What causes miss-firing on 8 cylinder?

Could be,A fouled/worn spark plug(s),

A faulty spark plug wire(s),

A bad distributor cap and rotor,

Incorrect firing order,

Moisture inside distributor cap,

A bad fuel injector(s) if applicable,

A burned valve(s),

Contaminated fuel (water in gas),

Incorrect fuel pressure,

Dirty/plugged fuel filter,

A failing fuel pump,

A vacuum leak,

The year, make and engine info would help for more possibilities.