No oil pressure, but also pegged out?

[Cwhite7089]

Yesterday I bought a 237k mile 2004 GMC Yukon, runs and drives like new, flowmaster muffler, stock everything else it seems and well maintained. Okay then, but today I noticed the oil pressure reads 80, but then on the gas drops to zero, only going back to 80 after stopping a while. Something like 20-30 seconds. After getting an oil change to be safe, as planned even before this, now it drops and climbs from one end to the other randomly while driving, mostly zero while on the throttle but not always, and every time it drops, I get the low oil pressure warning. But everything runs and sounds like new. Its stressful to say the least when it happens every 15 ish seconds. If I let it climb back to 80 after sitting, and then give it throttle like to leave a stoplight casually, the pressure will drop to about 60, climb back to 75 and drop to zero in a matter of a second or so, and again the warning and chime.
I'm clueless as to what exactly is the issue, its behaving very eradically and I cant seem to find answers elsewhere. Either it stays on 80 or on zero, but moved between both. I'm stumped and will appreciate any information yall can give me.

 

[PG01]

sending unit on engine and stepper motor for gauge in dash are the first things i would look at. both are known issues, especially at that age and mileage.

 

[Boatguy272]

+1 There is sending unit on the drivers side, back on the engine at the firewall. They are known to fail. Also, once you pull the sending until out. There is a screen/filter that you should pull out and either clean, replace, or just throw away. Next would be the stepper motor, or just find a rebuilt cluster. You can get one for a Denali, or Escalade and you will gain a trans temp guage.

 

[Cwhite7089]

+1 There is sending unit on the drivers side, back on the engine at the firewall. They are known to fail. Also, once you pull the sending until out. There is a screen/filter that you should pull out and either clean, replace, or just throw away. Next would be the stepper motor, or just find a rebuilt cluster. You can get one for a Denali, or Escalade and you will gain a trans temp guage.

Handy to know this last part. Thank you, as perhaps In the coming few years I intend to pull a trailer to camping trips

 

[Cwhite7089]

sending unit on engine and stepper motor for gauge in dash are the first things i would look at. both are known issues, especially at that age and mileage.

So I've seen, I just find it odd that mine behaves differently than all the others I see on YouTube or read about, theres more variation on mine if that makes sense. But that surely wouldnt mean an entirely different piece is the culprit I suppose so that's good news? Lol
Thank you very much for the input. I'm going to be replacing the sensor/sending unit over the weekend and see how that goes

 

[Fless]

Also, once you pull the sending until out. There is a screen/filter that you should pull out and either clean, replace, or just throw away.

There should be NO filter under the sending unit in this gen engine.

 

[Rocket Man]

Agreed with all the advice given in this thread. All very good and correct info.

 

[George B]

I would change the sender first. Maybe unplug it and run it to see if the gauge stays steady. I have changed the stepper motors in these. Pretty easy really. I have extra stepper motors if you need one. We can work out a deal.

 

[Cwhite7089]

I would change the sender first. Maybe unplug it and run it to see if the gauge stays steady. I have changed the stepper motors in these. Pretty easy really. I have extra stepper motors if you need one. We can work out a deal.

I appreciate this honestly and still of course hope it is just the sending unit, I should be finding out in less than a week

 

[Boatguy272]

There should be NO filter under the sending unit in this gen engine.

OK,,,, I had a 5.3 Buick Rainier back in the day of the same gen and it had one and in fact clogged so I assumed this had one as well.