Ok, so recently I just changed out my spark plugs, wires, cap and rotor on my 4 liter. The spark plugs were definitely in need of replacement. But the next time I ran it, I noticed it was missing at idle only, but as soon as I started giving it gas it was fine. So just today I cleaned up the throttle body and the breather valve things on top of the valve cover and theres still no change. Put in some fuel injector cleaner so still waiting to see how that affects it, but I'm kinda stumped. I don't have any vacuum leaks, and it doesn't miss that bad, just enough to annoy me. one of the reasons I notice is because the only thing restricting in my exhaust system from the headers down is a glass pack, so I hear lots

 

Did you gap the plugs and are you using champions? Yes it make's a differance read the tag underhood for info.g/l For gapping use feeler gauges or wire gapper's, not those POS round one's very inaccurate.

 

I did gap them with a feeler gauge and they came out to .035 which I believe is spec. Another thing is when I pulled the old ones out, they were over twice that spec! So I assumed the ecu would have to relearn a little how to run. But I disconnected the battery to reset it and it still does this. But I don't know what you mean by champions??

 

Champions are the brand of plugs

 

Oh I got some brand just from auto zone, forgot the brand name haha. As far as I know it doesn't make too much of a difference

 

You will be surprised by the differance it makes, most guys and gals on here have tried other plugs but go back to the factory plugs cause they just run better in a 4.0. But do what you want.

 

It can make a difference.

For 87-99: Champion coppers

For 00-01: I prefer NGK copper. Champion will work fine, but they have a tendency to open the gap up quicker over time than the NGK does with the ignition system on the 00-01.

Do not use E3 plugs and do not use Bosch plugs. The hype you hear on Saturday morning horsepower TV doesn't apply to the Jeep 4.0 engine. I've helped others with mysterious misfires using these brands that were completely resolved when they switched to Champion or NGK.

 

Ok, I know I didn't get e3 or bosch. But I did get platinum plugs. the thing is I replaced the plugs with the exact same ones. I think I'll give champion coppers a try

 

I have a 94 cherokee by the way