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Well, I opened up the engine by taking the head and the sump off. I pushed the piston of cyl 3 out and it is stuck rings. Two of the rings are stuck to the grooves, jammed tight.
I also did 2 tests.
1) I did an ambient cold compression test, car has not been driven for almost 2 months. I was surprised that the reading is exactly the same as the hot compression test I did. It leads me to believe hot and cold test makes NO or very little difference.
Cyl 3 = 150 psi.
The others cyl range between 340 to 360psi. Almost identical to hot engine.
2) I poured SAME amount of oil into cyl 3 and 4, on top of the piston. I found cyl 3 drained into the sump much faster than 4. It is a very crude test but it gave me a clue that the rings may be bad before I removed the sump and pushed the piston out.
Also I remembered I changed out the injector on cyl 3 a while ago, may be a year. It was over dispensing. I think it was the reason that the ring was baked into the grooves. So much labor to fix a stuck ring. So test your injectors every 50K, no more than 100K miles. It will give you grieves if it over dispenses.
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