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post #1 of 16 Old 07-26-2015, 11:47 AM Thread Starter
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Help with engine miss.

I need to see if anybody can help with an engine miss I've been having. It's like a slight stumble every 4-5 seconds. It's only ever thrown a check engine light twice and it was the one for "misfire cylinder #3" (can't remember the code right now but it was the same both times). The code went away on it's own after a day or so.

I changed the plugs and plug wires about a year ago (~15k miles). I used the OEM plugs and a set of advance auto wires. I figured it was the cheap wires so I just put on a set of AC delcos and it's still there. The plugs look like new still so I haven't bothered with them. The EGR valve was replaced about a year and half ago due to it going bad and throwing a CEL. I've replaced the PCV valve (even though it was only a year and a half old too) and installed a new air filter. I've removed and cleaned the throttle body along with spraying carb cleaner along the vacuum lines to see if one was leaking. It's not using any coolant, blowing white smoke and no coolant in the oil so I'm pretty sure it's not a head gasket.

Can anybody please help me in figuring out what it could be because I'm at a dead end here. Could the ignition box be bad but not completely fail, just miss every now and then?? Oh and it's an 07 JK 3.8 automatic tranny with 103,000 miles on it. I've always performed the maintenance on it since I got it at 50,000 miles.

Also wanted to add that my gas mileage (13.5-15mpg) is the same and it seems to run fine under throttle and has the same (lack of) power it's always had since I put 35's on it. LOL So I doubt it's a clogged cat. It also has no exhaust leaks that I can hear (I've replaced the drivers side manifold twice now).

I'd greatly appreciate any help. Thank you.

Mine: 07 Unlimited Rubicon. Red rock crystal. RC 2.5" spacer lift. 35x12.50 mtr/k's mounted on 15x8" black mb72 wheels. Riddler diffs covers, PSC evap skid. Sleeved, gusseted and skidded front axle.

Hers: 05 WK limited 4.7, Midnight blue pearlcoat.
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post #2 of 16 Old 07-26-2015, 12:13 PM
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Since you have already replaced the plugs and the wires, the only thing left is the coil pack. An intermittent miss is hard to diagnose. But most likely you need a coil pack.
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post #3 of 16 Old 07-26-2015, 12:41 PM
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Agree with the coil pack check. I had a similar problem on another vehicle. I had replaced the plugs and plug wires 6 months prior. With the help of a friend we started my engine up at night in the pitch black and observed the engine with the hood up. Two of the wires were arcing to the engine block and an engine bracket. Sparks show up really well. good luck.

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post #4 of 16 Old 07-26-2015, 01:05 PM Thread Starter
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Thank you guys. I think I'm gonna replace the coil pack. They're not too expensive anyway. I just always thought that when they went they just completely died.
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post #5 of 16 Old 07-26-2015, 05:15 PM Thread Starter
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Well that wasn't it. I'm completely lost on what it could be. I picked up a new coil pack and put on and it's still stumbling. It's almost like a vacuum leak but the idle never picked up as I sprayed the vacuum lines like it would if one was leaking.
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post #6 of 16 Old 07-27-2015, 09:03 AM
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So i'll throw my .02 out there, sense you have replaced you manifolds wouldn't hurt to go back and check your bolts where the manifolds meet the CAT, Reason is a little while ago I had a little miss couldn't figure it out. I decided to look over few other things and found the two bolts were loose. tightened them up and it runs just fine now. Like you said above, no exhaust leaks...So may or may not be that, just my .02

Good lucky figuring it out!

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post #7 of 16 Old 07-27-2015, 11:33 AM Thread Starter
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I'll go give it a check. I don't hear any leaks though but maybe it's just small enough.

Mine: 07 Unlimited Rubicon. Red rock crystal. RC 2.5" spacer lift. 35x12.50 mtr/k's mounted on 15x8" black mb72 wheels. Riddler diffs covers, PSC evap skid. Sleeved, gusseted and skidded front axle.

Hers: 05 WK limited 4.7, Midnight blue pearlcoat.
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post #8 of 16 Old 07-28-2015, 08:05 PM Thread Starter
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Note the bolts are good and tight.
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post #9 of 16 Old 07-28-2015, 08:15 PM
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So the stumble (felt miss or running issue) is consistent, but the misfire code is not, is that right?
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post #10 of 16 Old 07-28-2015, 08:23 PM
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It also could be a injector failing. If all else fails swap things around to see if it follows. Saves on buying parts you dont need.

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post #11 of 16 Old 07-28-2015, 10:49 PM
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i'll back up RubiCajun and mention that twice the OEM ignition wires have developed the tiniest of holes in the grey sleeve where the plug-caps reside & troubleshooting a misfire that would ensue on that cylinder was finally only possible because I heard the arc popping + could see the blue arc tucked way around the back of the number 5 and number 3 ports thru to the engine block. I got plug socks and re-routed the wires from around back to over the engine valve-cover with 1800 degree heat-shield wrap and a drag racing flame /heat tube from Heat Tech or something from Summit to wrap over that and no problem since. I think the heat over the driver side exhaust mani accelerates wire breakdown ( if that's possible) and this has not returned ....check for sparks , look at injectors, add dielectric grease to the wires , et. all.....hope this helps....sorry, i type a lot....


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post #12 of 16 Old 07-30-2015, 01:56 PM Thread Starter
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Quote:
Originally Posted by BigTB View Post
So the stumble (felt miss or running issue) is consistent, but the misfire code is not, is that right?
Yeah it has a constant miss/stumble every few seconds at idle but over the last couple months of it doing it it only threw a code twice. Both times it was a cylinder #3 misfire. Both times it went away on it's own too.

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It also could be a injector failing. If all else fails swap things around to see if it follows. Saves on buying parts you dont need.
That's a good idea! I never even considered an injector going bad.

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Originally Posted by j3ff3ry_j33p View Post
i'll back up RubiCajun and mention that twice the OEM ignition wires have developed the tiniest of holes in the grey sleeve where the plug-caps reside & troubleshooting a misfire that would ensue on that cylinder was finally only possible because I heard the arc popping + could see the blue arc tucked way around the back of the number 5 and number 3 ports thru to the engine block. I got plug socks and re-routed the wires from around back to over the engine valve-cover with 1800 degree heat-shield wrap and a drag racing flame /heat tube from Heat Tech or something from Summit to wrap over that and no problem since. I think the heat over the driver side exhaust mani accelerates wire breakdown ( if that's possible) and this has not returned ....check for sparks , look at injectors, add dielectric grease to the wires , et. all.....hope this helps....sorry, i type a lot....
I just put brand new AC Delco wires on it and it didn't help it. I'll check back where they run behind the intake though and see if they're arcing. I've also though of running them up and over the intake just to simplify it. Didn't know if there'd be a heat or clearance issue or not though. Oh and I always use dielectric grease at both ends of the plug wires.

Mine: 07 Unlimited Rubicon. Red rock crystal. RC 2.5" spacer lift. 35x12.50 mtr/k's mounted on 15x8" black mb72 wheels. Riddler diffs covers, PSC evap skid. Sleeved, gusseted and skidded front axle.

Hers: 05 WK limited 4.7, Midnight blue pearlcoat.

Last edited by pajkrubi; 07-30-2015 at 02:00 PM.
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post #13 of 16 Old 07-30-2015, 04:23 PM
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don't assume recently replaced plug wires are necessarily good. pin holes as was already stated as well as broken connectors from folks pushing them on and pulling them off could mess things up.

If you can get the rig on a scope, you'll see right away if you have a bad wire or coil. Short of that, you can do I the old fashioned way by testing each wire with a grounded spark plug on the end (not installed). I used to have this thing from the mac tool guy that had an alligator clip soldered to a surface gap spark plug thingy. I even bought a hammered old scope at the time to keep in my stall just to check for bad plug wires (and bad plugs for that matter).

If the injector is failing electrically, that should show up in the form of a code. If it is dirty, you might be able to clean out by running something like BG44K fuel system cleaner. It's gnarly shit so you'll want to do it just before an oil change (run the whole tank of gas through first).

then there is ye olde compression and leakdown testing, with special attention on #3 as you mentioned.
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post #14 of 16 Old 08-02-2015, 08:55 PM Thread Starter
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Well after tons of head scratching and replacing parts it turns out it was the damn plugs! They looked fine but after swapping out another set of champion double platinum oem plugs it runs great again. I'd always heard that platinum plugs were factory gapped and not to regap them because you could damage the platinum specks so I just threw the last set in. After checking my new ones I had to adjust the gap to the factory .050" on four of the six! And checking my old ones most were up around .060" or bigger! So the plus were probably good, just too much gap and the spark was not lighting. Thank you everybody for all the tips and help though. At least my jeep has a lot of new parts now. Lol and thankfully a lot of stuff for this jeep is fairly cheap compared to some vehicles parts. I even got six reman'ed injectors and swapped out. Not too bad of a job actually. I also put new upper plenum gaskets in since I was in there and they were cheap. It should run like a champ now! Lol if anybody ever does need injectors though check out injector warehouse. I got all six with free shipping for $148!! And they were at my house in two days. Well thanks again everybody!

I'm so glad I finally got this figured out because I was getting really worried because the topless for tatas ride is next weekend and I'm a guide. Wasn't sure if I was gonna have to back out at the last minute. That would have killed me because this is my third year guiding and the wife and I LOVE it.
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post #15 of 16 Old 08-02-2015, 10:22 PM
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Quote:
Originally Posted by pajkrubi View Post
Well after tons of head scratching and replacing parts it turns out it was the damn plugs! They looked fine but after swapping out another set of champion double platinum oem plugs it runs great again. I'd always heard that platinum plugs were factory gapped and not to regap them because you could damage the platinum specks so I just threw the last set in. After checking my new ones I had to adjust the gap to the factory .050" on four of the six! And checking my old ones most were up around .060" or bigger! So the plus were probably good, just too much gap and the spark was not lighting. Thank you everybody for all the tips and help though. At least my jeep has a lot of new parts now. Lol and thankfully a lot of stuff for this jeep is fairly cheap compared to some vehicles parts. I even got six reman'ed injectors and swapped out. Not too bad of a job actually. I also put new upper plenum gaskets in since I was in there and they were cheap. It should run like a champ now! Lol if anybody ever does need injectors though check out injector warehouse. I got all six with free shipping for $148!! And they were at my house in two days. Well thanks again everybody!

I'm so glad I finally got this figured out because I was getting really worried because the topless for tatas ride is next weekend and I'm a guide. Wasn't sure if I was gonna have to back out at the last minute. That would have killed me because this is my third year guiding and the wife and I LOVE it.

are those OEM injectors? That is a good price if so. I guess I could head over to the web site and look, derp....
glad you got it corrected; lesson learned = always gap your plugs ( I had never heard not to gap plats yourself...not enough bending in a gap increment to break anything, if grasped firmly....) or at the very least check this supposed "factory gap" info....I couldn't install a set of plugs without checking the gap, tbh. And White143JKUR is totally correct on assuming wires to be good even after install of new; I was using one of those el cheapo metal spark plug boot remover tools from dollar bin of O'Reily's and couldn't figure out till third wire that IT was putting the pinhole in the boot each grasp ( arg) and learned it doesn't take much to tear those things. Good to go on the dialectic grease and ya got new injectors and plugs. cool!
Well worked out, man. Jeep On


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post #16 of 16 Old 08-03-2015, 08:33 AM Thread Starter
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are those OEM injectors? That is a good price if so. I guess I could head over to the web site and look, derp....
glad you got it corrected; lesson learned = always gap your plugs ( I had never heard not to gap plats yourself...not enough bending in a gap increment to break anything, if grasped firmly....) or at the very least check this supposed "factory gap" info....I couldn't install a set of plugs without checking the gap, tbh. And White143JKUR is totally correct on assuming wires to be good even after install of new; I was using one of those el cheapo metal spark plug boot remover tools from dollar bin of O'Reily's and couldn't figure out till third wire that IT was putting the pinhole in the boot each grasp ( arg) and learned it doesn't take much to tear those things. Good to go on the dialectic grease and ya got new injectors and plugs. cool!
Well worked out, man. Jeep On
I'm pretty sure they're OEM injectors because they looked exactly like my oem ones and I have to return mine to be remanufactured.

Yeah I usually check the gap before installing anyway but for whatever reason I didn't on this last set. I'm guessing because they were the double platinums.

Mine: 07 Unlimited Rubicon. Red rock crystal. RC 2.5" spacer lift. 35x12.50 mtr/k's mounted on 15x8" black mb72 wheels. Riddler diffs covers, PSC evap skid. Sleeved, gusseted and skidded front axle.

Hers: 05 WK limited 4.7, Midnight blue pearlcoat.
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