Low compression in one cylinder (1 Viewer)

[ruskiyab]

Had a cylinder 4 misfire on a 200k mile LC. Swapped coils, no change, did a compression, 75psi in cylinder 4. Put a borescope in it, didn’t see anything obvious as far as burned valves go, piston looked good, bore looked good. Pulled the valve cover, nothing obvious there. Unfortunately, I lent out my leak down tester so I haven’t been able to do that yet.

The car sat for probably a year prior to this and supposedly ran great before it was parked. It does have what sounds like a lifter tick at idle, runs great above 1000 rpm. I wouldn’t think a collapsed lifter would cause this but I suppose crazier things have happened. Any guesses?

 

[GTV]

Definitely need to pressurize the cylinder to know where the leak is first.

 

[UncleJakeNZ]

That leak down tester is going to tell you a lot.

It could be rust on a valve seat face (or seat) from sitting with the valve open for so long. I've had the same issues with old Mercedes engines. I just drove it and it came right after a while... which of course is not best practice, but it did save removing the head to do a valve lapping job