Come on now. You don't really think we're that good, do you? :) If we could diagnose it over a computer, your mechanic would be out of work. He will perform some tests to determine the cause and course of action. We can't see or hear it. He will probably start with a compression test. If it is low in that one cylinder he will listen for any unusual noises which could indicate a cracked piston, (dig deep into your wallet), a bent valve, (still fairly expensive), or perhaps a broken rocker arm, (not quite so expensive). While a compression test will verify the compression is low, a cylinder leakage test will identify the cause. Compressed air is pumped in through the spark plug hole, then you listen in four places to determine where it is leaking out. A common problem on Fords is a leaking head gasket but there still should be SOME compression. Now, that description pertains to a loss of compression. You used the term "combustion" which many people use incorrectly when they mean compression. If you really meant combustion, that would imply the dead cylinder is fine mechanically, just that it isn't firing and contributing any power. That's going to be a whole lot less expensive. Basically you have a spark plug or an injector that isn't working. Both are driven by the Engine Computer which could be defective, but there's a lot of much less expensive things that are more common causes.
Wednesday, March 9th, 2011 AT 10:46 PM