My check engine light came on about 2 weeks ago; pull the code and its P0302, misfire in the cylinder #2. My KJ has 28k miles on it, and i hadn't replaced the spark plugs yet, so i figured that was the problem. I take it to a local garage who i've had no problems with in the past, and they return it the same day with new plugs, and no CEL. A day later the CEL comes on again. Back to the shop it goes, where they check the compression, fuel system, clean the injectors and all is good again, for about a week. I reluctantly take it to the dealership; figuring service beyond what's been done will be covered under warranty. They have it for 2 days but claim they didn't see the CEL come on while it was there. They perform the BJ recall and give it back. All is fine for another week, and the CEL comes on again (same code). So i take it back to the dealership and they tell me the think there are still carbon deposits causing the CEL. They want to clean the injectors and fuel system again because they claim it looks like it had never been done and if that doesn't fix it remove and clean the cylinder heads (none of it covered by warranty). They also want to clean out the throttle body; I checked my throttle body last week when i re-oiled my K&N filter and it seemed ok at the time.

My first question is has anybody else had a carbon build up problem, especially in a KJ with relatively low mileage? Since i've gotten poor service from this dealership before, i'm more inclined to believe they are trying to shaft me. Is there anything i can ask to look at i'm at the dealership to confirm if they are telling me the truth and it was the first shop doing a poor job?

Thanks in advance

are you makin sure not to use too much oil?

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Admin note:
This account has been deactivated.

I did have some problems with carbon deposits in the engine of the Cessna 172Rs that I flew while I was in school and the procedure for fixing that is outlined last in this post, right before I hide from the lawyers.

Unleaded gasoline shouldn't ever leave carbon deposits in an engine that's operating normally...Does your engine run cool alot? If so, that would be the cause of the deposts.

Are you actually feeling any of the effects of this error code? Computers sometimes get confused, so I would place more faith in your instincts and feelings about the situation than the computer.

Now, I haven't had a chance to tinker with our KJ yet (brandy new), but first solution possibility would be to throw in a bottle of injector cleaner with your next fillup. If that doesn't work, run about 2-5 gallons of Shell Premium (it has cleaning agents in it) through the engine. The high octane will burn slightly hotter, and it is also a stronger solvent than regular. The higher temperature MIGHT be enough to remove the carbon deposits, assuming that they're actually there.

If this fails, and you are in fact feeling/hearing a knock in the engine (idle is the best time to tell, if it's idling rough or higher than normal then something is wrong), then see if there is a way to lean the mixture on the engine almost to the stalling point for a few seconds at a time. This will drastically raise the cylinder temps, which WILL burn the carbon from the heads, plugs, and injectors.

-I accept no legal responibility for anything that you try doing to your vehicle based on this post, by trying anything I suggested, you are doing it of your own free will and I cannot be held responsible, no matter how much you f*cked anything up. Again: ZERO legal liability from this post.-

It's sad that I felt the need to write that.

positive...very light coats until the cone turns red. I think its the first thing the guy at Autozone told me when i bought the recharger kit, don't over oil. If I hadn't gotten the error code 2 times before i oiled the cone, i would suspect me first.

Just so i know in the future, what error codes would be caused by over oiling the filter? The O2 sensor is in the tube, wouldn't that be affected also?

No worries about the disclaimer, i understand.


The temp gauge needle gets to half way and stays there...never above, rarely below. 90% of my trips are 30+ miles. Don't know how far that goes to addressing that possibility.


That's just it, i haven't noticed any changes at all other than the light. When i took it in the second time, they told me it was barely misfiring, a couple times a minute (don't know if that's a lot or not, just what i was told). No problems starting up, idles fine, no knocking or changes in mpg and accelerates fine. I add a bottle of stp fuel system cleaner with every oil change (amsoil every 6k). I think that's the most frustrating part..this is the first new car i've owned and do everything to the letter then some. Right now i'm leaning toward picking up the jeep from the dealership then cleaning the throttle body again, maybe run a small amount of premium thru to see if it helps. If nothing else its one less thing somebody will charge me for. Leaning out the fuel mixture is beyond by abilities, so I'm hoping the first two do the trick.

you only have 28k miles on the kj and its not covered under warranty???

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Drop what your doin, and go drive your jeep!!!!
03 Jeep Liberty Limited
4X4

Take it to a different dealer and have them fix it under warranty... that is rediculous that a dealer wants to charge you for somthing that should be covered under the 3/36 bumper to bumper.

Just to be safe though - throw a paper filter in the airbox before you take it in.

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02 Liberty Limited
Silver Outside & Taupe Inside
Heated Seats, Sunroof & Infinity speakers
USA Spec I-Pod adaptor, Mopar Sub, Garmin GPS
Tow Package, Select-Trac
Rock Rails, Tow Hooks

Didn't anyone check the ignition wires? If nothing else, try switching wire #2 with another and see if the error code changes.

I would do something like nova suggests to determin if it is the ignition coil. But at less than 36K the dealer should be doing all the for free. I'd really be trying a different dealer if it was me.

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Brian, Blue KJ in PA
LOST#99, Mid-Atlantic LOST
Blue 2003 KJ Sport

RL Super Skinks

I agree.

Thanks guys for all the responses.

I agree, i'm picking up the jeep this afternoon...i've called one other dealer so far and they told me it was "part of routine maintenance, like an oil change and not a warranty service." I thanked the rep for his time and moved on. There are two or three other dealerships within an hour's drive, i'm about to call them now.

The local shop checked them the second time it was in, and they checked out ok.

Thats BS I would tell them that the CEL is not REGULAR maintenance!!! And what ever they have to do to fix it whether it be something that is usually regular maintenance becomes warranty work when that nice little light on the dash comes on!

_________________
Drop what your doin, and go drive your jeep!!!!
03 Jeep Liberty Limited
4X4

Just to update the dealership scorecard, Warranty work: 0 Maintenance i pay for: 3. Quoting the last dealership i called: "If a fuel injector flush is necessary, its because of a foreign objects getting into the engine, thru the fuel for example. Therefore its not a warranty item, its a service item."

I have one or two more i can call, but i'm sensing a pattern developing...here's a bigger question tho, what could have causes carbon build up in the first place? This is the first time i've had this problem with a car. Almost all my driving is highway driving, which seems easier on an engine than lots of stop and go. Like i said before, i've used the fuel cleaner additives regularly, changed the oil regularly with synthetic, kept the filter oiled and throttle body clean. Am i missing something? The stock airbox was replaced over a year ago with a K&N FIPK and the exhaust with the mopar dual output exhaust. I was set to order the fastman throttle body but the jeep was in the shop during the time i had off over the holidays.

When the CEL comes back on(or if it's already on) take to another dealer that you haven't talked to and have them fix it under warrenty.Any item or service that results from the CEL being on should be covered under the 36/36000 warrenty.The K&N could be a deal breaker at most dealers though.

i gotta a question, its relevant, can you over oil an air filter??? and if so could that be the cause of his problem???

_________________
Drop what your doin, and go drive your jeep!!!!
03 Jeep Liberty Limited
4X4

Yes and it's possible

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02 Liberty Limited
Silver Outside & Taupe Inside
Heated Seats, Sunroof & Infinity speakers
USA Spec I-Pod adaptor, Mopar Sub, Garmin GPS
Tow Package, Select-Trac
Rock Rails, Tow Hooks

Be sure when you take it in that you don't mention anything other than the check engine light came on. Tell them you recently put in new plugs and an air filter as routine maintenance. Do not tell them you have spoken with other dealers or even mention deposits. They want their gravy (easy, quick work that pays well) and a BG flush is just that, gravy. If you do have carbon deposits, there are several remedies that will take care if it very quickly. I like Berrymans Chemtool and Seafoam, of coarse there is the old ATF sucked through the PCV valve trick as well. It will smoke the neighborhood up pretty good, but it works very well. I suspect that carbon is not the problem. Could you have gotten a tank of gas with some moisture in it? I would also make sure that they hook up an O-Scope or what ever they use now and see which cylinder is misfiring and check all ignition components for that cylinder. Let us know how this turns out.

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'03 Sport
Grand Cherokee TCM, Skids, Superwinch EPi 9.0 in cradle mount with 125' 5/16 Viking Trail Line, Mopar Rock Rails, Trac-Loc Diff, Frankenlift in front and Skyjacker/JBA springs out back, Monroe Reflex Shocks in rear, JBA Gen 4.5 Upper Control Arms, Moog LBJ's, 245/75/16 Goodyear Wrangler Duratracs.

I agree, don't tell the other dealer you take it to about the carbon deposits. Im beginning to also think the carbon is not the problem from all the work thats been done to it, and since there are a lot more reasons for a cylinder to misfire.

_________________
Drop what your doin, and go drive your jeep!!!!
03 Jeep Liberty Limited
4X4

yea it's definitely possible to over oil the filter which is why i was careful about it. But the engine light came on the first two times with code P0302 before i oiled the filter (really cone). And that was the first time the cone has been recharged (it has less than 20k on it). From searching the net, i've found plenty stuff on over oiling a filter; but the damage in every case has been to the MAF sensor. Neither place i've taken the jeep to has mentioned the MAF sensor as a problem. If the dealer wanted to point the finger at me that would be the easiest way, my non-mopar mod.

I hope it isn't more than carbon deposits, but it does seem like a possibility since the first shop has always done good work for me and friends. I asked them not to do anything more than change the plugs, check ignition wires, etc. They did the flush on the second visit but again nothing more at my request because i figured everything else would be covered under warranty. I guess there moisture could have gotten in the tank, but I can't think of what would have changed in my routine to cause that other than sometimes sh*t happens. Taking it to one of the dealers i have not called yet seems to be the best option, and there are a couple in the area i haven't spoken to. Would one dealer be able to see what another dealer did, or in this case didn't do? When i picked up the jeep, i got an invoice even tho they didn't charge me. On the invoice was their diagnosis and a note that i picked up the jeep w/o the recommended service being performed.