Running on 3 cylinders!!!

[93GreenLX]

Well the guy at the automotive shop said that the exhaust pipe hitting my gas tank is due to the engine shaking so bad becausing it is missing. He said I am only running on three cylinders and should get it checked out. I put new plug/wires on about 1 1/2 years ago. What elso could cause this. Carbon build-up Any ideas?

 

[chaka]

Check your plugs, gapping, rotor, and cap. I know my cousin changed his plugs and one boot was not seated right. ate through it real quick leading to a miss on one cylinder.