1991 - G20 Beauville with a 5.7 l engine cil 4 n 7 are not firing properly Changed spark plugs cleaned up distributer cap and wires n still have the problem?

hi there double check your plug leads are in the correct order, also with the engine cover off, run the engine when dark and look for any arching from the plug leads to the engine. if none of these are found to be the problem then you could need head gaskets replacing (poss cause water leaking into cylinder bores.) hope this is of help and best of luck in it being the first solutions nate