94 xj6 misfire and valve noise

My 94 xj6 developed a problem when driving, it misfires on the last cylinder randomly, every couple of seconds the engine starts shaking violently. I found that the last cylinder was not contributing, it has spark and fuel. There is a sound near that cylinder that sounds like tapping on a tin can. I was thinking a bad valve maybe.


How did you find that "the last cylinder was not contributing"?

Have you done a compression test on that cylinder?

This is strange, I just did a compression test on all cylinders and they are all 20 psi.

Nevermind my tester was not working, all cylinders actually have 190psi