Wrangler misfire?

I have a 2011 Jeep Wrangler Sport, about a month ago I had a spark plug shoot out the head of my motor when I went to start it up. I was able to take it in where a Heli Coil kit was installed. After, it ran fine… Until I put it on the highway. it was doing fine for roughly 10 miles. I got up to 75 MPH and my check engine light begins to flash and my engine loses power significantly. i was able to get it towed but no codes saved to the check engine light relating to the misfire. went to the property later that night to start the jeep up, and no misfire was present, and it drove perfectly through the neighborhood/backroads. there was a single code for the rear passenger 02 sensor. Took it to the mechanic, i had them change all plugs, wires, coils, and new 02 sensor. when i picked it up, no check engine lights were on and it seamed to run fine. i gave it the big test and put it on the highway… and it made it up to 65MPH, check engine light began flashing, engine lost a lot of power. this time the check engine light stayed on the dash and ran code p0302. a misfire in cylinder 2. the same cylinder that had a spark plug shoot out a week prior.
my question is, I just tossed over $1000 on repairs for nothing to fix it. could the head itself be damaged? mechanic said the helicoil kit looked right and snug and it did drive fine with it under 60 mph. after the last misfire began on the highway day after tune up, Cylinder 2 now misfires at idle. it is going back to the mechanic in a couple days. been busy towing back and fourth between the shop and home all month and could use all the help i could get on diagnosing the problem. no cracks are visible, does not overheat, no leaks visible either. 3.8L 6 sp Manual

One theory, the thread repair procedure left some metal debris inside the cylinder, which is blocking or sticking something that shouldn’t be blocked or stuck.

Next theory, whatever caused the plug to be spat out the first time remains a problem. Plugs don’t normally shoot out of the engine like a rocket. Has to be caused by something, the spark igniting at the wrong time, carbon deposits on top of the piston or inside the cylinder head are causing the compression psi to be too high, or causing pre-ignition, etc. A crank angle sensor problem could cause this. If you believe that carbon deposits are an unlikely explanation, might be worth a gamble just to replace that part. I’d replace all the spark plugs at the same time on a flyer, paying careful att’n to what the threads and electrodes look like.

No experience with the heli-coil method, but fyi one of our experts here seems to prefer a product called a “time sert” for that application.

Thank you! I will definitely look into that sensor. I was for sure thinking the same thing when it came to what caused it to shoot out the first time. I was told over and over again its from aluminum threads wearing overtime. but when it shot out, it popped hard. and its not like I heard a loose spark plug ticking, it was very sudden and unexpected. Would a worn or damaged crank angle sensor throw a check engine code of its own? the only code I have on the dash now is P0302 which just says cylinder 2 misfire.

George is at least 1000 times smarter than me (but I did once, decades ago, work in a shop). The mechanic that changed the ignition parts had a good look at #2 spark plug which should have showed something if there is that bad of a problem with the Heli Coil. There was probably some malfunction at all speeds so the speed you were driving may be somewhat coincidental unless you were rapidly accelerating. If you think it’s an otherwise good engine, I like the crank sensor (or something else electrical) which should throw a code but you never know.

Sometimes yes, sometimes no. If there’s no signal from it at all, that would probably throw a code. An intermittent crank angle sensor might not. Sometimes the computer will detect a problem but not turn on the CEL immediately. In that case there could be a code pending. Suggest to ask that question to Google, might get some worthwhile ideas there.

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Took it back to the same mechanic that did the tune up. they took everything off to make sure it wasnt anything on their end. everything checked out good. they did take a look at the thread in cylinder 2 and it checked out good again. they said there wasnt any play with the spark plug itself and wasnt tightened too much/not enough. should be working properly. apon plugging everything back in and starting it up… it ran just fine. check engine light went away and the mechanics took a nice joy ride through town. everything seams fiixed. but i am not going to make the same issue three times in a row now and be stranded waiting for a tow again. i absoulty know that a misfire will occur again as soon as i put it on the highway. aint no way just unplugging and plugging wires and plugs again fixed the same cylinder misfire. what could cause the issue? is it more than likely computer related? i believe the computer was reset every time plugs were taken out and put back in. does this mean the computer “reset” and wont recognize theres a problem until the highway brings one out of it? the jeep misfired in idle before inspection today. any help is appreciated! thanks!

Possible, yes, b/c some problems won’t show up as a CEL or diagnostic code until they occur more than one time. I don’t think at this point you have any good alternatives rather than either (1) wait for it to happen again, then take it back to the shop or (2) take it to another shop for a pro-active workup and second opinion. Alternative (1) seems the best choice imo. On the positive side, it’s very possible whatever was causing the problem is now resolved.

You aren’t the only one to have this sort of car problem. I had a problem w/a VW Rabbit years ago, where it would completely stall while driving on the freeway for no apparent reason, after running perfectly for months. After waiting 60-90 minutes on the side of the freeway, it would start up and drive perfectly again. The shop had 3 or 4 goes at fixing the problem, before it was finally resolved. Turned out to be a combination of faulty fuel pump relay and a damaged relay plate.

Does the misfire continue after restarting the engine?

after it misfired last, it began when i was accelerating onto the highway. pulled over to idle, it remained misfiring. turned it off and back on, still misfires. just took it to the shop, they checked all their plugs, wires and coils that they installed, everything looked normal. put it back together, started it up and it runs fine. no check engine light either. drove fine through town, they did not put it on the highway. now im supposed to be picking the jeep up today but i already know when i put it on the highway itll misfire again. the check engine light must went away when the ecu reset when they pulled the plugs to check them. when the helicoil was first installed it ran fine at in town speeds. until i put it on the highway, the misfiring began. thats when i thought maybe wires or coils also went bad when the spark plug shot out. so i took it to the shop to do a complete tune up. its very compelling for me to believe the helicoil itself is an issue. mechanic doesnt see a problem with it, however something is not working with that cylinder when I accelerate to highway speeds. the confusion with that though is, why isnt the helicoil failing under 60mph? not causing any check engine light or misfire. it drove atleast 15 miles in town without issue but as soon as i get to the highway entrance ramp, it bout started flashing right after i went into 5th gear to get up to speed. nothing adds up to me anymore with this lol!

are you sure it is a Misfire now and not a hesitation coming from the tranny.

hmmm … well if the spark plugs threads into the helicoil ok, and produces a good seal (verified by a compression test), I can only think of three possibilities for it to cause a continuing problem

  1. Metal bits from the job remains inside the cylinder (as mentioned above). Seems unlikely. An experienced shop tech would almost certainly take proactive measures to prevent this from occurring.

  2. The HC is threaded in too far into the combustion chamber, and is interfering with a valve or the piston. Or interfering w/the spark electrode. Again, seems unlikely.

  3. . The portion of the HC inside the combustion chamber is getting hot and igniting the fuel charge in that cylinder before the spark occurs. Pre-ignition problem in other words. This also seems unlikely.

Has a compression test been done?

How far is the highway from the repair shop? Can’t you take someone from the shop for a ride to demonstrate the problem?