Case 580 super m with intermittent no engine power. And fuel pressure issue. Has 8 psi at idle and 0 under WOT. If I pinch off the injector pump over flow line back to the tank it maintains pressure. Replaced lift pump still the same. Removed injector pump and sent to pump shop. It checked out good. Reinstalled still same issue. Any thoughts are very much appreciated.
Is there a hole in any of the piping or hoses? It could be a small crack in the injector pump connection. That happened to me on my tractor
No all fuel lines are good. I replaced the feed line to the lift pump, replaced all lines from lift pump to fuel Filter housing and to the injector pump.
I know the older 6bt cummins engines use a overflow valve to regulate fuel pressure. It is usually located on the injection pump where the return line connects. Sounds like it could be your issue. it is just a ball and spring inside a fitting.