| Long Story: I started my Z up last week and it was immediately missing on one cylinder. I traced it to cylinder 6 via a power balance test. The injectors ohmed correctly, ticked and sprayed fuel. There was a good spark also. So I did a warm, wot compression test, showed 110psi for that cylinder. Adding oil did not change the value. I checked all of the other cylinders and they were at 160psi. For some reason when the engine was cooled off I checked compression again and found that it had dropped down to 60psi. I hooked up an additional battery to make sure that it was not getting slower at spinning over. Short story: Low compression in cyl 6 (60psi)
Adding oil did not raise compression I need help figuring out what the cause is, I thought it would be fairly obvious like a stuck valve or cracked ring land. One thing that strikes me as weird is the scraper ring (2nd) on cyl6 piston doesn't seem to be wearing evenly, there is not an even shiny part all the way around like there is on the compression ring. The bore looks good to me. Also there seems to be a lot of carbon build up for 10k kms since the last rebuild. I pulled the cams out, filled the combustion chambers up with water and used my airgun on the backside of the valves. One of the intake and one of the exhaust valves make bubbles on cyl 6. Would this cause over 100psi loss? None of the others do that except cyl2 intake valve has about half or less as much bubbles. 
Only one mark on the piston, isn't too pronounced but it catches a fingernail slightly.
How do these look for 10k kms (5w40 rotella t6 used)
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Low compression diagnosis - 
