So last weekend I did a quick lil tune up in my jeep(99 4.0l AW4 3.5 inches 31" tires). I did plugs, wires, oil change, and a coolant flush. Everything went fine, Ive done this stuff tons of time. The old plugs were shot. I replaced them with champion plugs, I hear theyre a good replacment and it had champions in it before. So I do new plugs and wires. Start it up and all seems fine, good, job well done. So later that night I was sitting in traffic, idling in drive. Every now and then the motor kinda stumbles. Its hard to describe, the revs drop a lil and it idles a lil rough. I notice too the on take offs and in reveres it feels like theres a lack of power. I have also noticed that the gas milage has gone way down hill. I baby it to get the most milage I can. Easy take offs, keep it at the speed limit. So what do you guys think is the culprit here?
Matt

 

don't take this wrong, but make sure the firing order is right. also if you do the plugs and wires, do the cap and rotor, no reason to do one without the other, then you get a problem like this later and wonder what it is.

next is check your plugs. could've accidentally dropped one and crushed the gap. my last trip to the badlands a guy in a tj had his jeep running rough, misfiring. he just tuned it up before the trip, we checked the order, then i asked him is it possible you dropped a plug? he said no way, didn't drop anything.

so after putsing around i finally say i'm checkin the plugs, second plug i pulled was smashed down with no gap, the other gaps were off. so all i'm saying with that story is check the gaps, you can't trust them out of the box either.

whenever you do something, and then you have a prob, first go back to what you just did. check firing order, wires are snapped on both ends, then plug gaps, and replace the cap and rotor.

 

had the same problem before on my chevrolet truck after I replaced the spark plugs and wires. I changed out the distributer cap and it fixed the problem. I guess during the replacement of the wires I might have put a small crack in the cap and it caused the engine to run really rough, like at anytime it would die.

 

Cap and rotor have now been replaced and double checked the gap of the plugs. It seems to idle rougher now. Kinda sputters or shutters at idle. Sputters on take off. Could it be the coil?

 

bump

 

Probably not the coil. They either work or they don't. Like being pregnant you either are or you're not.
Gotta be a wire arcing or a cracked cap or a carboned up rotor. The plugs also bear re-checking. Look at the engine running in total darkness and see if you detect and spark or arcing.

 

you double checked the firing order? all wires are plugged in? cap is on the distributor straight, if thats all good then check the insides of the wires for cracks on the metal pieces, were they quality parts or some cheap ebay stuff?