Ford Repair: Engine misfire troubles, o2 sensors, engine misfire

Question
2,000 miles ago I replaced the motor in my '99 Ranger and had no problems with it for the first 1,000 miles. I now have a check engine light on. At first I replaced plugs and wires, then after Going to Autozone to read the codes, I replaced the O2 sensors. At this first code reading it said sylinder number five was misfiring. after working on it, it now says cylinder six is misfiring. I have run diagnostics on the coil pack, the wires, charging system, and compression, all are within specs. I hear what sounds like the valves slapping when the engine gets up to speed and I give it a little gas. Also, the tail pipe at times sucks in a rag held over it. I have been unable to find the main problem, can you help?

Answer
Michael,

If the tailpipe is sucking anything in you have a valve problem in the engine.  Most likely cause would be a broken valve spring.  Also, make sure the camshaft has not walked forward causing the wrong valves to open out of sync.

I would do a compression test and check the valve adjustment and springs.

Good Luck!!