2003 Yukon 6.0 losing oil pressure

[Robb Burkee III]

Good afternoon everyone! I have a 2003 yukon Denali with a troublesome 6.0L and I need some ideas. I rebuild the engine after I blew a head gasket and noticed some scoring on the cylinder walls. (The engine was slowly losing oil pressure before the rebuild). With the new rebuilt engine in I am only starting with 35psi of oil pressure and it continues to drop as the engine warms up. By the time the engine is at operating temp it is down to 5psi. Is it possible an O-ring is bad? I just wanted some ideas before I start tearing into it again.

[Jsdirt]

That o-ring in the pump pickup tube would be my first guess ... but are you going by the instrument cluster gauge, or do you have a hand-held gauge plumbed into the engine block port? The cluster gauge is notoriously unreliable, so I'd back those readings up with a hand-held gauge before tearing into anything.

 

I don't think there were many AFM engines in '03, but, if by some chance that was an AFM engine, there's quite a few places you could be losing pressure from. RPO codes L76, L77, LFA, & LZ1 are 6.0 AFM engines.

[BlancoSilverado]

I am not sure if you have a screen at the pressure sensor but if you do i would take it apart and see if its gummed up.