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Old 03-27-2014, 09:26 AM   #1
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Rough Idle and #2 Misfire

2006 LJ Rubicon. 4.0. Auto. 86k miles

For the last couple of months I have been battling a rough idle and a #2 misfire (code p0302). I have done plenty of searches, and I have tried many things, but it is still an issue.

Things I have tried to rectify the issue:

New exhaust (cats and cat-back)
New 02 sensors
New DP plugs
New TPS
New air filter
Cleaned throttle body and IAC
Checked injector o-rings
Checked hoses for leaks

Things I am doing today:

Stopping by AutoZone to get the code read (been using the "trick" to read the codes)to make sure nothing else is popping up.
Going to swap out the #2 injector with another one to see if the misfire changes.
Check plug on #2 (even though this was happening before the new plugs).

The problem seems to happen when I am doing a lot of errands in one day. A lot of short trips with a a lot of turning the engine on and off. The idle will get rougher and rougher and eventually a misfire will happen on #2.

Besides what I plan on doing today, is there anything else I should check for or any ideas on what is causing the issue?

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Old 03-27-2014, 09:48 AM   #2
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Coil rail!!! I'd seriously look into that coil rail if you're getting those misfire codes.

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Old 03-27-2014, 09:50 AM   #3
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Pretty sure I heard an exhaust leak this morning on my way to work. I will check that tonight as well.

Any way to check coil rail without replacing it?
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Old 03-27-2014, 10:06 AM   #4
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Not sure how to check that coil rail. I've always just replaced it if I suspected it, not to mention based on what you've already replaced it seems like it's all that's left except the injectors swap you mentioned.

I'm certain there are some more experience tech's on here that might know a few tricks on checking it.
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Old 03-27-2014, 03:05 PM   #5
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I have the same issue. I replace the plugs about 1,000 miles ago so a bad plug is the first thing I am going to check.
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Old 03-27-2014, 03:44 PM   #6
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I am going to try some things tonight and I will post results when I get them.
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Old 03-27-2014, 07:55 PM   #7
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Replaced the coil rail, switched #2 and #4 plugs, and switched #2 and #3 injectors. Tightened down loose exhaust and fixed the leak. So far so good, but since I had to disconnect the battery, only time will tell if it worked or not. Hopefully it did, but if it didn't hopefully it shows me if the plug was bad or if the injector was bad, and not something internal in #2.

I do have the Mopar Added Care Plus warranty though, so if something internal, it should be covered.
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Old 03-27-2014, 08:30 PM   #8
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Sounds like a well thought out plan of attack

You even avoided any 2 and 5 swap which is good as those two coils fire together

If it stays 2 it could be a problem with the harness to injector 2
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Old 03-27-2014, 09:16 PM   #9
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I hope what you did in post #7 takes care of the problem but if not, exactly what brand & model spark plugs did you install? Due to the coil rail ignition design, 2003 and newer 4.0L engines are very (!) fussy about the spark plug technology they will run properly with.
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Old 03-27-2014, 10:00 PM   #10
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Autolite app985
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Old 03-27-2014, 11:15 PM   #11
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Autolite app985
Good choice. Providing they're in good condition, they're not the problem.
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Old 03-28-2014, 11:51 AM   #12
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Quote:
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Good choice. Providing they're in good condition, they're not the problem.
I used Bosch OE Platinums. Was that a bad choice?
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Old 03-28-2014, 12:19 PM   #13
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Maybe, maybe not. If they have the platinum coating on both sides of the gap they are fine. If on just one side of the gap, no. This is applicable to 2003 and newer 4.0 engines.
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Old 03-28-2014, 12:53 PM   #14
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Thanks. I guess I will just toss them. Can you recommend a good replacement.

2003 Wrangler X 4.0L with 122k miles on it.
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Old 03-28-2014, 12:59 PM   #15
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Autolite APP985 (not AP985) or Champion 7034 will both perform well for 100k miles. Autolite's XP985 iridium tipped plug will get you somewhere close to 200k miles.
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Old 03-28-2014, 03:23 PM   #16
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Thanks Jerry.
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Old 03-28-2014, 04:42 PM   #17
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Did a lot of running around today and got an oil change while I was out. So far so good, no new CELs but it usually takes a few weeks for one to pop up again if it is going to.

The idle is still a little rough, but no where near as bad as it was. The exhaust however is now banging on the side of the tranny (the catalytic converter). I tightened it up at the exhaust manifold, but for some reason the rest of it seems loose, especially the cat-back. The hangers don't seem to have shifted, but they don't seem to be as "stiff" as they were a few months back.

I will post back in a few weeks and let you know if the CEL comes back and if so, what the cause is.
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Old 03-28-2014, 05:51 PM   #18
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There is a hanger that comes off the transmission mount above the tcase skid too I didn't know was there for a long time.
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Old 03-29-2014, 06:40 PM   #19
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I switched the #1 and #2 plug, cleared codes and the #2 misfire came back so the plug was ok. I replaced the coil rail and the camshaft position sensor. Seems to be OK now.
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Old 03-29-2014, 09:21 PM   #20
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Too soon. Looks like it is still misfiring. New Camshaft position sensor, new coil rail and new plugs. Still number 2 misfire. I guess all that is left is crank sensor or injector. Any recommendations?
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Old 03-29-2014, 10:15 PM   #21
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Could be intermittent connection in harness to injector 2. You have ruled out coil rail and injectors and plugs by swaps. Not a harness problem to coil as same wires fire 2 and five and miss is only in 2

The injector harness to a single injector gets a constant plus 12 when key is in on position and a pulsed negative from PCM
If you make up a little harness with a injector connector at one end and one wire to fused positive at battery and other jumped to wire to injector 2 attached right where it leaves the PCM you will have a factory harness bypass and if that rids the intermittent miss you know it is that harness then just gotta trace it down. Cannot think of any other intermittent issue you have not addressed
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Old 03-29-2014, 11:18 PM   #22
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Check out the Chrysler service bulletin number 18-031-03. Search it on the forum here, see if the symptoms are similar. Seems to have helped on my 2004 TJ.
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Old 03-30-2014, 10:40 AM   #23
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Thanks for the TSB info. It seems like I jumped the gun. My son drove the jeep about 30 miles and the check engine light is back on. This time P0303. Misfire is now on cylinder #3. Where I switched the original spark plug from misfiring #2. Misfire followed the plug. In post #19 I said I switched plug #1 and #2. That was my plan but I switched #2 and #3 because it was more accessible. I think this confirms the plug.
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Old 03-31-2014, 09:26 AM   #24
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It was the plug.
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Old 03-31-2014, 09:45 AM   #25
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So far mine is still running great. I think the rattle I'm hearing might be my tire carrier. It only happens on bad bumps and is coming from the back somewhere.

After every cel fix it would take a few weeks to come back, so only time will tell.
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Old 04-05-2014, 10:28 AM   #26
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Similar problem

I switched to Autolite APP985 plugs sometime last year to improve performance and longer plug life in my 2005 4.0L. Several months later it was throwing codes for cylinder 1 and 2 and multiple cylinders and I could tell it was misfiring. I swapped plugs around to no avail. The only other thing I did was run Seafoam in tank and through throttle body a couple of times in case it was carbon build-up on the valves. I reset the OBDII the first time and the codes came back and the second time it did not clear the code.

So I swapped to NGK ZFR5N3459 and it wouldn't even run (started, ran horrible and would kill the engine). I simply took the coil rail off and reset it and it runs perfectly and no codes for a month now.

This is "for the record". I wanted to run the platinum plugs, but unless it gives me a significant mpg bump I don't mind changing spark plugs every 15K miles or so. Only took about 30 minutes anyway - if you get the rail on perfectly...

Chetzki
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Old 04-18-2014, 08:07 PM   #27
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Today it started running rough again. No cel yet, but I'm going to go and tighten down all the exhaust bolts and see what that does if anything. I'm hoping it's just something loose. It accelerates fine and does not feel like it will stall, but when sitting in park or waiting at a red light it is really starting to shake and feel rough again.
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Old 04-21-2014, 10:06 AM   #28
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Quote:
Originally Posted by Duck Vader View Post
Today it started running rough again. No cel yet, but I'm going to go and tighten down all the exhaust bolts and see what that does if anything. I'm hoping it's just something loose. It accelerates fine and does not feel like it will stall, but when sitting in park or waiting at a red light it is really starting to shake and feel rough again.
Best of luck! I can imagine how frustrating. Let us know if that resolves.
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Old 04-24-2014, 01:33 PM   #29
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I ended up replacing the manifold intake/exhaust gasket. I was just going to tighten them all down, but since I had to take off the cats just to get to the damn bolts I said f-it. Might as well just replace the gasket with a new one and use some good sealer. The top bolts were easy to take off, but the bottom ones were on REALLY tight. Thought I was going to break some, but it all went smoothly. The gasket that was on there originally had no sealant and was not very good.

It now runs a lot better and a lot quieter.

I do have a new issue though. The flange around the 3rd cat (the one closest to the muffler) is rubbing on the transmission mount and is driving me nuts. I was going to try and get under there tomorrow and see about bending the edge, but I don't want to run the cat. Is there any type of rubber or anything I can put between the two that is high heat tolerant so when it does rub it doesn't drive me insane?
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Old 04-24-2014, 01:57 PM   #30
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How about a slither of radiator hose (I'm sure a local shop might have some on hand from a recently replaced hose) and place it in between the two. Maybe a steel hose clamp to secure it?
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I ended up replacing the manifold intake/exhaust gasket. I was just going to tighten them all down, but since I had to take off the cats just to get to the damn bolts I said f-it. Might as well just replace the gasket with a new one and use some good sealer. The top bolts were easy to take off, but the bottom ones were on REALLY tight. Thought I was going to break some, but it all went smoothly. The gasket that was on there originally had no sealant and was not very good.

It now runs a lot better and a lot quieter.

I do have a new issue though. The flange around the 3rd cat (the one closest to the muffler) is rubbing on the transmission mount and is driving me nuts. I was going to try and get under there tomorrow and see about bending the edge, but I don't want to run the cat. Is there any type of rubber or anything I can put between the two that is high heat tolerant so when it does rub it doesn't drive me insane?

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