[Stricko88]

Trying to sort out I get code P1211 under load. Dead headed the HPOP and got over 3000psi so I have ruled that out, also has a new IPR fitted. Next I removed the oil line from the RHS head and cranked. Truck would start when doing this test with hot oil, however when I retested the following day on a cold engine the truck would wind over and blow white smoke but wouldn't start. Same scenario on the LHS head. I reconnected the oil lines after each test and the truck would fire up straight away with minimal effort (both hot and cold) So I am suspecting that I have some worn poppet valves maybe? Any insight would be greatly appreciated

 

[RT]

Could be injector O-rings as well. Do you have a tuner? The P1211 is very common with every tuner that doesn't block the code. I don't think worn poppet valves could cause a P1211.

 

[Stricko88]

It had a tuner on which I removed to isolate that from being the problem. I can drive around under 60% throttle all day without fault and the ICP pressure is within specs (measured with a mechanical gauge and scan tool) But as soon as I go to WOT over a hill etc the ICP drops to 1900psi or less, the IPR goes to 65% power loss starts as well as black smoke from the exhaust and then throws the P1211. With a 3T trailer on the back it struggles to climb even a small gradient hill. Boost is spot on around 20psi, compression is lowish but even across all 8 cylinders (350psi) If i keep the engine off WOT it will maintain expected ICP pressure with the duty cycle where I would normally expect, however as soon as I open it up the pressure snaps off to under 2000psi and that's the end of it.
There was no oil in the fuel filter, and running the truck with no covers on did not point to any of the top o-rings leaking. My only thought with the poppets is that they are leaking low enough at 50% throttle that the pump can keep up, however when you go to WOT (especially once the oil is hot) The poppets cannot seal and are bypassing some oil back to the sump.