Misfire only when hot on short trips

[JimmyO]

Hello,has anyone come across the following problem. only when the weather is hot and i drive the jeep for a couple of short trips running errands the jeep will misfire violently. If you wait only a couple of minutes it clears itself up. The engine light is on only shows misfire codes in 2 cylinders. when temperatures are moderate doesnt happen at all. I check all coils,have new plugs and all electrical connections. Jeep runs fine otherwise at all times. I havent come across another problem like this except someone suggested vapor lock in one of the injectors? i tried search here but cant find right words. any help wil be appreciated. Thanks in advance. JimmyO

[Brasscatz]

Hmmm, I wonder what a compression test of your cylinders would show? Might try to do that and let us know.

[XJ Wheeler]

There was a recall for the problem you speak of. The fix was the dealership would put a insulating blanket on the intake. Let me see what i can find.

Sent via messenger pigeon - i talk, he types.

[XJ Wheeler]

Okay, its actually a "technical service bulletin" for '00-'01 4.0L equipped XJs but it was issued for the #3 cylinder. So this may not be your issue. For more info look up "heat soak".

But here's the dealers solution. The heat shield below the fuel rail.

Attachment 3277

Here's someone else's solution. Insulation around the injectors themselves.




And here's the "tsb".

This bulletin is supplied as technical information only and is not an authorization for repair. No part of this publication may be reproduced, stored in a retreival system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, or otherwise, without written permission of DaimlerChrysler Corporation.

THIS BULLETIN SUPERSEDES TECHNICAL SERVICE BULLETIN 18-027-02,
DATED SEPTEMBER 06, 2002, WHICH SHOULD BE REMOVED FROM
YOUR FILES. THIS IS A COMPLETE REVISION AND NO ASTERISKS
HAVE BEEN USED TO HIGHLIGHT REVISIONS.

SUBJECT:
4.0L Rough Engine Idle After Restart Following A Hot Soak

OVERVIEW:
This bulletin involves the installation of a fuel injector insulator sleeve.

MODELS:
2000-2004 (TJ) Wrangler (Domestic and International Markets)
1999-2004 (WJ) Grand Cherokee (Domestic and International Markets)
2001-2004 (WG) Grand Cherokee (International Market)
2000-2001 (XJ) Jeep Cherokee (Domestic and International Markets)
NOTE: This bulletin applies to vehicles equipped with a 4.0L engine (sales code = ERH)

SYMPTOM/CONDITION:
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.

DIAGNOSIS:
1. 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:
Qty. Part No. Description

1 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.
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 (from driver’s side of vehicle).

POLICY:
Reimbursable within the provisions of the warranty.
TIME ALLOWANCE: 0.2hrs

FAILURE CODE:
AM Authorized Modification

[JimmyO]

Thank You guys.This is very helpful. Compression tests were done last year and all was well within spec, both hot and cold.The jeep runs excellent except for this problem only in hottest part of summer.I will look into which way i am going to repair this and let you know results. I have a few other little repairs to do I need to make time for.

[01xjcny]

sometimes mine will do this if i know i will be starting it in a short amount of time after turning it off i will pop the hood and it will vent off eliminating the heat soak problem. have also seen xjs in my club run a timer on the electric fan that will run till the heat is dissipated

[JimmyO]

Thanks again, I do prop hood if I will be less than a half an hour. Half an hour between stops is what I need to prevent this. I have not repaired this yet,work is killing me.Jimmy O