A burnt engine valve causes a car to lose power, misfire, backfire or idle roughly. Fuel consumption can go up, and the exhaust system may develop a "putt-putt" sound. These symptoms get progressively worse until the valve is repaired or the engine suffers major damage.
Burnt valves can be caused by excessive localized heat, irregular valve sealing, faulty valves or incorrect valve clearances. Hot combustion gases leaking out in a concentrated area damage a valve, eating away the metal. Mechanics make a preliminary diagnosis of burnt valves by listening to the engine or by the pressure at the tailpipe. A compression test can confirm a leaking or burnt valve.