2001 dodge 2500 cummins diesel. Always started immediately , now when engine cold, first start has trouble starting and only will start if giving it some throttle. This is independent of outside temp. If just turned key on engine off fuel pressure bleeds down rapidly to maybe 5psi or less. However if bump starter fuel pump stays on and is supplying 18 psi fuel pressure so I ruled out fuel supply problem, seems like it wouldn't be vp44 or injectors? Thought maybe grid heater but keep- reading about people deleting grid heater and it starts even in cold temps. once started, even before reaching operating temp it will restart no problem again independent of outside temp. Air filter was partially clogged but after removing there was no change.
Any ideas would be greatly appreciated
Any ideas would be greatly appreciated