Help again. This story probably starts back in this thread https://www.ford-trucks.com/forums/1...-pressure.html

At that time I replaced the fuel pump while diagnosing the issue. On January 3rd the pump died. So about 6 months after installing it. I kept the one I removed since it was apparently still good and change out the new one with the old one in a parking lot. All was good for about a week and a few hundred miles. Then the fuel pressure became erratic, it would bounce between 40 and 70 PSI. At this point I do not have time to look at it or fuss with it so I take it to a mechanic. He changes the filters and says its fine. I convince him to drive it to make sure. Everything was fine until one day he was driving it and 0 pressure. The old pump apparently died. The assumption was the old pump was on its way out. In goes a whole new pump/housing assembly. After numerous test drives it is determined to be fine. I pick it up drive 30 miles home and everything is good. The next day I start it up and the fuel pressure is again fluctuating between 50-75 psi this time. I am use to the pressure bouncing around while running a few psi and Key on Engine off holding steady. Now with the key on engine off the pressure fluctuates about 5 psi and with the engine idling it is fluctuating up to 30 psi.

Tonight I am going to put a manual gauge on it and probably check the regulator spring/seal if the manual gauge is erratic as well. Anything else I should try or look at?

 

At that time, you said it was the connection at the hose to HFCM. Did you ever do the alternative tank check, or drop the tank to see if the foot is coming apart.

Another thing that can cause the fuel pressure to rapidly vary is if an injector copper seal is degraded. That's check if you see air bubbles coming up through the fuel in the secondary filter when cranking by jumping the starter connection from the pass fender. But considering the history, I'd be looking at the tank.





>>>Thank you sir. Your video is what i an following. After reading that forum post you expect me not to go straight to dropping the tank..... lol.

I wiggled the feed quick connector while pump was running and i could change the flow rate so i assume i have a leak there. Going to replace those. Just picking up more hose clamps. And fuel line. If course all i have in my shop is 3/8 and 1/4.

>>>So far replacing the quick connects seems to have fixed my flow issue.

>>>But saying IT was the only problem can only be addressed with miles. Eric though he had his problem solved, before he didn't. I'd do an hour or two of driving one evening.

 

I never did any more diagnostics after replacing the input lines to the HFCM. Not going to get much done tonight. Feeling under the weather. I went out tonight and checked and it was holding steady with the key on but was bouncing around idling. Drove it down the block and back and as the rpms increased the pressure would level out more and once cruising around it was pretty consistent at 65psi. Then it goes back to bouncing around at idle.​​​​​​​

 

Trust me, time to drop tank .clear out lines, clean old foot out of tank. Install new foot and problem will be solved.
If you really want to know if the lines are clogged, you can do the 5 gallon test.
. P.s. I had same problem and wanted to do anything I could to not to have to drop tank. But our trucks are old and them foots go bad in deisel after 18 years.