so i dont know where to even start . i got a 2000 jeep Cherokee sport with a cylinder 3 misfire it had a misfire when i got it so i replaced the spark plugs coil pack and crank position sensor.it did not fix the issue so i took it to my local auto shop they found bad grounds from the computer and improperly gapped spark plugs. they fixed it and sent me on my way .. 20 miles later cylinder 3 misfire is back and the check engine is on with code for p0303. the auto shop is telling me they have no clue why they tested compression in all cylinders it was all 120 they said fuel pressure is good all the injectors are working they said all the coils are firing and they honestly dont know what to tell me im lost ... i am near destroying this jeep its draining my wallet anyone have any ideas?

 

Look up '2001 Jeep Cherokee heat soak'.

 

And how are your plug wires?

 

Heat soak TSB below. You don't have plug wires. Could also try swapping #3 injector with another, see if the problem follows. Vacuum gauge to check for a lazy valve spring would be another idea.



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.