Hi folks, I am brand new here, having recently bought a one owner 1999 Cherokee Limited. It has been running very well, that is until tonight. I decided to start fresh with new plugs, wires, cap and rotor, even though the truck was running well. I gapped the plugs at .035, they're the same kind that I took out, Champion copper plus. The plugs really looked like they needed it, the gaps on them ranged from about .060 to .075 or so, although the color looked good (tan). I put it all back together and started it, and it's now running a bit rough, idle is hunting a little, and now the check engine light is on. Other than re-checking all the connections, etc., what should I check? What did I do wrong?

Many thanks,

Andy
Arvada, CO

 

this sounds dumb but are you sure that you got the wires back in the right places? if you have two crossed it will run like crap... also .035" is a little tight for a modern vehicle w/ electronic ignition, I have run .045" on my old Studebaker (with MoPar electronic ignition) and the wider gap seems to make it run better - theory is as long as it's not missing under heavy load the wider gap is good because you get a hotter spark that way. That is apparently the spec for a 4.0 but like I said it seems like it is conservative...

 

OK, solved now. I did some troubleshooting, and figured out that when I inserted #5 in the first time, somehow I first accidentally pushed it against the valve cover or something, causing the gap to completely close. I gapped it again to .035 and now running like a champ!

One question. After i did this, the check engine light was still on, so I figured I needed to take it to Autozone and reset it. On the way there, the CEL just went out and hasn't reappeared. In this situation, I assume you don't need to reset it?

Thanks!!

 

good job finding the problem. You were probably throwing a code for a misfire and I'm assuming that the code cleared when the problem was solved and then you drove it around for a while. Unless you have an emissions inspection coming up soon I wouldn't worry about it.

 

The code is now stored. It'll read once you take a scanner to it. So you'll need to clear it eventually. But I wouldn't worry about it until you had to smog it or take it in for an inspection