this is the 2nd 4.3 ive gotten wiht a dead #5 cylinder both motors had/have high mileage but seem to run good and have suffecient power none the less. the last motor i tore down and found NOTHING wrong with it. valves were good and functioning con rod was intact piston was in good shape everything was fine. since before the tear down i had replaced the rotor cap plugs and wires i knew that wasnt the problem either.

well ive got another 4.3 dead on #5 changed the plugs and plug wires cap all that good stuff still dead. im not going to tear this one down because i suspect nothing is wrong inside the motor because of the last time.

sdoes anyone know why these motors do this?

 

Could be a bad fuel injector, bad cam lobe, or a vaccum leak or a bad O2 sensor