[gilliganspl]

I had my MIL go on over the weekend, but I didnt have any noticeable symptoms. I took it to get read at autozone and they came up with the 0303 cylinder 3 misfire. I have taken it to get read in the past and after they read the code it usually makes the light go off, however this time it did not. I took it to another autozone a couple of days later because sometimes the people there really have no idea what they are doing, and got the same code. So apparently I have a cylinder three misfire, but it seems like my truck is running fine. Any suggestions? I tossed some lucas upper cylinder lube/ injector cleaner in about 12 gallons of fuel just to try and clean it out. Probly used about 8 of those gallons by now and still have the light on. I am going to check the plugs tomorrow (champions), but they were put on at about 103,000 miles and I am only up to 115,300 so I don't really expect them to be the problem. I also pretty much ruled out the coil packs being that I know they fire two cylinders at a time so if the coil rail was the case I would have two cylinders misfiring. Whats the deal?

[Tow--It]

Here is what I did.. Just pull the negitive off the battery for about 2 mins and that shoould reset the system.. I had the same problem..

[tjwalker]

Gotta look at things specific to that cylinder before suspecting the coil rail.

#1. Change #3 plug......cheap thing to try and you only have to replace one. Don't eliminate it from the equation because they are relatively new.
#2. Test #3 fuel injector for resistance and compare to others. Or swap it to a different cylinder.

[gilliganspl]

thanks, I am going to disconnect the battery and hope the light stays off, I forget to mention I planned on taking care of that tomorrow. And I probably even have a new spark plug sitting around, so it surely wont hurt to swap out the number three and see what happens. I will keep everyone posted. fingers crossed. Its just so weird I mean the thing starts fine, idles fine, drives fine.

[gilliganspl]

just figured I would update and say that I disconnected the battery (after some hardcore corrosion removal) and It reset the MIL. Driven quite a bit since than and have not seen it since. I also cleaned the throttle body for the hell of it.

[suprdave80]

I'm currently in the same boat, except:

Had the misfire problem, with bogged down driving, maybe six months ago. Then it went away on it's own. Now it's back with a vengeance, and is even giving me the blinking check engine light. So I will be checking injectors and replacing plugs tomorrow.

I'm not sure how it would go away and then come back, but I guess it can. Maybe the injector was intermittently bad and now it finally gave up.

Maybe you should drop new plugs in and check out the injectors anyway, so that it doesn't come back worse in the future like it has with me.

[tjwalker]

Originally Posted by suprdave80

I'm currently in the same boat, except:
Had the misfire problem, with bogged down driving, maybe six months ago. Then it went away on it's own. Now it's back with a vengeance, and is even giving me the blinking check engine light. So I will be checking injectors and replacing plugs tomorrow.

Know that the "flashing/blinking" check engine light means that your engine is experiencing a serious misfire, which if not addressed quickly, can result in damage to your catalytic converter.

Don't let this go.....

[suprdave80]

Originally Posted by tjwalker

Know that the "flashing/blinking" check engine light means that your engine is experiencing a serious misfire, which if not addressed quickly, can result in damage to your catalytic converter.

Don't let this go.....

Definitely won't be letting it go. I'm taking the day tomorrow to try and resolve it. It's kind of difficult to drive it at this point anyway, what with it shaking and bogging down.

[suprdave80]

Originally Posted by tjwalker

Know that the "flashing/blinking" check engine light means that your engine is experiencing a serious misfire, which if not addressed quickly, can result in damage to your catalytic converter.

Don't let this go.....

Definitely won't be letting it go. I'm taking the day tomorrow to try and resolve it. It's kind of difficult to drive it at this point anyway, what with it shaking and bogging down.

[default_user2]

I'm having a VERY similar issue. My Cherokee runs smooth most of the time, and starts to bog down every once in a while then the CEL comes on. Put the reader on it and it says cyl 3 misfire. It's intermittent and i've ignored it sometimes and the CEL will go off after a while and everything runs fine.

Then out of nowhere it will come back. I have a buyer for the Cherokee who's picking it up tomorrow. I don't want to sell it to him with this issue so I need to have it fixed before he picks it up. Guess I'll take it to the Jeep dealership to have them look at it. Luckily it ran like a top while he looked at it, but I know it will return...

[balloo93]

If your XJ is a 00-01 and you have the Cyl3 misfire, the problem may be that it needs a Heat shield that is covered in the TSB for these years.

The newer ign setup left a thinner wall around the #3 injector and it heats up without the shield on.

[RockRodHooligan]

http://www.wjjeeps.com/tsb/tsb_wj_1803103.pdf
TSB
1803103 - 4.0L ROUGH ENGINE IDLE AFTER RESTART FOLLOWING A HOT SOAK
Date: 09/05/03 (supercedes 1802702 dated 09/06/02)
Model Year(s): 1999-2004

Description: NOTE: This bulletin applies to vehicles equipped with a 4.0L engine. This bulletin involves the installation of a fuel injector insulator sleeve.

Details: Customers may describe a 20 to 30 second rough idle following the restart of a heat soaked engine. This condition may be most noticeable when the engine is restarted following a prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32 C (90ºF) or higher. This condition may be consistent with short city stop-and-go driving trips and can be aggravated by the use of fuel with a high ethanol content. Depending upon various conditions a MIL may occur due to DTC P0303 - Cylinder #3 Misfire.

This condition may be caused by heat from the exhaust manifold that following engine shut down migrates to the area around injector #3 and causes fuel vapor to form within the injector. This in turn may cause a momentary misfire of cylinder #3 until the fuel vapor is cleared of injector #3. The insulator sleeve lowers the injector #3 temperature to a point below which the fuel will not normally vaporize.

If vehicle exhibits a rough idle, and if a misfire of cylinder #3 is observed following a 10 to 20 minute hot soak, perform the Repair Procedure.

Parts required:
56028371AA Ignition Wire Shield

Repair procedure:
1. Cut insulator sleeve, p/n 56028371AA, to make two (2) insulator sleeves about 25-30 mm (1 in.) in length. See diagram.
2. Install one sleeve around injector #3, with the slit on the upward facing side of the injector. Install the other sleeve with the slit on the downward facing side of the injector.
3. Confirm sleeve is flush to intake manifold surface around injector.
4. Check injector #3 wire and ensure that the injector is rotated to a 2 o'clock position.


TSB for the cold start rough idle and P0303 code: TSB 18-010-01