Oil pressure low/warning

[Zachtaylor16]

Hello all I have a 2007 GMC Sierra new body style 5.3 with AFM (arghhh) and I was driving down the high way last night and I got a low oil pressure turn off engine warning an a P0521 code. So this morning I swapped the oil sensor and put in a new filter screen under the sensor knowing this is a common issue in these engines. That was no fix. The truck has about 215000 miles on it now and was wondering if I should try and chase on oil pump/other issues. I hear no noises and sounds like I have pressure but also worried that a bearing could be going out. I’ve had a cylinder 7 misfire code come up like 4 times over the last 2 years but it always goes away after about 5 minutes. It has a rough idle and I believe the cylinder 7 lifter is on its way out but no lifter tick. I was quoted from a new shop for a jasper reman engine but have heard the horror stories. I’ve just moved and don’t currently have a place to pull it apart and let it sit right now. Also when I had the issue I noticed that If I’d pull over and turn the truck off when I turned it back on it would go to about 30 psi then slowly drop. Normally I’d be over 40 psi at 65 mph. There are no leaks, oil is at the correct height and only has about 1000 miles on it. Any advice or experience would be awesome! Thanks in advance!!

[CamGTP]

Use a manual pressure gauge before you do anything else. Put the tester in the stock oil pressure port.

 

If that comes back with good news, you either got a bad new sensor or have a wiring problem.

[richard wysong]

where the pressure returns after a restart it sounds like the pick-up screen may be clogged. also there is a known problem with the o-ring seal on the pick-up tube that has been discussed at length here on the forum

[Zachtaylor16]

I don’t have a manual gauge available. My plan today is to add oil to submerge the oil pickup tube gasket and see what information I can get. Then I’ll pressure test Monday just to have more information before I do anything. 
 

[richard wysong]

I think thats a lot of oil and may cause foaming if the crank shaft is partially submerged

[Zachtaylor16]

It’s recommended by a lot of people and some YouTube videos on it. Seems like 2 quarts will get enough to submerge the gasket without getting it on the crank. You also put your vehicle at a angle to help focus the oil where the pickup tube meets the oil pump. It’s not a long term fix however just a test to see.

[Jworks]

I recently had the same issue.  Going to the lake at highway speed I was getting 21-22 psi at 60mph.  Coming home the check engine light came on.  Dealer said oil sensor code.  So I put oil sensor in.  Then the highway speed oil pressure went up to 30, no more; idle psi 21-22.  A member on this site said he'd had the same issue years ago, changed oil & filter and solved his issue.  I was really worried and was about 1000 miles from needing the dealer to change oil again.  So I took his advice and gave it a try.  I bought Mobil 1 and good quality synthetic oil filter and put it on myself.  Highway speed oil pressure is now 40.  Idle psi is sometimes 30 and sometimes 22..........which I do NOT understand.  Why would psi vary at idle speed?  Anyway, just changing the oil & filter got me back to 40 psi.  I don't get it; makes no sense to me but it worked for me.  My idle psi varying from 22 - 30 though I still don't understand.

[Zachtaylor16]

Yes I have changed the sensor but still have no pressure. For me though when I do a cold start I get about 40 psi and then as the oil warms up and thins out I get to about 25 and it just slowly falls now. I added an extra 2 quarts of oil and about 8 oz of seafoam. And had my truck on an angle. I had no luck with this. Next will be oil change and to manual test pressure. I can’t hear anything coming from the motor but worried I’m having blow by somewhere. Also the oil pump seems to be working because as I accelerate the oil pressure goes up. 

[richard wysong]

if the screens clogging  it will gradually lose pressure as it sucks up more debris and when you shut it off the crap drops back into the pan so it will have pressure again until it repeats itself. an oil change may help but the screen needs to be changed and the pan cleaned out

[richard wysong]

back in the 1980s GM had a trap door on the screens for the 3.8 v6 that would pop open when the screen clogged so the engine wouldn't be damaged but the result was the debris wiped out the oil pump then the bearings anyway

[Jworks]

richard wysong, by cleaning the screen I think you are referring to a oil pick up tube screen in the oil pan, right?  What you said makes sense.....if sludge falls off back into the oil at engine shut down the whole thing starts over again.  If thats the case, changing that screen and cleaning the oil pan makes sense.  I think I'll have this done at my next oil change.  It shouldn't be too expensive should it ?

 

 

Edited May 9, 2022 by Jworks

[Zachtaylor16]

Pulling the oil pan off on the trucks is kind of a pain. Have to take the transmission brace off and lower the front diff usually to get enough room. I’d say maybe 2 hours of shop time. 

[Jworks]

3 minutes ago, Zachtaylor16 said:

Pulling the oil pan off on the trucks is kind of a pain. Have to take the transmission brace off and lower the front diff usually to get enough room. I’d say maybe 2 hours of shop time. 

I would think sludge would drain out when you change oil & filter.....I don't know for sure though, I'm not a mechanic.  I'll check in to this at an independent shop vs the dealer.

[diyer2]

Zach and Jworks,

I would do engine flushes with a product of your choice before I started throwing parts at it or tearing it apart. If it has a lot of sludge one flush will not do it. 

Same thing if it's got varnish built up. 

Edited May 9, 2022 by diyer2

[Jworks]

diyer2, yes, you just may be right.  I just checked with my independent mechanic.  To pull the pan and clean the screen is $450.  Ugh.  He said GM says its ok at 6psi per thousand rpms......which I, and he, thinks is way way too low.  He said my psi was well within specs and wouldn't worry about it; but if I wanted to pursue it being that sometimes it idles at 21 and other times 30 he leaned toward replacing the oil pump.  What flush would you recommend?