Odd high pressure oil problem - need suggestions

[Jaybee]

Ok, this truck belongs to the company I work for. It's got about 320,000 on the clock now, and this week developed a new problem. For the last 20k miles it's had somewhat low high pressure oil readings (all numbers in post from an NGS) of about 550psi at idle along with a rough idle with IPR at around 11 or 12%. Oh, and 20k miles ago it got a new IPR, a new ICP sensor, and all the injectors rebuilt (by Bean) with new orings which didn't make a bit of difference as far as the pressure readings. (the injectors drastically improvemed cold starts, though!) Lately the truck has suffered from the oil reservoir bleeding down if it sits overnight or longer requiring a prime on cold starts - once warm it restarted fine every time.

This week it completely quit restarting when warm, and the reservoir is still full of oil. With the NGS I can watch the ICP as I try to start it and I'm only getting a max of 132psi - nowhere near enough to fire the injectors. With the ICP sensor unplugged to trick the computer into thinking there's enough pressure to fire the injectors it still won't start. The running pressures and IPR look ok when hot just prior to shutting it off - but nothing on restart. On a cold start the pressure rises very very slowly to about 450 psi at which point it fires up and idles at 550 - 600 max.

So, what could cause to a big pressure loss once warmed up? What other tests do you recommend?

Thank you,
Jason

So, what coul

 

[Double-S-Diesel]

whats the IPR when cranking?

 

[Jaybee]

Seems like it was around 20% - but honestly was watching pressure more than anything. I can do the test again next week and watch IPR.

 

[Mike]

The loss of HPO after the engine is warmed is puzzling, when was the last oil change done, what grade of oil was used and did someone use an additive they shouldnt have? I'm leaning towards a foaming issue here but I could be all wet.

I know you got new injectors and o-rings but humor us and pull the fuel filter and check the color. I've seen more than one new oring get nicked on install only to let go X0,000 miles later.

 

[Mastertech]

Quantity and quality of the oil is a good place to start.