Pressurized coolant after cold cranking

[azkcr]

Howdy guys,
Another 6.0 headgasket question.

Truck has dreaded Black Onyx gaskets and is knowingly sucking coolant.
WE KNOW THEY ARE BLOWN, THAT IS NOT THE QUESTION.

Truck was idling, died and then wouldn't start.
Next day, it started and ran. We turned it off and it wouldn't start back up.
Classic HPO system issue right? Wrong, pressures check out with the AutoE. FICM is fine. Batts hold 12v+.

It sat for the last 2 days, I cranked on it just now to do more diagnosing and after only a few minutes of cranking every few 20seconds it developed
enough pressure in the system to hiss out the cap at me.

So, that would confirm terribly blown HGs right? And would that keep it from starting?

No white smoke, no nothing. It just cranks away and builds up pressure in the coolant system. It is 50*F and the truck is
still cold, so why would it build PSI when cold and not start????

Thanks

[southend]

Look at your coolant, is it ok. Right off, it sounds like you have combustion gases entering the fuel rail to me.

Sent from my phone that somebody didn't help me get.

[twoicebergs]

Not getting fuel? What is the fuel pressure?

If the compression in all cylinders was low, the diesel would not burn; therefore, no start. How bad are the gaskets? You would expect a couple of cylinders to smoke if it is getting fuel.

Look at your coolant, is it ok. Right off, it sounds like you have combustion gases entering the fuel rail to me.

Injectors stuck open, or blown injector seals?

[azkcr]

Injectors are fine. In great shape.

My major question is if blown HGs would result in it not starting and a pressurized cooling system after only cranking for a few seconds...

[southend]

I'm just thinking, what if your injector is loose and your injector cup failed/cracked, or your head cracked in that area? Combustion gases in the fuel rail, no start. And combustion gases in the water jacket, degass bottle pressurized. Far fetched, idk. But if your convinced your "injectors are fine", then i'm out of ideas. Good luck. Keep us updated.

Sent from my phone that somebody didn't help me get.

[azkcr]

It's not far fetched, it's very likely to have those as issues

The reason I rule the injectors out is because it has <100k miles and I blame the HGs more is because they have been leaky for almost a year now.
Yes, it is one of those "if you knew it was not running right, why did you continue to drive it??" kind of deals.
Yes, I know what the domino effect is

It's a service truck that is used to work on/service a fleet of trucks and a lot of equipment.
So the 6.0 was not fortunate enough for down time

[azkcr]

Bump for some new info