You already did. You can't have strong compression with broken or worn piston rings.

Plus, you'd see a crap-ton of exhaust smoke with worn or broken piston rings!


Also, how quickly does your oil pressure dash light turn off during engine cranking/startup?

 

A compression test only tests the compression rings? Pretty sure you can still get great compression and have the oil control rings not doing their job, and thus burning oil.

On a cold start, oil psi shoots immediately to 50. hot idle around 12-16. Hot w/ throttle is 50

 

Sounds like great oil pressure. I was under the impression that a compression test measured the total seal of the combustion chamber, so great compression readings would rule out leaks from anywhere.

Could you have great compression and still have one failed component leaking?!

I was thinking that your compression test ruled that out.

The compression test establishes the engine’s ability to pump air and build cylinder pressure in the bore. It checks the sealing of the cylinder under pressure and the piston rings’ ability to keep the compression gases working against the piston crown instead of escaping into the oil pan. It also is an indicator of the ability of the valve to seal against the seat and make an airtight bore.

You have strong compression numbers, so your piston rings and valves are sealing.

 

Based on googling around, it seems like failed oil control rings could actually give you higher compression readings. The job of the oil rings is to scrape away oil, not to provide compression. If they fail to do their job, the leftover oil could actually contribute to higher compression (effectively a wet compression test, sealing the compression rings better) and be burned off.

I think the leak down test might help pinpoint this, as it tests the cylinder @ TDC and does not turn the engine over, so there shouldn't be any oil on the walls to contribute to higher readings. My theory anyway

 

You could do a leakdown test if you still think that there is some compression leakage. The important thing about a leakdown test is that all cylinder leakage does not occur past the rings.

If the leak value is high, you need to listen for where the air is going. If the air is entering the oil pan (by listening through the dipstick hole), then the rings or cylinder wall is the problem.

Air escaping from the throttle body is an intake valve.

If the noise is heard at the tailpipe, it is an exhaust valve.

This is why the leakdown test is a complement to the compression test. It determines the actual location of any leakage.

 

There are 3 grooves in each D2 piston, but 5 piston rings in those grooves.

The top 2 grooves (yellow arrows) are our compression rings, 1 ring in each groove.

The bottom groove (blue arrow) holds our oil control rings. There are 3 rings in that groove. (No rings in my pic, sorry. That was one I took after cleaning a piston.)


So, if you've got oil on all of your spark plugs from bad oil control rings, you are talking about the failure of 3 oil control rings on each of 8 pistons. 3 times 8 = 24 ring failures!

That would seem unusual after a quality rebuild.

Of course, the leakdown test will pinpoint your culprit, if any leakage is substantial enough to be that culprit.






*the top 2 compression rings extend out from those grooves, width-wise. That's what comes closest to the cylinder walls. The bottom 3 oil control rings do not extend out as far.

 

Yep, agreed, I did the rebuild myself and am 99% sure I put all the rings together correctly. I coated the bores lightly with wd40 - no oil - as per advise I've received. I agree that failure on all of them in unlikely, the part I'm worried about is revving the engine to 4k RPM almost immediately on initial break-in, and that could have caused them all not to seat correctly.

Leak down test will still only test the compression rings though, the oil control rings could be shattered and leak-down could still be good.

 

I wonder that if all the oil rings were installed wrong, that much oil could pass them?
As in, the ring gaps oriented incorrectly, all gaps lined up.
Using a clock face as an example, and 9 o'clock pointing towards the front of the engine, the middle oil ring should point to 3, and the top and bottom scraper rings at 1 and 5.
Top 2 compression ring gaps should point to 7 and 11.

 

Yeah that sounds right to me! Can't verify this without pulling the pistons though... so I'm going to focus on the leak down test, renewing the plugs and injectors, and testing for leaks (vacuum, exhaust back-pressure, fuel pressure) and go from there. When I pull the plugs I'll try to check if the cylinder walls are glazed

For the oil burning, I need to do a proper 200 mile freeway drive and test it again. I've been doing a lot of offroading which skews the results.

Along with all of that, I'm rebuilding the transfer case with 1.41 high gears, who knows this may also solve my problem, allowing me to pull higher gears at lower RPM.

 

I can't see the oil burning causing noticeable power loss, unless it was contstantly pouring smoke and misfiring from fouled plugs(which it isn't).
I wonder if you don't have 2 seperate issues, related or not.