Starving for fuel!
I have had several Ford diesels since 1985, and have driven and worked on them for 100's of thousands of miles. Beginning with the 6.9,, to the 7.3 IDI,, to the 7.3 IDI after market turbo,, and now 2 PSD's. I have researched, read about, studied, worked on, repaired and replaced about everything on them from front to rear - top to bottom,, at one time to another. I can usually figure it out. But,,, Now I am stumped!
One of my currents is a 95 PSD F450 5-spd. A couple of weeks ago,, the truck began dying on the highway and I would have to wait for 30 minutes or so before it would start. During the wait,, I periodically cranked and cranked and it would try to start, but it was like it was starving for fuel. After finally getting it to start,, I could drive 150 miles at highway speeds before it would die again for another wait. It did this 2 or 3 times. My first thought was it was the CPS,, but now it does not seem so. My experience with CPS's is that it just dies out of the blue,, and either starts right up,, or it takes a while during a cool down period. In that case,, while it is cooling down,, it will not even try to kick over(with no tach movement). Or,, if it has completely gone bad,, it never starts again
I first checked under both valve covers and harness connections,, inside and outside. All was well. All fuses were checked and all were good. I pulled the fuel filter cannister and regulator and completely cleaned all parts in both and replaced the filter with a new one. Due to signs of a brown muddy substance in the bottom of the cannister,, I pulled both tanks and completely cleaned and inspected them. The only fuel lines that were removed when doing so were the clamped hoses on top of the sending units.
Now things have gotten different and worse. I can get it started in my driveway,, but it will not stay running for very long. It runs normally for 5 minutes or so,,, and then it starts dying slowly like it is running out of (starving for) fuel,,, then dies completely. I put a gauge on the schrader valve port and it shows 50 psi,, and even when it begins to die the psi drops very little. Each time it dies,, it is very hard to get restarted, simply because it depletes the system of fuel when dying. Like you ran a tank out of fuel because of accidentally forgetting to change the selector to the other tank. We ran a scan with a high end Snap On scanner. There were no codes,, except the normal EBP code. All injectors buzzed out OK. We replaced the IDM with a known working one from another truck. Still acts the same. I unpluged the ICM sensor connector. Nothing changed. I inspected the IPR harness and connector. No signs of any problems there. I even swapped the accelerator pedal complete with the fly by wire switches from a known working one. I then replaced the fuel pump. The same problem still exists.
What we have discovered now,, is that the fuel system seems to build up air in it. Although,, I'm not sure if this is the cause of the problem,, or if it is just happening during the dying process from loss of fuel. After dying,, I can loosen one of the lines in the front of the regulator,, and it release air pressure. And if I do this a couple a times when trying to restart it,, it will start quicker than without doing it. Or,, I can even bleed one of those lines when the truck is running and starts to stumble to die,,, and it will stay running for another brief session before it starts to stumble again and die. This has stumped all that is in the know of PSD,s,, of the mechanics that I know.
Any suggestions on where to go now,,, before I set fire to it???
The truck is what I make my living with,, or as is now,, no living, no money. Any help would be greatly appreciated!