I just got a 97' F-150 a year ago and it ran wonderfully with 120,000 miles on it. About two months ago the engine started to pop and misfire when ever I would try to accelrate quickly. I replaced the plug wires and it went away for about two weeks then came back. and its not there all the time, it will range from missing every time I go to accelrate hard, to not at all. any help would be greate, thanks,

1997 F-150, 4.2V6, 125,000 miles.

 

What codes are stored? A random missfire is different from a specific cylinder, for cause..

 

its not throwing a code yet but last time before I replaced the wires it was a misfire on 6

 

Sounds like there was two problems and you fixed one.
There are a number of other faults that could cause the apparent miss under acceleration.
The point of no codes is that it is random and not in long enough to set a code if it clears at idle etc.
EGR operation fault, fuel pressure drop, mass air meter operation are the ones I would look at first for causing a lean condition.
Every engine needs a richer fuel mix for acceleration. Not having it results in a missfire, and gone to extremes, will usually pop/backfire through the intake.

 

Thanks, I just cleand the MAF sensor and EGR and replaced the old K&N Air filter (that was faling apart) with a new Airhog and the truck runs better than ever.