Oil pressure issue

[Idriveaho]

2008 Hoe 5.3 flex fuel

Background of issue at hand. Over a month ago it was time to change oil. After changing I found metal flakes coming out of the filter. I had changed to the super tech 5w30 full synthetic high mileage and used the ac delco filter. Normally I was using pennzoil with the same filter but they didn’t have any in stock. After changing I noticed pressure being lower than normal. 2 weeks ago it got so low after being warmed up at idle the light chimes on to stop engine. No noises, engine runs smooth. I decided to change the oil pressure sensor and nothing changed. Used oem part for that.

After the sensor change the pressure was getting worse to where at stops I would have to give it a little gas to keep pressure up from chiming. While cruising at highway speeds it gets 30 psi on up. I decided to park it during my work week and take the back up vehicle while getting parts ready for oil pump and pickup tube. 2 weekends later and wishing I would of rented the correct tools ahead of time (balancer puller and installer, better impact….) I got the pump changed out. Went with the melling high volume that came with the pickup tube. Also last minute since I had the pan off, change the pressure relief valve in it. Ordered melling for that and they just repacked a gm original in it. Used ac delco filter again but this time had pennzoil high mileage full synthetic and upped to 10w30. Fired it up and still had lower pressure than it should. This time it was higher than before.

Today while driving to work hitting 35 to 40 psi on the interstate. Cold pressure at start was 20. But as soon as I get off the exit and at a stop the chime went off again and it’s back to like I didn’t just do all this work to it. I borrowed a scanner and couldn’t find the option to look at live data for oil pressure. Guy I work with had his scanner with him, he tried and same deal. Luckily when I replaced the sensor I left the back sound deadner on the intake off so I could access better. I will get a t fitting and get a pressure gauge and see if it’s truly low or not.

I’m thinking maybe trying a different oil filter. Maybe the motor in the gauge is bad. Forgot to mention I took the old pump apart and there was some light scoring in it.

 

[strutaeng]

Umm. Well, if you found metal flakes, that's never a good sign. You already replaced the pump, and you still have low oil pressure. Pretty sure your bearings are gone (they are the ones that actually dictate oil pressure.)

I would say time for a rebuild...

You can try removing the pan and removing a few rod or main bearings for inspection. If those look fine, probably cam bearings. But if bearing material ran through the oil, I would do a complete teardown and overhaul. Or get a remanufactured shortblock or longlong depending on your budget and mechanical capabilities.

Edit: I just realized you mentioned your old oil pump was scored... basically, what I just said...

 

[lspann3525]

Also did you change the lifter valley oil filter underneath the oil pressure sensor if it gets dirty or clogged it will cause low oil pressure readings

 

[Idriveaho]

Also did you change the lifter valley oil filter underneath the oil pressure sensor if it gets dirty or clogged it will cause low oil pressure readings

It never had one in it so I left the new one I bought out of it.

 

[OR VietVet]

Your live data scanner will not give pressure. It gives voltages that relate ro a pressure amount. I believe @Fless has the voltage chart. Maybe this is it.

 

[donjetman]

@Idriveaho
you stated at cold startup your oil pressure is 20 psi. IMO that's is a dead giveaway you have a serious leak/problem.
My stock 200k mile engine has 50 psi at cold startup even when I run 0w-20 oil.

 

[Fless]

Your live data scanner will not give pressure. It gives voltages that relate ro a pressure amount. I believe @Fless has the voltage chart. Maybe this is it.

View attachment 455008

A 2008 (NNBS) will have a PID for oil pressure.

 

[Idriveaho]

A 2008 (NNBS) will have a PID for oil pressure.

Another guy I work with had a Bluetooth scanner that does the 2 way communication. Looked it up with his app and it showed it. What the gauge is reading is the same as the sensor. I’m going to get a mechanical gauge hooked up to make sure.

 

[SpareParts]

Any gauge will read the same pressure as the only reading anything can take electronically is from the oil pressure sensor.

 

[2006Tahoe2WD]

Pickup tube O-ring?

 

[Geotrash]

It never had one in it so I left the new one I bought out of it.

It should have had one unless someone else removed it. They are hard to find down in that hole sometimes. I had a blocked screen in my 2012 when I bought it and a new screen + sender solved the problem in my case.

 

[DSRBLDR47]

In all of your (or anyone elses) low oil pressure situations, do you also lose power? I'm going through a power loss condition when my oil pressure drops. i had a shop put a mechanical gauge on the vehicle and while driving, the power loss happened the same time the pressure dropped.

 

[2006Tahoe2WD]

In all of your (or anyone elses) low oil pressure situations, do you also lose power? I'm going through a power loss condition when my oil pressure drops. i had a shop put a mechanical gauge on the vehicle and while driving, the power loss happened the same time the pressure dropped.

Interesting, I haven't heard of that. I'm thinking if the low pressure causes increased friction somewhere and apparent power loss that seems pretty drastic. By drastic I mean e.g. bearing failure. Doesn't seem like you would have bearing failure over a long period of time.

 

[rdezs]

Have you pulled the valley cover/VLOM and addressed that leaking internally? It's right up there on the most common causes of low oil pressure besides the pickup tube o ring..... And it's pretty common to find the bolts holding it down finger tight or less.

 

[rdezs]

Also, as low as your oil pressure is, I'm wondering if it's affecting your variable valve timing which in effect you're feeling in the way of a power loss.

 

[DSRBLDR47]

I just got this vehicle and I don't even know what the vlom is! When I originally got it it had a metallic ticking sound which we thought was a plugged catalyst. I got a y pipe from a denali complete with original cats and installed that (after discovering the output flange was bigger!) with no change. Finally took it to a shop that diagnosed the ticking sound as a weak return spring on the starter clutch. And of course the power loss is still there, the cat wasn't the problem. I have a hard time believing the oil pressure drop is causing the inadverent triggering of the DOD. I'll do some digging on the vlom. If you have any info you can point me to that would be great, thanks!

 

[2006Tahoe2WD]

Something to try...
On an iphone app or scanner watch the long term and short term fuel trims using graphs and see if there is a change when the power drops. I've done this on my iphone while driving. You might be able to tell if the ECU is telling the injectors to reduce the fuel.

 

[DSRBLDR47]

Do you have a recommendation on a scanner to get?

 

[rdezs]

The VLOM is a common source of low oil pressure. As mentioned, it's common to find the bolts loose. Low oil pressure will affect your variable valve timing, and hence your power output. The whale pick up tube is probably number one on the list for low oil pressure. Other items are the oil pressure relief valve getting weak in the oil pan, and the oil pressure relief valve built into the oil pump getting old and weak as well.

I would do some reading here on the forum and get familiar with your engine and the AFM system.... And don't throw money at shops that don't have a clue what they're doing.
It's preferable if you're up to turning a few wrenches.... You'll find instructions for everything you need to know right on this forum, and it will save you literally thousands of dollars in Shop prices.

 

[rdezs]

One thing to remember is take the time to make sure things are diagnosed properly before throwing parts at it. The metallic ticking you describe, is often nothing more than an exhausting between the exhaust manifold in the cylinder head. They can sound just like a lifter ticking. Look for a missing or broken exhaust manifold bolt as well.