cylinder misfire, multiple codes. -
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Unread 09-30-2012, 12:24 AM   #1
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2005 LJ Wrangler 
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cylinder misfire, multiple codes.

1. Sorry for the lengthy post, I know most of these things have been discussed before but alas, here I am.
2.I troubleshoot Avionics system on fighter aircraft for a living and consider myself relatively inclined mechanically so try not to insult my intelligence TOO much
3.I HATE paying a shop to do something that I could do myself.....BUT

this has been an ongoing issue for months and now seems to be coming to a point where I'm at a bit of a loss and looking for some advice before I gut my wallet at a dealership or a shop..
quick rundown:
-about 6 months ago had o2 sensor issues, replaced all 4 sensors with bosch units (I know..), no fix. ended up being the aft mini-cat totally gutted. So all new cats now.
-Then had a bank 2 sensor 1 code, put the original stock sensor back in, fixed for a few weeks, then the P0152 came back along with a P0300 (multiple misfire). Took apart the TB and fuel injectors and cleaned everything quite well including all sensors on the TB iteself (IAC/MAP/TPS) A LOT of build up in there so it looked promising. Put back together and then had some low rpm stumbling (wasn't there before). Rechecked the plugs (looked good, they were recently replaced-autolights) and put some good cleaner through the tank. I read the Coil pack and Fuel filter/pump are lifetime items so I'm ruling those out for now..
-Stumbling never went away, but ran GREAT above 1500 rpm.
-Then got P0300, P0303, and P0152. Common denominator seems to be either fuel injectors or the 02 sensor. Have been trying to find schematics to shoot all assoc. sensors but the info out there is lacking.
-Did a compression test and the 3rd cylinder was ~160 compared to ~180 for the rest, then a wet test on all and got about 20 psi increase on all respectively, so now I'm thinking piston rings. So for S&G's I put a can of restore in the oil to see if I could get any improvement.
-Just checked codes again and I'm now getting P0300, P0303, P305, P0627, and P0152... the 627 is pointing to fuel control relay circuit. Not sure how as I haven't messed with the tank or assoc parts, only thing was the actual relay when doing the comp test, but that is seated properly. It's running worse now at all rpm's, actually feels like its missing on a cylinder or two

SO, I'm just trying to figure out if this is just a snowball ****show of issues or if there is possibly one good root cause of all of this. Aside from putting yet another rear upstream o2 sensor or fuel injectors idk.

P.S. I've done about as much homework as one could online and via the haynes manual...I'm just trying to minimize the cost of replacing everything twice, or god forbid a complete engine overhaul. I feel like I already know what I'm going to get for responses but at this point it can't hurt to ask. Thanks in advance


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Unread 09-30-2012, 01:27 PM   #2
Tks 4 the upgrade Blaine
Rubi4MyMrs's Avatar
2005 LJ Wrangler 
Join Date: Mar 2011
Location: Trails of, Nevada
Posts: 2,639
The Haynes manuals leave a lot to be desired. Get an FSM. Since the misfires are on #3 & #5 you dealing with both banks of the exhaust so I don’t see the O2 sensor as likely related to the misfire. The misfire might be the cause of that code though. You might check the injector spray pattern & quantity of those 2 compared to one of the others. You can also switch the injectors & see if the misfire follows to other cylinders. As for the P0627 I would do a reset & see if that returns.

Not perfect for ‘05s but this link gets FSMs but for ’05 you need to pick TJ Unlimited & I think that is actually for ’04 (comparing it to my ’05) but still much better then Haynes.

See online read only FSMs here:
You may have to go to the bottom of the page & pick Jeep Resources & online manuals if it directs you to home page rather than the knowledge base.
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Unread 09-30-2012, 04:38 PM   #3
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2006 TJ Wrangler 
Join Date: Sep 2009
Location: Cypress Creek, Louisiana
Posts: 82 Go read this. Mine started with the codes. it was this and my number 5 cylinder is dead. have to pull motor. ethier camshaft lobe is wore off or lifter is wore out. they had a recall in 05 for defective camshaft and lifters
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Unread 09-30-2012, 04:52 PM   #4
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Mudmachine, I skimmed the post, but there was 100 pages. But you're referring to the OPDA issue? I'm aware of those going bad... Although It might be something to look into. frankly I've only pulled it apart once last year after learning of it being prone to wear, and didn't seem to have any issues. Totally spaced it though, I'll take a look. Thanks.

Last edited by gomar83; 09-30-2012 at 05:03 PM..
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Unread 09-30-2012, 04:58 PM   #5
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Thanks for the info Rubi4.. I was actually today just messing with the injectors, swapped them out for the Neon 2.4 4-port type that I've heard about...figured at this point it couldn't hurt to try and if there is an improvement in the process why not. I disco'd the batt before the job and reset the codes, started up and seemed to improve slightly. The codes cleared but probably won't take long for something to come back. It also still sounds like a misfire throughout the rpm band. Also on the way to the junkyard (seems to be a pattern) once it's driven for more than 5-10 mins everything kindof smooths out, as if the misfire and stumbling go away completely. Odd...

Thanks for the input guys.

I hope mudmachine isn't right haha.
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Unread 10-17-2012, 11:20 PM   #6
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update: In case anyone cares, I found what seems to be a fix.

I changed the coil rail and put new plugs in Autolite app985, and replaced the aft/upper o2 sensor with a Denso unit...Runs like a champ. Couldn't say for sure what fixed it but I'm leaning toward either the rail or plugs.

No stumble at any RPM, and the check engine light went out after about 4-5 cycles.
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Unread 10-18-2012, 07:20 PM   #7
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2004 LJ Wrangler 
Join Date: Dec 2011
Location: Norwalk, CT
Posts: 684
Glad you got it fixed, but this is a great point. Pay the money for the quality parts the first time or be prepared to buy them twice. Happened to me too after I had a misfire in cylinder 1, ended up being a burned exhaust valve and I just replace the whole head, but in trying to figure it out, I replaced the TPS with a autozone crappy one, started giving me a low voltage at the TPS, when I looked at it, the damn thing fell apart in my hand! Ended up going to the dealer for a quality made in america part..issue solved. Hope you mis-fire days are behind you though!!
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