With the engine running, disconnect one spark plug wire at a time until engine sound does not change; that identifies a dead cylinder. Inspect and test that plug and wire, noting a plug can fail even if it looks fine. Swap the plug with one from another cylinder to see if the miss follows it. A general tune-up with new plugs, wires, cap, rotor, and air cleaner was also suggested; if the miss remains, continue diagnosis.
The owner reports a van with a 350 small-block Chevy that constantly misfires and has no power. Compression tested good, but the number of missing cylinders is unknown. An expert advised pulling plug wires one at a time to find the cylinder that does not change engine sound, then checking that plug and wire or swapping plugs to see if the miss moves. Another reply recommended a general tune-up with new wires, cap, rotor, plugs, and air cleaner, then further diagnosis if the miss continues.
