I have a 1997 Ranger 4x4 4.0L automatic. I have replaced the spark plugs and wires, fuel filter, and PCV valve all within the last 2 years. I also installed a Screaming Demon coil pack and gapped a new set of plugs to 0.063 two years ago. Twice within the last week or so when I started my truck in the morning it ran real rough, like it's misfiring or only running on 5 cylinders. It's misfiring so bad that it makes my truck shake and also bucks when I drive it. It does this when it's idling, accelerating, and cruising and in all gears, but seems to buck worse in 4th and 5th gear. What's weird is that it goes away shortly after my truck warms up and then my truck will run fine. It has done this to me once last week and did it again this morning. My truck has not thrown a check engine light unfortunately. I have read up on possible issues and I think that it might be a bad EGR valve, a fouled spark plug, or a bad fuel pressure regulator. It seems most likely to me to be a bad EGR valve, but I would assume that it would throw a check engine light. I'm just looking for other opinions before I spend the time and money on replacing parts while trying to chase down this issue.

 

Regap the plugs to .060 , check the insulators for cracks , and see if that helps.

 

mine dones this and i find that replacing spark plug #3 correct the issue. For some reason, this plug goes out every few months and when I replace it all is well.

 

I have a 2000 4.0 and had this same problem. You may want to check your O2 sensor and intake manifold gasket. Those were the 2 things I had to replace and the truck runs great now.

I did have a CEL: Misfire on cylinder #3 that would come and go. When it first started acting up it would idle/run rough on a cold start then smooth out after a few minutes. After a while it got worse until it was rough all the time. Good luck.

 

Wirelessly posted

I'd check the O2 sensor. Recently same thing happened to me. No codes but I found that the last O2sensor was loose.