i just picked up a 1996 civic lx with a spun bearing on a d16y7. So i just picked another engine up for 300 dollars with 60k on it. I drove it for 3 weeks, ran like a champ and got 40 mpg. Then started car up and started missing. then it just stopped firing on 4th cylinder. So i did a compression test,at 60. Added oil to cylinder and compression test went back to 160.

Checked the fuel injector/replaced. and checked spark..no problems.

so i ripped off the head and found no cracks or no bad head gasket, vavle was not sticking. so..ripped out the piston, rings were compeletly fine. There is one line of scoring..very small on piston skirt/cylinder wall. But top off piston had no carbon, as if antifreeze was getting in cylinder.

Thinking it was a small head gasket leak/stuck piston ring

Any ideas? i am completely stumped on this motor