Firrst off, I have a fair idea of WHAT may be causing this, because I've checked everythinng 6 ways to Sunday and the problem is very consistent.
Okay, so the truck was running fine when I first acquired it.
As time progressed it developed a surge at idle, then went to no-starting unless the throttle was depressed.
On a longer trip recently the truck just died when the accelerator was at idle, BUT FAILED TO RE-START.
After some hair pulling and tapping on the pump head, it fired up.
It has shut down and failed to re-fire numerous times since, even after I replaced the solenoid plunger and gave it more fuel via the fuel screw to get it to idle.
Last night, after having tinkered with the pump for 4-5 hours on Monday to get it to idle, it was dropping the idle out and stalling again.
The consistent part is that it WILL stall out if I let off the pedal and it will, 90% of the time, only re-fire after tapping on the pump head.
My fuel pressure to the pump is adequate, both cranking and running, no leaks in the supply lines, doesn't white smoke at any point, it just won't idle.
One other thing, this truck was being run on straight, filtered (supposedly), USED vegetable oil, but I have found signs of congealing in the OLD filter and the filler neck, as well as a light brown, waxy, substance coating the lines post-filter.
The fuel level sender also does not work at all, which I suspect is because of the WVO.
Is it possible to partially block the pump inlet and still have high-speed function of the injection pump, yet lose flow to cause stalling at lower rpms?
I'm also not ruling out a worn out injection pump, the truck has 230,000 miles SHOWING on a dead odometer and the pump appears to be the original.
So, any thoughts, anyone?
Mark.