Join Date: Sep 2008
Location: Oakbank, Manitoba
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HPOPs can slowly die or go out all at once. If the truck is stock, the HPOP can be on its way out and still run fine after it is started and drive normally. Same for a leaking seal, fitting or o-ring. They all typically work better cold, and usually gets worse as the oils thins during a second start. When running, the higher rpm and volume can easily mask a smaller leak that would prevent a start from being successful.
I am not clear on your "hard to crank" comment. Is this a it turns over slowly or it cranks for ever, but eventually started?
I would agree, don't go chasing parts. The FICM has absolutely nothing to do with low ICP, so what is different? The ICP for one thing. So, what is the IPR doing? I assumed it was good as you only reported low ICP. Of course, the IPR is only telling you what it thinks it is doing, not what it is actually doing. So you are back to checking for codes, and then back to diagnosing. If the IPR is at least 44% you should have 1500psi ICP and a start. If the ICP sensor was bad (telling the PCM to open the IPR due to a false high reading), you unplug it to give a PCM stored 1.2v (800PSI) signal to set the IPR closed enough to start.
If that doesn't work, then you suspect the IPR or the HPO system. This is why you check it with air. It is a simple an inexpensive test to find a leak (o-ring or fitting), bad IPR or associated wiring, or a bad pump. Who knows, it could be as simple as a wire or an o-ring.