advice about oil pressure loss on auction vehicle?

[rogainegt]

Just picked up an 06 TB 4.2/AT/4wd with 190K at the auction (former fleet vehicle)... drove a few miles, and oil pressure drops to "0" (with associated valvetrain starvation noise).

Turn off, wait a few seconds, restart, and 40 psi.
Idled with 40 psi for 10 minutes.
Drive 30 feet, and pressure drops to 0 again... wash & repeat

Pressure now fluctuates 20-40 psi at idle - obviously a suction/delivery issue.

Not very familiar with the 4.2.
Is there a common issue with pick-up screen or oil return port blockage, or perhaps oil pumps/check springs? Or did I just buy a turd?

Of course it was "as-is" due to mileage, but showed no signs of oil pressure issues, just a cam sensor code.

 

[The_Roadie]

You probably bought a turd, but the I6 doesn't have a traditional oil pressure sensor. The gauge is basically lying because the oil pressure is detected by a simple on/off switch near the filter. The PCM makes up a number to send to the gauge that varies slightly with RPM and temperature, but you can't count on it for any diagnostic reason.

Measure the amount of oil that comes out when you change it, then see what happens. Was the level on the dipstick OK when you checked it BEFORE you bought it?

 

[limequat]

Yeah, check it with a real gauge and get back to us.

Was it the cam sensor or cam actuator? Actuator is powered by oil pressure, could be related.

 

[rogainegt]

Oil level was fine - a bit dirty.

I am assuming sludge in the pan impeding the pick-up & causing an occlusion.

I was curious if there was a more common reason for oil pressure loss

You probably bought a turd, but the I6 doesn't have a traditional oil pressure sensor. The gauge is basically lying because the oil pressure is detected by a simple on/off switch near the filter. The PCM makes up a number to send to the gauge that varies slightly with RPM and temperature, but you can't count on it for any diagnostic reason.

Measure the amount of oil that comes out when you change it, then see what happens. Was the level on the dipstick OK when you checked it BEFORE you bought it?

 

[limequat]

Oil level was fine - a bit dirty.

I am assuming sludge in the pan impeding the pick-up & causing an occlusion.

I was curious if there was a more common reason for oil pressure loss

Bonus points for using a word that I not only didn't know, but have never seen before. Are you a dentist?

It's common for the screen on the CPAS to become clogged. If that's clogged it's a reasonable guess that the pickup is clogged too.

 

[rogainegt]

"No, but I play one on t.v."

Tried it again earlier - no issues. Having it hauled to the shop, where flushing will ensue.

Bonus points for using a word that I not only didn't know, but have never seen before. Are you a dentist?

It's common for the screen on the CPAS to become clogged. If that's clogged it's a reasonable guess that the pickup is clogged too.

 

[mrphoenix80]

Odd we just pulled an 06 Envoy in today from the auction. Guess what??? It does the same thing except its a rod knock and not top end starvation noise. I will update when we get answers.

 

[rogainegt]

Bottom-end knock is never good... at least not with my luck.

I know Federal Mogul used to make rod bearings in a 0.001 (& some in a 0.002's) for popular engines.

When the 350's had an issue with cold-start knocking in very-low mileage engines some years back, I remember some shops were stacking split sets
(top .001's and bottom .002's - or the other way around) to alleviate the issue of G.M.'s poor machining ("Hache' en Mexico") - and it really worked.

0.002 is almost too small to measure sans digital calipers anyway

Of course mine is a 4x4... yay, fun pulling that oil pan.

No issues with it earlier, so... tomorrow: quick flush, drain, fill with kero (do not run) while engine is warm; drain & strain several times, inspecting strainer each time.
When confident, refill with cheap oil & ATF - run, repeat process.

Odd we just pulled an 06 Envoy in today from the auction. Guess what??? It does the same thing except its a rod knock and not top end starvation noise. I will update when we get answers.

 

[mrphoenix80]

If you pull the pan replace the oil pump pickup tube oring they have had failures in the past.

As for the one we have at the shop. I am not hopeful of a speedy recovery. But I am not working on it so I don't know what he is finding. Except that the LOF interval seems excessive just pulling the oil cap shows a ton of sludge. They ran engine flush through it and it was still knocking. Not that I thought it would help, it falls in the catagory of "I'm just doing what I was told to".

 

[jaguarjoe]

If you replace o-rings in an engine, don't use cheap Buna-N or nitrile rings like everybody sells. They don't withstand heat very well. If you want one time permanent o-rings that are only a few pennies more expensive get Viton O-rings. You can tell Viton by its color, it is not as dark as black Buna-N rings are.