Ok an update on the mystery misfire. I have been chasing this one for a long time as you can see from the posts. My condition came to halt about a month ago when the engine quit on my drive home. Timing belt snaped while at cruse. Installed new belt, idler, water pump. Thought I would dive into this misfire again as my milage dropped to 18 mpg from 28 and the power has also droped. I have read many other posts in a few forums with the same problem and no real answer, I dont know if they gave up or what. Other post have suggested a bad computer because the coil driver is in the computer. Others say crank position sensor. Well ad those to the list of new parts (except the computer, I found a used one for $75). Plugged exhaust was also mentioned. I unbolted that and the same problem. I did a compression test and 185-180 on all 4 cyclinders. I keep thowing missfire cyl #4 and some times #2. I kept driving untill it was hard for anyone to drive it as it stalled every time the throttle was snapped closed like when you push in the clutch to come to a stop.
I pulled the head off to take a look and did not see anything obvious like blown gasket or crack between valves. I took it to the machine shop and he said I can see your problem right here. Your exhaust valve seats have recessed.
Read this article: The Misfiring Ranger Mystery
My guy at the machine shop explained it to me and it makes sense. The 2.5 has a lifter to take the slack out of the valve train and as the valve seats wear and recess the valve lash that the lifter takes up is now gone and the lifter bottoms out. Eventually the valve hangs open this happen only when running as the oil pressure pumps the lifter up and opens it even farther but only when running. When the engine is off to do a compression test the oil pressure is zero and not pumping the lifter up. When I looked at the valve and compared it to the other valves it looks like the exhaust valve in the #4 cylinder sits 1/8 inch deeper in the seat than all the others.
After reading the article I wonder why my ford dealer did not check for TSB's
I will post after I get it back together. The shop will not have the head ready until Friday or Monday.