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dcrolin 01-15-2006 02:31 AM

Bad Plugs?
Hello Everyone...I have a 97 TJ 4.0 AT with 135K miles...Here is my problem...I just got a CEL code 301 -- Cylinder #1 misfire. So I replaced the #1 plug and CEL went away. About 6 months ago I had the same problem...same solution...same result. My question is what would be causing my #1 plug to do this. I did a complete tune-up 6 months plugs, wires, cap, rotor. Could it be a bad injector?? Why just #1 plug foul?? Any insight would be greatly appreciated. Thanks

Fapple 01-15-2006 10:45 AM

I have had the same problem with my 2003 TJ. I was going up a hill in 5th gear talking to the wife, should have down shifted but hadn't yet, just mashed harder on the gas peddle. then the check engine light came on. It was also a #1 cylinder misfire. I did not change the sparkplug, I just reset the computer. it's been 7-8 months now with no problem. I wrote it off as an computer (or software) glitch. When is your light coming on, is it during a heavy load on the engine? When you change your plug is it actually fouled? I have an OBDII scanner and when I hook it up to my Chevy Tahoe it gives me a count of how many times each cylinder has misfired. The point is misfires are not a problem... too many misfires are a problem. Who knows what the algorithm is that the Jeep computer is using to turn on the check engine light for misfires. If it happens again (if I were you) I would try an experiment. I would just reset the computer and see how long it takes to get check engine light again.

Well, good luck keep us posted...Thanks,

Jerry Bransford 01-15-2006 12:23 PM

Some 97/early 98 4.0L engines had bad valve springs installed from a bad batch. If this problem persists, that is likely your engine's real problem. The dealer has a TSB for it which basically just replaces the valve springs.

dcrolin 01-16-2006 04:38 AM

The CEL just came back on today...I'm assuming its the same code...I don't have a scanner...and I haven't had time to take it to Autozone for the read. As far as the plug being fouled, when I changed the plug the other day...the one I took out (installed 6 months ago) was worn at the tip...there were no deposits, but the tip was just rounded and worn down. reset the computer, just unplug negative terminal or is there a hazard fuse I should pull?? B/C I always unplug negative terminal when doing work so that should have reset the ECU. Also could the constant CEL be from not having enough torque on the plug...b/c this time when I replaced the plug I didn't torque to spec....The #1 plug is hard enough to get at w/ a hinged socket adapter but I've already broke the porcelan before trying to torque. Thanks for the input and keep it comin.

dcrolin 01-16-2006 04:48 AM

Also, about the TSB... I'm not sure how they work, I am not the original owner, so could I still take it to the dealership and they would do it for free? Thanks

Jerry Bransford 01-16-2006 11:53 AM


Originally Posted by dcrolin
Also, about the TSB... I'm not sure how they work, I am not the original owner, so could I still take it to the dealership and they would do it for free? Thanks

TSBs are not the same as a Recall. Recalls are always done for free whether or not the vehicle is under warranty. Recalls are for serious defects, usually safety related. TSBs are a Technical Service Bulletin that offers the dealer a prescribed method to fix a common problem and but are not free unless it's under warranty.

Your TJ is newer so it's hard to say if the weak valve spring batch problem is the source of your misfire as it was for my '97.

dcrolin 01-17-2006 05:22 AM

Mine is a 97...Sahara model...AT...Now I am getting a noise for a few seconds when I put it in reverse right after start up....cold weather start up. Could this be related??

dcrolin 01-18-2006 08:17 AM

Any suggestions or fixes for this code 43 I am getting??

Jerry Bransford 01-18-2006 10:56 AM


Originally Posted by dcrolin
Any suggestions or fixes for this code 43 I am getting??

Only the same one I already suggested to you above. There is usually no other fix for repeated 43 codes.

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