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04JGCSpecialEdition 01-12-2013 01:21 PM

P 0303 misfire #3 4.0L
Hey guys, I have been having rough starts when the engine is warm. Today the engine light came on so I did the on/off/on/off/on and got P 0303, misfire on #3. I have changed the spark plugs maybe 5K ago. I have disconnected the negative terminal on the battery to reset it but what should I do if it comes back? I was thinking maybe the fuel injector? How difficult are they to change? If not the injector, maybe the coil pack? Looking for what step I should take first. Thanks

Frango100 01-13-2013 03:46 AM

Re: P 0303 misfire #3 4.0L
I would, to rule out the plug, swap it with an other position. At the same time you can check the color of the plug and if there is something strange at it.
You could take the injectors out and let them clean, then you also see if they are working correctly. The last step i would take is changing the coil rail.

oilslick 10-26-2014 08:27 PM

Re: P 0303 misfire #3 4.0L
I realize this is an old thread but this just started happening to me this past summer and this may be the cause:

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 (90F) 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.

fr33kster 10-28-2014 04:02 PM

Re: P 0303 misfire #3 4.0L
Maybe the PCM is bad.

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