2004 GMC Yukon 4.8 oil pressure problem

[help please]

My Yukon has about 293000 miles on it. I've recently noticed the pressure sitting right over 40-45. It then dropped down to 0 and turned off. I Couldn't get it to start. Went ahead and changed o-ring in pickup tube and oil pump as well as water pump since I already had it off. Now at start it goes to 50 then drops once it's warmed up (about 10-15 minutes) to 15 psi. I put 10-40 oil hoping it would help but, nothing changed. What else could cause this to happen. 

[Jsdirt]

At that mileage, there's a good chance the engine is just worn out. Excessive big-end and crank bearing clearances will significantly lower oil pressure, as will excessive camshaft bearing clearances. Hotter oil by nature is reduced in viscosity, so that lowers it even further.

 

Naturally oil pressure will hit zero when the engine is turned off ... but if I understand you correctly, the pressure gauge went to zero, then the engine immediately SHUT ITSELF off afterward?

 

This could point to a loss of the 5v reference required for most engine sensors. The loss is usually the result of a chaffed wire shorting out on metal that rubbed through an unprotected or damaged section of wire, but can also be caused by a faulty PCM (engine / transmission computer), or bad powers / grounds to that computer, or an internally-shorted sensor. Without the 5v reference, none of the sensors that use this reference can report accurate information regarding engine operation, and will usually kill the engine, depending on which sensor is affected. If the 5v reference is gone, NONE of the sensors will work right. 

 

If the 5v reference is present during the stall, then you need to investigate the stalling problem before anything else.

 

If you find the problem to be solely a worn out engine, I'd buy some CHEAP dino 20w-50 engine oil, do an oil change with it, and just keep on truckin' until it quits completely.

 

Back in the days of the indestructible 350, I've run engines like this for hundreds of THOUSANDS of miles before they finally quit. Might not have had the most power they were designed to have, but they ran and got the job done. 

Edited April 9, 2024 by Jsdirt