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john -aka eauto
john -aka eauto, The Car Guy
Category: Saturn
Satisfied Customers: 16045
Experience:  ase tech 15 + years foreign domestic & european
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3rd cylinder misfiring; I have changed plugs, coil pack..fuel injector

Resolved Question:

3rd cylinder misfiring; I have changed plugs, coil pack and the fuel injector and the problem still exsists. what else could be the problem?
Submitted: 7 years ago.
Category: Saturn
Expert:  john -aka eauto replied 7 years ago.
it may have weak compression or a burnt valve. I would check compression check to verify if there is a internal issue
Customer: replied 7 years ago.
I had someone check compression, he stated it was good, he also changed the fuel injector but it did not fix prblem. So if it is not a burnt valve what else could cause this?
Expert:  john -aka eauto replied 7 years ago.

There are several reasons why valves burn. One is normal wear. As an engine accumulates miles, the constant pounding and thermal erosion wears away the metal on the face of the valve and seat. The exhaust valve sheds most of its heat through the seat, so when the face and seat become worn and the area of contact is reduced, the valve starts to run hot. Eventually the buildup of heat weakens the metal and pieces of it start to break or flake away. Once this happens, it forms a hot spot that accelerates the process all the more. The valve begins to leak and compression drops. The result is a weak or dead cylinder and a noticeable drop in engine power, smoothness and performance.

A bad exhaust valve will also increase exhaust emissions significantly because it allows unburned fuel to leak into the exhaust. High hydrocarbon (HC) emissions, therefore, may also be an indicator of a burned valve.

An exhaust valve can also burn if the valve lash closes up for some reason (improper lash adjustment, cam or lifter wear, a bent push rod, worn rocker arm or cam follower, etc.). The lack of lash (clearance) in the valvetrain prevents the valve from closing fully, which causes it to leak compression and overheat.

Valve burning can also be caused by any condition that makes the engine run hot or elevates combustion temperatures. This includes cooling problems, abnormal combustion like detonation or preignition, loss of exhaust gas recirculation (EGR), retarded ignition timing or lean fuel mixtures

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