Diagnosing erratic/high oil pressure...

[The Raven]

Working with my dealer and I think we are headed in the right direction here but before I spend a big chunk of money i'd like to engage some more experts. This problem is a little different than most that i've read about.

I've had a check engine light come on and then go off before I could get a reader on it three times throughout this past fall. Finally it came on and stayed on a few weeks ago and I simultaneously noticed that the oil pressure gauge was acting really weird. It would randomly spike to 70-80 psi and bounce around up there for a few seconds before dropping back down to 40ish where it normally hovers. With time it has gotten more frequent and sometimes just pegs at 80 for 20-30 seconds...I actually even had it drop to 0 for about 20 seconds one time. In reading of course I came across the bad pressure sensor problem and figured that must be it so I ordered a replacement sensor (OEM) and did the swap (that was fun as many of you know). Unfortunately that didn't fix the issue...just to be sure I went back in and removed that filter screen thingy too but that didn't help either.

So I took it to my dealer cause they have always treated me well and been very fair about prices. They spent three days with it and in that time they verified that the sensor is reading correctly, the oil pressure is indeed fluctuating just as the sensor indicates. They also changed the oil filter to verify that it's not a filter issue. It wasn't until the third day of messing with the thing that the tech caught onto one little detail that clued us in - the pressure always seemed to jump when slowing down or braking. He did a little further testing and found that he could make the pressure spike by braking hard or just getting the front of the truck way lower than the back (down a hill or whatever). So the natural conclusion seems to be the oil pump pressure relief, and based on my experience I tend to agree - I remember the first time I noticed the problem was while entering the roundabout closest to my house and that was the same spot that it happened again after I changed out the pressure sensor. You have to brake pretty hard coming into the roundabout from like 55mph and then do a pretty swift right-left turn motion going through.

What do you think - on the right track?

 

[OR VietVet]

Wonder what the mileage is on your rig? Could this be a sign of the oil pickup tube assembly o-ring failure? The hard braking and pressure climbing seems to be pretty close to the stories here where the pressure is low and fluctuating and it is recommended the problem vehicle be overfilled by two quarts and pointed downhill and pressure would climb, indicating the o-ring problem. Was this possibility brought up at the dealer? What type of oil do you use and filter brand?

 

[The Raven]

Wonder what the mileage is on your rig? Could this be a sign of the oil pickup tube assembly o-ring failure? The hard braking and pressure climbing seems to be pretty close to the stories here where the pressure is low and fluctuating and it is recommended the problem vehicle be overfilled by two quarts and pointed downhill and pressure would climb, indicating the o-ring problem. Was this possibility brought up at the dealer? What type of oil do you use and filter brand?

107k miles. Mobile 1 5w-30 and AC Delco pf48 filter religiously.

 

[OR VietVet]

107k miles. Mobile 1 5w-30 and AC Delco pf48 filter religiously.

Ok, was the o-ring brought up at the dealer?

More Information for GM GENUINE 12608835

Hope this fixes it though. But I cannot see how the hard braking and turning would make this the culprit. I have been wrong before though and hopefully the tech at the dealer is spot on.

 

[The Raven]

Ok, was the o-ring brought up at the dealer?

More Information for GM GENUINE 12608835

Hope this fixes it though. But I cannot see how the hard braking and turning would make this the culprit. I have been wrong before though and hopefully the tech at the dealer is spot on.

They didn't call out the o-ring individually, they said "there are several possibilities when it comes to the oil pump, but the pressure relief is the problem here". They also mentioned that there's a second pressure relief for the AFM system in there that they would also change out because it's cheap to do so, but they don't believe that one is the problem.

 

[Doubeleive]

interesting I have never heard of the oil pressure relief valve, I thought the pressure was controlled by the spring in the oil pump, hence different model pumps provide different oil pressure as needed/desired.

 

[Dustin Jackson]

Isn't the o-ring suspect when low oil pressure is the problem but I never heard of it being the cause of high oil pressure?

If they are opening the bottom and front of the motor might not be a bad idea to have them investigate a little and replace all suspected parts: oil pump, pick up o-ring, pick up tube maybe, oil relief valve

 

[Geotrash]

They didn't call out the o-ring individually, they said "there are several possibilities when it comes to the oil pump, but the pressure relief is the problem here". They also mentioned that there's a second pressure relief for the AFM system in there that they would also change out because it's cheap to do so, but they don't believe that one is the problem.

It makes sense to me that the oil pressure relief valve in the pan is a likely culprit here. It's a pop-off style valve that would cause this behavior if it's intermittently sticking closed. It's not common, but also no unheard of for these to fail in this way.

 

[donjetman]

interesting I have never heard of the oil pressure relief valve, I thought the pressure was controlled by the spring in the oil pump, hence different model pumps provide different oil pressure as needed/desired.

There's an AFM oil pressure relief valve in/on the oil pan:

 

[The Raven]

It makes sense to me that the oil pressure relief valve in the pan is a likely culprit here. It's a pop-off style valve that would cause this behavior if it's intermittently sticking closed. It's not common, but also no unheard of for these to fail in this way.

Does it only operate along with AFM or does it work on it's own? I had AFM tuned out a couple years ago so while all the components are still there, they aren't activating.