I am new to the diesel world, but not new to turning wrenches. I recently was given an 1986 F-250. She has 290k on the odometer and runs good at lower RPM's and on surface streets and I immediatly took her for an oil change since I didnt know how long ago it had been done. Mechanic said oil was clean and he emptied about 9.5quarts. Was pretty happy about that. But, When I took her up on the interstate, heading up a couple miles worth of 4-6% grade, she would bog down and eventurally die. Engine Temp was well within normal range. After a couple minutes of cranking, she would kick back over and we'd go again. Best description for feeling would be a vapor lock or an iced carb if this were in the gas world. I began troubleshooting a couple months ago with injector cleaners, fuel additives, then checked return lines and such for leaks as I was seeing air bubbles in the clear tube that ran from filter to fuel return rail, and replaced the fuel filter. Eventually the injector pump failed - verified by zero fuel output at several injectors. I replaced the Injector Pump - truck is now running with trace amounts of black smoke under heavy load - but it is STILL dying at wide open throttle for long durations. Vertical lift pump appears to be operating well as I get fuel sprayed across the engin compartment when I open the schrader valve down stream of the filter - but I dont have an actual fuel pressure tester. Transmission does eventually downshift - probably a little too late - but that seems to compound the problem as now the engine is at higher RPM.
Paul