1989 CRX DX. stock everything. No compression on #3 (i mean the needle doesnt even flicker) I put a cap full of oil in the cylinder and got the needle to flicker but not to a readable amount, maybe like 3-4 psi. I've seen blown engines before but they usually make at least a little compression. It was running fine, and then all the sudden it only ran on three cylinders. What do you guys think it could be? Melted valves? Hole in the piston?

 

sounds like the piston is gone

 

do a leak down test.

pressurize the cyl.

if it leaks from the intake manifold = bad intake valve
if it leaks from the exhaust ports = bad exhaust valve
if your coolant bubbles = bad headgasket/cracked sleeve
if it comes out the oil filler cap = bad rings/no piston