Cadillac Repair: Burnt Valve., cadillac sedan deville, torque converter

Question
I have a 1991 Cadillac Sedan DeVille with a 4.9 V-8 motor.  I have been told that I have a burnt valve on clyinder no. 4 in the vehicle.  A friend of mine, who at one time was an instructor for GM, tells me he has never seen a burnt valve in this type of motor.  Is a burnt valve common to a 4.9 with 73,000 miles on it.  When I am at higher speeds, the motor levels out but between 40 and 55 it is very, very rough running.

Thank you for any help you can render.   I have not had the time for a machine diagonistic check as yet.

Answer
A burnt valve would be extremly rare on this engine.

The reason for the rough engine between 40 and 55 is this is when your TORQUE CONVERTER CUTCH (overdrive) engages and will cause any type of abnormality in the engine to be felt much greater.

Get a compression and cylinder leakage test performed on the vehicle first to make sure we do not have an internal engine problem.

tom