Missing after tuneup

Planepal

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May 8, 2023
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Clarkdale AZ
So I sold my 1976 International Scout and am the proud owner of a 2004 Rubicon TJ with 5 speed manual and 51,000 miles. It’s in great shape with a 3 inch lift and the Banks Power System. It seemed a little sluggish on the test ride, I guess I was expecting a little more power out of it since that Banks System supposedly adds 29 HP to the motor with a header and free flowing exhaust etc. I bought and installed a new serpentine belt and a new set of plugs. The kid at Napa sold me Autolite APP 985 plugs. The gap was preset at .9mm Which is .035 inches Which I thought was correct. It also had a cold air intake with a K&N type air filter. The old plugs were original I’m sure as they were worn but They all were slightly fouled and the gap was around .065 Due to wear. The Pics are of one of the old plugs and one side is nice and tan but the other side is slightly fouled and all the plugs were similar. The air filter was filthy and had absolutely no oil on it. Just prior to tuning it up I had a check engine light and the code showed a bad TPS (throttle position sensor). Welcome to the new age as my Scouts TPS was my heel LOL. I thought I would tune it up and see if the code was caused by old plugs or dirty air filter. I installed the new plugs and cleaned the air filter and Wow! Big difference. A lot more power and it ran nicely for about 5 miles then it developed a sudden miss and loss of power. I thought maybe the TPS was to blame so I bought and installed a Mopar TPS but it’s still missing and the check engine light came back on. I have to go out of town for a few days but I guess I’ll pull the plugs and check them and then limp down to the auto parts store and have them check the code. After looking at some old posts, the gap went up to .04 inches on the motors with the electronic ignition rail which I have. I don’t think that amount of gap error would cause the misfire I’m having but I guess I’ll reset the gap to .04 and see if that helps.

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The Autolite APP-985 spark plugs are not the reason for it missing now, that's a good choice for your model year. I'd be suspicious that perhaps the coil rail boots didn't make it all the way onto each spark plug correctly which has happened to me. Or did you by any chance add antiseize to the threads of the spark plugs? Too much antiseize, which is conductive, can find its way onto the electrodes and cause misfires.
 
You can check fault codes by cycling the ignition from off to on 3 times (do not start the engine). Any stored codes will show in odometer display.

You should also post your fault codes. Not all TPS codes indicate a sensor issue.
 
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The Autolite APP-985 spark plugs are not the reason for it missing now, that's a good choice for your model year. I'd be suspicious that perhaps the coil rail boots didn't make it all the way onto each spark plug correctly which has happened to me. Or did you by any chance add antiseize to the threads of the spark plugs? Too much antiseize, which is conductive, can find its way onto the electrodes and cause misfires.

This is it- it is hard to “feel” them seat-

Also on the 29 hp- don’t “Banks” on getting that much- but it will have enough power if geared correctly to do great on road and off. 04 is a good year for Rubicon- I’m sitting in one now. Stay with .035 for a crisp engine is my recommendation. Don’t pry against the small tip ever.

Mine was missing after a tune up once- I left the keys in it and my son took it.
 
I reseated the coil rail. It seemed like it was seated good. I reinstalled It and it definitely went on good and I torqued them down to 22ft lbs. It ran great for about three miles then it started missing again. The miss is intermittent. When it is missing and I give it more throttle, it stalls and almost dies. I limped down to Autozone and the code reader showed a faulty Exhaust Gas Valve (EGV) and a miss on number four cylinder. I bought a new plug and I’m going to pull it and check it out when I return home next week. . As I mentioned, I just bought the Jeep this week and I was running some Sea Foam thru it since it hasn’t been driven much lately. I’ll do some research and possibly clean the EGV or replace it. I’ll try and read the codes in the future like you suggested AjRagno. Thanks for the advice.
 
You don't need to use Autozone's clueless sales people to generate your trouble codes, your TJ has that ability built into its computer. Just quickly turn the ignition switch on-off-on three times within five seconds and then leave it in the on position. Give the diagnostics time to run, you'll start seeing any codes that are stored within several seconds. The last code shown, or if there are none, will always be 'donE'.
 
Will do! I meant EGR valve not EGV. There are a lot of videos on YouTube for addressing EGR valve changes on JK model Jeeps but none for a TJ.
 
You don't need to use Autozone's clueless sales people to generate your trouble codes, your TJ has that ability built into its computer. Just quickly turn the ignition switch on-off-on three times within five seconds and then leave it in the on position. Give the diagnostics time to run, you'll start seeing any codes that are stored within several seconds. The last code shown, or if there are none, will always be 'donE'.

Good to know. Thanks!
 
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Well I get the Buffoon of the week award! The code was showing a miss on cylinder number four. I just replaced the plugs so I didn’t think a new plug would be bad so I ordered a new coil rail. I decided to pick up a new plug and swap it out anyway. When I pulled the number four plug, I discovered that the gap was almost completely closed. I checked the gap before I installed the plugs and they were all perfect. I did drop that plug when I was installing them because the rubber insert in my 5/8 plug socket was worn out and wouldn’t hold the plug tight. I looked at it after I dropped it but I didn’t have my glasses on and didn’t notice that I bent the electrode almost completely closed. It runs perfect now with no check engine light! I just ordered a new set of plug sockets to prevent this happening again. Thanks for all the advice.