Another HPOP Problem but weird....
 

I am a technician for Caterpillar and I am pretty familiar with the HUEI style engines but this one is throwing me for a loop. I pull in my driveway with 2005 E350 6.0 and went back out and the infamous no start. After checking the oil pressure on the test port at the back of the engine I am only getting about 350 psi while cranking. I then decide to do the "Air" test at the same port. I had a tank of compressed Nitrogen and just hooked up the test fitting I had installed straight to it and used a regulator to see if it would leak. Here is the kicker.... The HPO system will hold just under 200psi of Nitrogen with no leaks what so ever (even with supply pressure tank valve closed). When I get over 200psi the IACV will start to bypass through the weep hole on the back of the engine. At first I thought the valve was bad. I had a running donor van that I swapped the valves and still nothing. The other van started with my valve in it so I left it. But both valves will bypass at around 200 and over. Knowing how Cat does their valves I figured that was the max amount on the spring inside the valve and the valve actually bleeds some of the oil while running to the spring side of the valve to help with spring pressure. (To keep from having a 500psi monster spring in the valve). I guess I have pretty much come to the conclusion that the pump is bad but want confirmation from someone who knows more about these than me. The injector tubes are not leaking and I am pretty sure they were updated when the van belonged to the company my friend works for. The STC fitting has also been updated. Suggestions would be greatly appreciated.

Thanks,
Derek

you have to apply 12volts to the IPR valve to do a air test right, you have to make up a pigtail with an old connector or get one of those facy tools to hook up to it. Were the dummy plugs replaced?? could be a blown oring on one of them causing this too, very common. try it once it is cold and see if it starts, if it does them probably a dummy plug if the STC fitting was already replaced.

Pigtail from a C7 Cat engine injector is the same but yeah I've done all that already. Dummy plugs have been replaced if not it would leak under 200 psi.... That's the thing any kind of leak would have shown up at 120psi since that's what everyone uses....

Did you check ficm volts?