Occasional Misfire

I have had an occasional misfire in my jeep for about 6 months now. i just replaced the head (0331 crack :firedevil) and i had always assumed the misfire was because of the coolant in the cylinders. However it just did it again to me. Normally when it misfires i can shut it off and it will start up correctly. But not today, it wouldn't run right. So i let it sit for about and hour, and then it started right up and ran perfectly.

2001, I6, 126,000

After some research I have decided it would be best to replace the spark rail, as I dont think it has ever been replaced. Any other ideas?

Before replacing anything, lets talk about conditions.

Did this happen after the engine was hot, and then shut off for a relatively short period of time?

There is a problem called "heat soak" prevalent in the 99-01 models. Essentially things are too hot at cylinder number 3 injector and it creates a situation like vapor lock in that injector.

Quick and dirty test for heat soak: Get the engine good and hot, park and shut off the engine. Open the hood and let cool for 30 minutes. Start it up, if the symptoms are gone or greatly reduced, you have heat soak.

Post back with results, or if this doesn't sound like your problem, try and post additional details about what is happening.

And if you have ever seen a check engine light, you MUST pull codes for guidance. Post the exact code number here for comment.

Codes are stored, even with no current check engine light. Here are some TSBs to take a gander at.

2000-2001 Rough Idle TECHNICAL SERVICE BULLETINS: ROUGH IDLE / MULTIPLE CYLINDER MISFIRE

1801301 - ROUGH IDLE AT COLD TEMPERATURES
Date: 06/11/01
Model Year(s): 2000

Description: Some vehicles may exhibit a rough idle and / or Malfunction Indicator Lamp (MIL) light on condition upon initial start-up after a cold soak when temperatures are below 50 degrees F (10 degrees c). This bulletin involves selectively erasing and reprogramming the Control Module (PCM) with new software (Cal level 00Cal15C).

1801001 - ROUGH IDLE AT COLD TEMPERATURES
Date: 04/20/01
Model year(s): 2001

Description: THIS BULLETIN APPLIES TO VEHICLES BUILT PRIOR TO APRIL 30, 2001 AND CALIBRATION LEVEL PRIOR TO (LESS OR LOWER THAN) THOSE LISTED IN THE OVERVIEW ABOVE. This bulletin involves selectively erasing and reprogramming the Powertrain Control Module (PCM) with new software (WJ/TJ ? calibration level 01Cal14C, XJ ? calibration level 15B.)

I'm reaching back a few years in memory, but I remember on my old 2001 I got a tsb 'fix' from the dealer, which was basically wire loom about 2" long, but not the normal wire loom material. It was placed somewhere on the driver's side of the engine over an injector to help with 'heat soak'. As far as I remember, the simple fix did help.

Here is the heat soak TSB.

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

JrTxJ said:

I'm reaching back a few years in memory, but I remember on my old 2001 I got a tsb 'fix' from the dealer, which was basically wire loom about 2" long, but not the normal wire loom material. It was placed somewhere on the driver's side of the engine over an injector to help with 'heat soak'. As far as I remember, the simple fix did help.

Click to expand...

Yep. That was the TSB for heat soak. Fairly ineffective for most.

There was a switch from Champion to NGK plugs too.

The real key on heat soak is reducing the underhood temperature after the engine is shut down. The most effective method is to add a timer to the efan circuit that will run the efan for 5 minutes or so after the ignition is shut off.

Wow you guys are awesome! thanks for all the info!

It was really cold when i started it, and thats when i have always noticed the misfire. It was parked for probably 24 hours outside, in a snow storm and a cold night. I havent had a chance to pull the code yet. I will get it down to autozone and do that ASAP.