Great deals on TJ parts on Amazon!

Looking for parts for your Jeep Wrangler TJ? Checkout the selection of TJ parts Amazon has to offer, many with 2-day Prime shipping!

Click the image below to browse TJ parts on Amazon.

Jeep Wrangler TJ Parts on Amazon

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.

TJ misfiring

KimsJeep

TJ Addict
Supporting Member
Joined
Jan 5, 2019
Messages
1,705
Location
Sacramento
In the "what did you do to your TJ" thread I mentioned I "fixed" my check engine light problem. The light came on and the code reader said "cylinder 1misfire". At that time, I thought it was a loose connection from the wire to the spark plug. It ran fine after I pushed it back on. Well, today it started missing again and the light came back on. Same exact code, P301 cylinder 1 misfire. This time I pulled the plug.

DFD5DC0C-4A16-4127-81A9-7005E01E5CDE.jpeg
E658CFA8-0D29-4701-A3F8-AC15071FAADE.jpeg


I checked the gap and it was a little over .040. I ran it across the wire wheel then set the gap at .035 after doing a quick google search for the correct gap. While I was putting the plug back in, hubby came out to see how I was doing and said I should check the cap, so he pulled it off to look at it. Ended up going to the parts store and getting a new cap and rotor.

D604F474-2F22-463F-805E-5C3DE3C66D88.jpeg
5D4F1DFA-0A8C-4888-8080-8B1F792DAAEA.jpeg


Put it all back together and was excited to start it up and see how smooth it ran. It didn't. :( So, I pulled the rest of the plugs an regapped and wire wheeled them and put them back in. Still didn't sound all that great. Hubby was back out by that time and he said he felt like the cap was not on right, so he loosened it and retightend it down. I then switched the number one wire with the number 4 wire. Figuring that if it still had a miss I would check the code reader and see if it would through a different code. I figured if it threw the 301 code again, it has to be the plug, but if it threw the number 4 cylinder code, it was the wires.

Although, it appears I will be buying new plugs. As I was typing this all up and uploading the pics, I noticed that in this next pic, the middle plug appears to be broken. This plug is not the number 1 cylinder plug though.
BCD07575-67E0-4641-85AA-C7EE9650C5C1.jpeg


As you can see, these plugs were Champion (looks like) RC12ECC. I'm going to go check out the thread about plugs and see what I should buy. :D

I guess I might as well get new wires while I'm at it. Although, all the plugs, wires, cap, and rotor are only about a year and half to almost 2 years old. Should they last longer then that? I haven't had to replace any of those things that soon on any of my other cars. Maybe I drive the Jeep too hard? LOL
 

Steel City 06

TJ Expert
Supporting Member
Joined
Mar 12, 2019
Messages
4,246
Location
Pittsburgh, PA
Try the Autolite XP985. Those plugs will work for 99% of TJ owners. RockAuto and Amazon usually have them at a good price.

If you spend most of your time at high throttle or climbing a lot of hills, the Autolite XP5405 might also work. They're the same plug as above but colder. I recommend trying the XP985 first though, especially if you're more of an average driver.
 
  • Like
Reactions: Modoc Guy
OP
KimsJeep

KimsJeep

TJ Addict
Supporting Member
Joined
Jan 5, 2019
Messages
1,705
Location
Sacramento
Try the Autolite XP985. Those plugs will work for 99% of TJ owners. RockAuto and Amazon usually have them at a good price.

If you spend most of your time at high throttle or climbing a lot of hills, the Autolite XP5405 might also work. They're the same plug as above but colder. I recommend trying the XP985 first though, especially if you're more of an average driver.
Thanks, that is the one I saw was recommended. They will be here Wed. :D
 
  • Like
Reactions: Jerry Bransford

pagrey

TJ Guru
Supporting Member
Joined
Apr 10, 2018
Messages
7,143
Location
Los Angeles, CA, USA
Personally I never gap plugs, if they are damaged in the package return them. They are set at the factory, if they are worn then replace them. The damage in the ceramic will cause arcing where you don't want it, that's another reason not to stick metal objects into plugs and pry on them or take a wire wheel to them. These things are less than a beer, buy a six pack when you need it.
 

taylormade73

Mr. Shimmies
Supporting Member
Joined
May 1, 2019
Messages
3,683
Location
Miami Valley
Personally I never gap plugs, if they are damaged in the package return them. They are set at the factory, if they are worn then replace them. The damage in the ceramic will cause arcing where you don't want it, that's another reason not to stick metal objects into plugs and pry on them or take a wire wheel to them. These things are less than a beer, buy a six pack when you need it.
From Autolite's website
Screenshot_20210914-000441_Chrome.jpg
 

pagrey

TJ Guru
Supporting Member
Joined
Apr 10, 2018
Messages
7,143
Location
Los Angeles, CA, USA
I've read both ways from different spark plug manufacturers, do what you feel is best. The crack here in that plug is a good example of why force on the plug isn't great. I personally run NGK and they say don't but like I said do what you want.

Edit: also worth noting NGK specifically says "Gapping should never be attempted on multi-ground plugs." which is what most of us fancy waste fire engines run
 
Last edited:

taylormade73

Mr. Shimmies
Supporting Member
Joined
May 1, 2019
Messages
3,683
Location
Miami Valley
I've read both ways from different spark plug manufacturers, do what you feel is best. The crack here in that plug is a good example of why force on the plug isn't great. I personally run NGK and they say don't but like I said do what you want.

Edit: also worth noting NGK specifically says "Gapping should never be attempted on multi-ground plugs." which is what most of us fancy waste fire engines run
Screenshot_20210914-001419_Chrome.jpg
 

taylormade73

Mr. Shimmies
Supporting Member
Joined
May 1, 2019
Messages
3,683
Location
Miami Valley
2 of the 6 plugs I installed last year had to be re-gapped. What was I supposed to do? Keep returning them until I got ones properly gapped?
 
  • Like
Reactions: tworley

pagrey

TJ Guru
Supporting Member
Joined
Apr 10, 2018
Messages
7,143
Location
Los Angeles, CA, USA
I would return them but I'm not you. Mine all have come with a cardboard sleeve and have always been good. If the plug was damaged in shipping it's damaged, why install it? You could get cracks like the ones here. Our plugs which have nothing to do with this thread make two sparks, I don't personally know how to set the gap so both sparks are the same length but I think they are set correctly at the factory. If you are okay gaping them then do it. This is one of those deals, I really do think gaping plugs is a waste of time for a $2 part. If they are worn get new ones, if they are bent from the factory then return them.
 

taylormade73

Mr. Shimmies
Supporting Member
Joined
May 1, 2019
Messages
3,683
Location
Miami Valley
I would return them but I'm not you. Mine all have come with a cardboard sleeve and have always been good. If the plug was damaged in shipping it's damaged, why install it? You could get cracks like the ones here. Our plugs which have nothing to do with this thread make two sparks, I don't personally know how to set the gap so both sparks are the same length but I think they are set correctly at the factory. If you are okay gaping them then do it. This is one of those deals, I really do think gaping plugs is a waste of time for a $2 part. If they are worn get new ones, if they are bent from the factory then return them.
I'm aware that our TJs are waste fire. I'm confused on the reference of multi ground plugs though. My plugs look like hers and not like any pics or diagrams of multi ground plugs which appear to have more than one ground electrode. Are you saying that your using multi ground plugs with more than one ground elestrodes? Or that there are multi ground plugs that have one ground electrode and look like Kim's plugs?
 

Steel City 06

TJ Expert
Supporting Member
Joined
Mar 12, 2019
Messages
4,246
Location
Pittsburgh, PA
I’ve had no issues re-gapping the Autolite plugs or any other brand. The one thing to be careful with is not to hit the ground electrode off any geometry while inserting the plug into the hole.

The XP985 I believe came pretty close but slightly over 0.35, but a bit of adjustment and had no issues. THE XP5405 plugs I just put in were well over 0.35. Again, no issues shortening the gap.

That said, I wouldn’t recommend re-gapping used plugs more than once, and to replace them if the history is unknown. Like a paper clip, there is only so much yielding the base material can withstand before it gets weak and breaks.

All TJ spark plugs I’ve seen are single-ground.
 
  • Like
Reactions: taylormade73

pagrey

TJ Guru
Supporting Member
Joined
Apr 10, 2018
Messages
7,143
Location
Los Angeles, CA, USA
I gap plugs on my 1960 Ford because they are used in several different vehicles with different power ignition systems that require different gaps. They don't come with the correct gap. I don't in the TJ because no TJ ever has been fitted with a spark plug that is used in a different vehicle that has a different suggested gap. If you get the correct part number the gap is correct unless the plug has been damaged and that is obvious, and I personally wouldn't install it. The Ford also has points and I adjust those when I feel like it, most people suggest I change to an electronic system and dump the points without ever having used a dwell meter, guess you gotta live with the noise. Most DIY mechanics use the wrong specs for the wrong plug and gap incorrectly making things worse. It's not a big deal but that's why I suggest inspecting for damage and simply installing and will continue to do so.

The geometry of the spark on the newer factory v-power plug and iridium and platinum plug and how that relates to their gap from the factory has nothing to do with this discussion. If you measure with feeler gauge 20 of one type and 20 of another type you'll notice something interesting and probably grumble that our society is dying.

Obviously there's no way I can post this information for any mechanic that might be interested without generally making the old school mechanic groan a bit. Regarding this thread our service manual specifically says the most common cause of this damage

crack.jpg


is bending the electrode while adjusting the spark plug gap. I thought it was relevant, but also enjoy reading the comments, especially the "you'll kill baby sea turtles if you don't mind the gap."
 
  • Dislike
Reactions: Matt131
OP
KimsJeep

KimsJeep

TJ Addict
Supporting Member
Joined
Jan 5, 2019
Messages
1,705
Location
Sacramento
Bringing this thread back to life. My random misfire on cyl. 1 has come back. Actually, I started getting a miss this morning. I got home and put the new wires I had ordered last week, on. I started it up and the check engine light came on. LOL Wasn't on the whole way home. It seemed to run better, but could still feel it miss ever so slightly.

I put the code reader on it, and it is the same code. P301 Cyl. 1 Misfire detected. The top reported fix is 1: clean the engine carbon or 2. change the plugs (did the plugs and now wires) I think I cleaned the intake thingy a year or so ago. I think? LOL I know I did it on my Liberty and I could have sworn I did it on the TJ too. I may try cleaning it again just for good measure.

I noticed while going through some of the other "reported fixes" it mentioned that replaced clock spring was a fix. Reason that caught my eye was because I have been having some issues with my headlights going off randomly after I pull the switch to turn them off. I was thinking it was probably my switch going out, but then a couple times I would turn my brights on and when I turned them back off, the headlights would shut off. I'm thinking that the clock spring would be the issue with that. What do you guy's think? If it is the clock spring causing the headlight issue, then maybe it is also causing my mis on cyl 1? Oh, I have to play with the headlight switch and I can get the headlights to come back on.

Anyone else have a clock spring that caused a misfire??
 

aston4

Member
Joined
May 1, 2020
Messages
40
Location
Nm
I think the chance of misfire being caused by clockspring is very close to zero.

You can remove the clockspring entirely on any '97 onwards Tj/xj and the engine will run just fine, though the airbag warning lamp will come on.

You mentioned new wires and cap/rotor, are they actually installed? Is there something loose regarding the actual distributor? Try wiggling the distributor itself. Look at the engine running in pitch blackness after your eyes have adjusted to darkness - are there any electrical sparks around the ignition wires leaking about?

At a certain point you may just need to take it to an experienced mechanic who often can diagnose problems like this in a few minutes - think of it as paying a few bucks for the education. A misfiring engine is a bad, bad thing, can quickly destroy your catalytic converter, valves, etc.

Also, if you have the old style knob that you pull and push in and out headlight switch, those things fail constantly as you describe. Just get another off ebay for $20 and watch a few install vids on utube. It's a simple 30 minute job first time, 10 minute install every time thereafter. The replacement will eventually fail too. Chrysler engineering's finest.

Also all non-plug gappers are going directly to hell.
 
  • Like
Reactions: Blondie70
OP
KimsJeep

KimsJeep

TJ Addict
Supporting Member
Joined
Jan 5, 2019
Messages
1,705
Location
Sacramento
I think the chance of misfire being caused by clockspring is very close to zero.

You can remove the clockspring entirely on any '97 onwards Tj/xj and the engine will run just fine, though the airbag warning lamp will come on.

You mentioned new wires and cap/rotor, are they actually installed? Is there something loose regarding the actual distributor? Try wiggling the distributor itself. Look at the engine running in pitch blackness after your eyes have adjusted to darkness - are there any electrical sparks around the ignition wires leaking about?

At a certain point you may just need to take it to an experienced mechanic who often can diagnose problems like this in a few minutes - think of it as paying a few bucks for the education. A misfiring engine is a bad, bad thing, can quickly destroy your catalytic converter, valves, etc.

Also, if you have the old style knob that you pull and push in and out headlight switch, those things fail constantly as you describe. Just get another off ebay for $20 and watch a few install vids on utube. It's a simple 30 minute job first time, 10 minute install every time thereafter. The replacement will eventually fail too. Chrysler engineering's finest.

Also all non-plug gappers are going directly to hell.
Yes, I put the new plugs and cap and rotor in. Today I put the wires on. I will go check of anything loose.

The puzzling part is it comes and goes. It will run fine for a while. Start it up the next day and it is missing, then drive it to work, shut it off, get off work and start it up and the miss is gone again. Well, at least I can't feel it missing. Maybe it is but just enough that I can't feel it??
 
OP
KimsJeep

KimsJeep

TJ Addict
Supporting Member
Joined
Jan 5, 2019
Messages
1,705
Location
Sacramento
Ok, I went out and wiggled wires, then I figured, what the heck, I'll try unplugging the injector wires. Well, I unplugged the first one and didn't notice any change what so ever. Plugged it back in and unplugged the next one, and there was a definite change. I took a video but you really have to listen to hear the change. I can hear it better with my ear then I can on my phone. The phone pics up the fan noise making it harder to hear. Anyway, I think I may have a bad injector?

 
  • Like
Reactions: Blondie70