I've heard of people using these plugs in their cars and getting more power and mpg's with no other problems. Two of my friends used them and haven't complained. I've also read some reviews of people using these plugs and having nothing but problems, so im stuck on what to choose. Are E3 plugs fine to work in the 4.0 or are they nothing but problems? Are there any other recommended plugs i should use? i have an older 89 4.0, so its not the H.O. right now im averaging 5mpg and not much power its really pissing me off

Don't do it. You want Champion Copper plugs

I have e3s in mine and havent had any problems can't say there is a noticeable power difference but my mpg seems to have gone up

I've seen no data on actual gains. Some have reported misfires with the E3 (and Bosch), which have gone away when switched back to Champion plugs.

I continue to recommend conventional copper plugs for the Jeep 4.0 engine.

*87-99: Champion copper

*00-01: NGK copper (last a bit longer than Champions with the coil pack ignition)

BTW, if you are averaging 5 mpg, it is likely not the fault of the plugs alone. Start with a complete tuneup including plugs, wires, cap, rotor, fuel filter. Then see where you are at after that.

If mileage still sucks, start testing stuff. Here is HOW to test a lot of things on the 87-90 XJ:

http://www.lunghd.com/Tech_Articles/...iagnostics.htm

5mpg? You've got a LOT bigger problems than your spark plugs as tjwalker said.

These are simple engines that require simple spark plugs, champion coppers gapped to .035.

Thanks for all the info guys, its really a big help I definitely have some things to go through on my jeep. I really need to get better mileage, its killin my wallet. Any idea of how much the tuneup parts would cost?

Champion Copper Plugs: $1.99ea
Bosch Plug Wires: $24.99
Distributor Cap: $32.99

Total $70+tax

Prices via autozone. I didn't list the cheapest products but what would be ideal for your 4.0.

Consider changing your O2 sensors as well after doing some diagnostic work.

Supposedly E3's run better for the first few miles - then the inaudible detonation burns holes in the pistons.

They are touted as "High Performance" - they are - the high price the mfgr gets is for them!

Stick to non-gimmick plugs and parts.

how about Denso or Autolite copper plugs? Will those perform as well as the Champions or is there something specific about the Champions that makes them the "gotta have " plugs on your 4.0?

The 4.0 is a simple engine and requires simple plugs. You can try other plugs (I've tried 5-6 different kinds/brands over the years) but it's pretty commonly accepted that up to 99 you use Champion Coppers and the coil based ignitions 00-01 get NGK's.

Going back to me trying different plugs. I always end up mad at myself for experimenting and put new champions in the engine after a bit because the other plugs don't work well. I've had misfires after using different plugs, rough idle, problems starting; I've had none of those problems in either XJ using the Champions.

thanks xjsnake, ill go sometime this week and get plugs and maybe wires. ill spend as i go and see what ill need. definetly gettin new plugs soon tho. im pretty sure mine are shot.

I got an accel kit. rotor,cap,plugs,8mm wires. No probs for a whole year and a half now with a OEM coil.

I was looking at the E3s tho at one point.

If theres an Oreilly near you go with the borg warner nascar select cap, rotor and wires. They carry a life time warranty, Ive changed mine five or six times in six years.

I have msd wires and blaster coil platinum plugs Never no problems