To test the high pressure oil system, get the correct fitting for the ICP (injection control pressure) sensor hole, remove the sensor and pressurize the HPO (high pressure oil) system. The ICP is on the passenger side valve cover, near the alternator bracket, big sensor (and of course it is metric threads).
Then you have to get to the IPR (injection pressure regulator) and unplug the pigtail. Make your own pigtail and you want to apply 12 volts to one pin, and a ground to the other pin. When you command the IPR by applying voltage, do not do so for more than 60 seconds at a time, leaving 30 or so seconds between them. This allows the IPR to cool off.
The IPR is screwed into the side of the HPOP
Remove the oil fill cap and the dipstick, command the IPR and introduce the compressed air. Listen for obvious air leaks. By the way, another thing to be aware of is that when you release the IPR, it will dump the air into the crankcase and this is normal and not a HUGE leak.
If you hear a slight hiss coming form the HPOP (High pressure oil pump) area it is normal, however should you hear a loud hiss, this is not normal.
If you hear the hissing coming from the valve cover area, there are two likely culprits (and should be replaced as a set) and they are the dummy plugs and standpipes. Accessible by removing the valve covers.
If the noise is coming from under the HPOP cover, it is likely the STC fitting. The IPR would then have to come out of the HPOP, the HPOP cover comes off, remove the HPOP, remove STC fitting, install new fitting, reverse procedure and put it all back together.
The HPOP is located below and behind the turbo at the back of the engine. If you look back there you will see a hunk of aluminum that has a cast piece sticking out of it. The cast piece is the top of the HPOP, the sensor screwed into the side of the HPOP is the IPR.
It would be a whole lot easier if you got the turbo out of the way, and if you have to go in after the HPOP (or the fitting) you would have to remove the turbo anyway to gain access to the HPOP cover bolts.