car shaking?

car started shaking hard when i started it up earlier today. it feels like its coming from under the body. any help would be great.

Maybe was running on less than 4 cylinders, my friends car vibrated a lot when it was running on 4 cyl. (2 dead on one side).

Always found thta symptom to be a leaky lower injector O ring.

i started pulling spark plug wires and found that the third cylender isnt firing. the spark plug itself is fine. as well as the wire. the distributor cap is fine as well ,so whats next? should i take the head off and check the cylender or is their someting i'm forgetting to check?

also. to check the injector O ring, do i just pull the fuel rail out and check it?

What does the plug look like? If it is carbon'd up, then you can bet the injector o ring is bad. Check for spark on that plug as well. If spark is there, o ring is bad.