are "solved" or at least start to present different.

Looking at the fuel system in this truck its simple (yet complicated). You get pressure from each tank, and the check valve in the other tank maintains it. So, if I had a bad module in the front tank, it could potentially cause issues on both tanks. there is no separate selector valve in this truck.

Right now I need a shower and a change of clothes. Im getting a little tired of using the expensive cologne (87 octane). It does drive the wife nuts, but not in the way you would want it to.....

 

ok, we have a result......

Took the truck out for a bit of a drive, mostly on the rear tank as its currently full, Used the front for testing mostly. When the rear starts acting up, flipping to the front tank is just like flipping a switch. Truck comes right back to life and runs right. Too bad that tank only has a little over 5 gallons in it. Rear had a good amount of dust and sediment in it that I couldnt get out, so it looks like that pump sock is going to be plugged as well. Not terribly happy about it, but it is what it is. At least I know where the failure is.


Rock Auto has the pumps for cheap, just a hair over 21 bucks each, so Im gonna get a pair for the back, and another for the front to have on the shelf if/when the socks plug up again

on another note, does anyone have a GOOD way of getting the interior of the tanks cleaned of sediment and rust. I dont have a shop around that can steam them out, and dont really want to pop for 80 bucks a piece for new tanks.