deadhead test results, not sure what to think

Well, you don't have a pressure problem. When we dead head hpop, we had a high pressure hose made up with a manual gauge on one end and screw the other into the pump. We do not rely on electronics for this test, we want actual physical pressure. Even when we have this the pressure will drop immediately too once we stop. Once the ipr is de-energized, the oil is allowed to drop to sump, so don't let that fool you. It is common to see the ipr pig-tail connector get weak to the point it is ok to start the engine and low loads, but once the ecm is demanding higher duty cycle, it can't handle it and you get low icp pressure under high engine loading. Another issue is bad or weak 12 volt power at the ipr connector, which causes the same issue. I think you are ok with no hydraulic leaks since you did not hear anything with the shop air test and it starts ok when hot. I would look for an electrical problem with the ipr circuit at this point. The ipr ground is controlled by the ecm, so if the ecm ground is no good this is one of the first circuits to suffer. Check your ECM main power and ground circuits too from the batteries all the way to the ecm! Good luck!

 

I don't remember them holding pressure or a slow release.

 

Are you watching the ICP during a road test? 333 is when the ICP is below OR above desired, so is the pressure low or high?

 

I do not have access to SM here. Do you notice ecm battery voltage go down when engine load goes up? Is base oil pressure ok? Is the oil level full? Is the oil of good quality? If the oil is diluted or old, this will also cause lower pressure.

 

Hmmm. If you do a 5 minute recording of the engine running at idle and watch only ICP and ICP desired and the ICP line is very rough compared to desired then I would say one of the pumping plungers is probably bad in the high pressure pump. I have see this with the newer style, but not so much with the old ones. They will pass a dead head test because there isn't any flow, but can't provide enough flow during operation to keep up proper pressure to the engine.