Author Topic: Misfire when started hot - Jeep 4.0 *Fix Confirmed*  (Read 10921 times)

00XJ

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Misfire when started hot - Jeep 4.0 *Fix Confirmed*
« on: June 08, 2011, 08:02:01 AM »
Update: So the TSB about hot start misfiring refers to heat soak on the #3 fuel injector and recommends the installation of a little shield.

I ordered the part from a Chrysler dealership and installed it (no tools required), but until yesterday had not had a good opportunity to get the engine hot, run the A/C for long, and on a hot day to boot.

So yesterday, drove an hour and a half at 75mph, A/C cranked, pulled off to a gas station.. when I got back in, crossed my fingers. No misfire! That $6 part really works. It would misfire after even 10 minutes on the highway with the A/C, after sitting for a few minutes.

So, if you've got the 4.0 and you notice a miss (mine was BAD) when you restart after the engine is hot, then check out the TSB:
http://www.wjjeeps.com/tsb/tsb_wj_1803103.pdf

And get the shield, install, and be happy. It really does work, I'm amazed.




Original Post:
Seems like it only happens after I've been running the A/C, then parked, and restarted before it's had time to cool down much.

I always start the engine with ALL accessories turned off, for what it's worth.

The needle will be just above 210 from sitting, and I start it, and it misfires... BAD... for about 5 seconds until it smooths out, then it's completely normal. Behaves perfectly under driving, etc. Only really seems to happen after I've worked the A/C for a while.

Oil and coolant look good, changing spark plugs would be next.. but why could this be happening?
« Last Edit: June 19, 2011, 02:48:28 PM by 77olds »

87Warrior

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Re: Misfire when started hot - Jeep 4.0
« Reply #1 on: June 08, 2011, 08:57:23 AM »
Can you see if any codes are being stored but not triggering a CEL? Does it happen at every hot start?

My knee jerk response is the Crankshaft Position Sensor (on bell housing) or the Camshaft Position Sensor (where you would usually find the dizzy).

It is interesting that you have starting issues after using the AC. My Rubi has an intermittent rough idle that usually occurs after starting it following a long drive with AC. I have not yet found the root of the issue. Mine throws no codes, but I can't help but wonder if it may be related to the Incoming Air Temp sensor on the intake manifold getting heat soaked.

00XJ

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Re: Misfire when started hot - Jeep 4.0
« Reply #2 on: June 08, 2011, 11:26:41 AM »
Apparently it more than likely IS heat soak, and cylinder #3 is the usual suspect. There's a TSB out for it that instructs you to install a 1/4" thick silicone shield around the injector for that cylinder, and most people have said that it's cured the problem for them. I'm gonna have to swing by the Jeep dealership and ask them where I can get the shield. Some people have said using heat shield tape or padding has not helped for them.

Here's what I found doing a Google search:

Quote
Your Jeep has coli packs, there are no ignition wires to replace. The first thing i would do is replace the plugs IE: A tune up, with a fuel system service. You're doing a fuel system service because you may have a plugged/dirty injector causing the misfire. If you find that its not a maintenance item, this problem fits you cylinder #3 misfire to a T:

The intake manifold of the 2000 and 2001 Jeep Cherokees, and other Jeep vehicles with the 4.0L, was redesigned in 1999. With the redesign of the intake manifold, the fuel injector for cylinder #3 was moved too close to the exhaust manifold.

When the vehicle is driven the exhaust heats up tremendously, then when the vehicle is shut off, the temperature under the hood rises (its called a hot soak) because the cooling system is no longer running. During the hot soak, radiant heat from the exhaust manifold actually boils the fuel inside the injector, creating air bubbles. When you turn the vehicle on after the hot soak the injector is not flowing enough fuel for the cylinder to fire (because its not squirting fuel, ist squirting some fuel and a lot of air) and the cylinder misfires.

Accounts of this problem are very well documented by Jeep, and there is a Technical Service Bulletin regarding this issue. You need TSB 18-031-03, easily locatable here:

http://www.wjjeeps.com/tsb/tsb_wj_180310

To complete the repair you need the part listed on the TSB, PN# 56028371AA. As outlined in the TSB, its actually an ignition wire heat shield that you'll be installing around the injector to insulate it from the heat of the exhaust. The installation should take 15-20 min. Its very easy to do, just follow the instructions on the TSB. I've done more of these than i care to think about. The part can be picked up at a dealership for $10 or less.
Source(s):
5 year as Chrysler Jeep tech and over all Jeep nut.

Will have to look into this. Not throwing a code... I wonder if the bulb was removed because the previous owner had this issue and wanted to ditch the Jeep before it cost him money?

Another source (Jeep TSB found on a Ford forum, go figure)

http://www.fordforum.org/hot-start-misfire-dtc-p0303-t13039.htm

Quote
I've been having issues with the #3 cylinder misfiring when restarting after vehicle has been sitting hot. Took vehicle to dealer, dealer to me to bank for $900 in repairs (wire, coil module, injector cleaner, carbon cleaning) and had the same problem the next day. I didn an online search and found the correct diagnosis to my problem. Although this was for JEEP, it is the exact problem I am having:

Fuel System - Hot Start Misfire/MIL ON/DTC's/Rough Idle

NUMBER: 18-031-03

GROUP: Vehicle Performance

DATE: Sep. 05, 2003

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 ********S 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 32C (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.

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

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.

« Last Edit: June 08, 2011, 11:46:49 AM by 77olds »

87Warrior

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Re: Misfire when started hot - Jeep 4.0
« Reply #3 on: June 08, 2011, 12:16:04 PM »
I remember when that TSB came out. My father had a 2000TJ and just thew the notice away. I never gave much thought to it other than my pops Jeep needed the shield. This could very well be the cause of my TJs rough idle, even with the shield. Thanks for the help... In your held thread none the less.

The CEL is an LED soldered into the instrument panel. There could be a vacuum cap over the bulb or tape behind the display. It should light up when you start it.

Onyx Dragon

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Re: Misfire when started hot - Jeep 4.0
« Reply #4 on: June 08, 2011, 12:54:53 PM »
I remember when that TSB came out. My father had a 2000TJ and just thew the notice away. I never gave much thought to it other than my pops Jeep needed the shield. This could very well be the cause of my TJs rough idle, even with the shield. Thanks for the help... In your held thread none the less.

The CEL is an LED soldered into the instrument panel. There could be a vacuum cap over the bulb or tape behind the display. It should light up when you start it.

See, this is why I like my model year.  Yeah the bulbs go out, but it made it a snap to get the cluster out and put the sport cluster in :lol:

87Warrior

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Re: Misfire when started hot - Jeep 4.0
« Reply #5 on: June 08, 2011, 01:00:47 PM »
The back light, turn signal indicators and bright light indicator have replaceable bulbs. But yeah, it sucks the others are soldered to the board. Though they are easily accessible and can be replaced by a competent person.

00XJ

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Re: Misfire when started hot - Jeep 4.0
« Reply #6 on: June 08, 2011, 01:27:48 PM »
I haven't even paid attention if it comes on during start up, I usually only watch if a light doesn't turn back off :lol:

I'll have to watch for it.

Onyx Dragon

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Re: Misfire when started hot - Jeep 4.0
« Reply #7 on: June 08, 2011, 04:25:27 PM »
The back light, turn signal indicators and bright light indicator have replaceable bulbs. But yeah, it sucks the others are soldered to the board. Though they are easily accessible and can be replaced by a competent person.

Yeah, but that takes more time.

Meatywand

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Re: Misfire when started hot - Jeep 4.0
« Reply #8 on: June 08, 2011, 05:00:25 PM »
Mine started doing this before the coil pack went dead, no A/C since last September so can't comment on that, but the coil pack is only 100 bucks and maybe 30 minutes of work.
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Joshua

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Re: Misfire when started hot - Jeep 4.0
« Reply #9 on: June 08, 2011, 07:00:47 PM »
The back light, turn signal indicators and bright light indicator have replaceable bulbs. But yeah, it sucks the others are soldered to the board. Though they are easily accessible and can be replaced by a competent person.

I don't even know of any mechanics that know how to solder. :lol:

I know how to, but I just use butt connectors and heatshrink, mostly because it is faster and MUCH easier to do for in-vehicle repairs.
...and either quite drinking or quite posting because you're going into some sort of weird AMERICA 1776 FUCK YEAH mode.

87Warrior

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Re: Misfire when started hot - Jeep 4.0
« Reply #10 on: June 08, 2011, 11:50:23 PM »
Nick - Here is a copy of the current TSB http://www.wjjeeps.com/tsb/tsb_wj_1803103.pdf

Mine started doing this before the coil pack went dead, no A/C since last September so can't comment on that, but the coil pack is only 100 bucks and maybe 30 minutes of work.
You know, this was my initial thought...last year when the rubi started doing this. I don't know how long the coil packs can sit in limbo before they completely die, but I suspect it is not a year. I think the issue is commonly associated with A/C since it occurs more regularly when the ambient air temp is 90+, when most folks are using the A/C.
I don't even know of any mechanics that know how to solder. :lol:
I know how to, but I just use butt connectors and heatshrink, mostly because it is faster and MUCH easier to do for in-vehicle repairs.
Really? I learned how to solder in 7th grade as part of a technology course. Its probably the only thing I remember from middle school  :lol:

I solder/heat shrink everything, even in vehicle stuff. Just get the iron plugged in before starting any of the work and it doesn't take much more time than those butt connectors.  Currently I am cutting/splicing/soldering/heat shrinking up a storm on the XJ interior harness for the Comanche. Reworking all of the shitty factory splices too. I don't want those so little gremlins to show up and get me.
« Last Edit: June 08, 2011, 11:56:09 PM by 87Warrior »

00XJ

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Re: Misfire when started hot - Jeep 4.0
« Reply #11 on: June 09, 2011, 10:32:44 AM »
Yeah I got on AllData here at work and printed off the TSB, then went to the local Chrysler dealership to order the part (my own dealership would have marked it up 10%, the Chrysler dealership sold it to me at cost ::) )

Part should be in today, I'll put it on and let you all know if it helped.

87Warrior

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Re: Misfire when started hot - Jeep 4.0
« Reply #12 on: June 09, 2011, 11:06:46 AM »
How much did the part cost? I would guess not much, just curious.

I wonder if putting the part on each injector would have any benefit. I know when I stick a header on my MJ I don't want any heat soaking issues.

00XJ

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Re: Misfire when started hot - Jeep 4.0
« Reply #13 on: June 09, 2011, 11:22:40 AM »
How much did the part cost? I would guess not much, just curious.

I wonder if putting the part on each injector would have any benefit. I know when I stick a header on my MJ I don't want any heat soaking issues.

$7.12 out the door. Once I get it I'll take pictures of it, I'm sure you could just make your own... but I wanted the real thing to know exactly how it's designed before I tried that.

I'm also considering putting them on every injector.

00XJ

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Re: Misfire when started hot - Jeep 4.0 *Fix Confirmed*
« Reply #14 on: June 19, 2011, 02:50:51 PM »
Seems like such a simple fix...

I should've taken a picture of it with my phone. It looks like white plastic wire covers, ribbed like wiring conduit, but it's made out of some sort of fiber type material. About half inch diameter. You cut off two 1" sections, place one on the injector with the slit facing up, then the other goes over top of that with the opening facing down.

It's that simple. Kind of a bitch to get them on there since there isn't much room to fit your hands, but you can do it without removing anything. No tools required besides a knife to cut the shield.

First post updated because I can confirm that it fixed the problem.

Onyx Dragon

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Re: Misfire when started hot - Jeep 4.0 *Fix Confirmed*
« Reply #15 on: June 23, 2011, 04:59:50 PM »
I wonder what changed so that it causes this issue in the 00-01 XJ, but not the earlier models.

00XJ

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Re: Misfire when started hot - Jeep 4.0 *Fix Confirmed*
« Reply #16 on: June 23, 2011, 05:23:44 PM »
I wonder what changed so that it causes this issue in the 00-01 XJ, but not the earlier models.

When did they switch from TBI to fuel injection?

Onyx Dragon

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Re: Misfire when started hot - Jeep 4.0 *Fix Confirmed*
« Reply #17 on: June 23, 2011, 05:30:10 PM »
When did they switch from TBI to fuel injection?

Not sure, but my 95 has FI.

87Warrior

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Re: Misfire when started hot - Jeep 4.0 *Fix Confirmed*
« Reply #18 on: June 23, 2011, 07:44:30 PM »
1987 was when the Renix fuel injection system was introduced. 1991 was when the Mopar obdi fuel injection system was introduced. 95/96 was when the Mopar obdii (partial) was introduced. 1997 was the introduction of Mopars true obdii system. The 4.0 NEVER had TBI in a Jeep. The 2.5 did have TBI for a few years, but switched to FI in 1987 (I may be wrong about the 2.5 dates, never paid too much attention).

In 2000, they switched to a new exhaust manifold. This new version was a two piece design to reduce the likelihood of cracking at the manifolds collector. It was used from 00-06. (long live the 4.0 >:() This also forced a slight redesign at the bottom portion of the intake manifold to allow room for the new two piece manifold. According to the TSB heat works its way through the intake manifold and soaks the #3 injector. My guess is the new intake/exhaust manifolds resulted in the heat soak. 

In 00 they also did away with the dizzy and implemented a coil rail assembly.

00XJ

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Re: Misfire when started hot - Jeep 4.0 *Fix Confirmed*
« Reply #19 on: June 23, 2011, 07:49:20 PM »
1987 was when the Renix fuel injection system was introduced. 1991 was when the Mopar obdi fuel injection system was introduced. 95/96 was when the Mopar obdii (partial) was introduced. 1997 was the introduction of Mopars true obdii system. The 4.0 NEVER had TBI in a Jeep. The 2.5 did have TBI for a few years, but switched to FI in 1987 (I may be wrong about the 2.5 dates, never paid too much attention).

In 2000, they switched to a new exhaust manifold. This new version was a two piece design to reduce the likelihood of cracking at the manifolds collector. It was used from 00-06. (long live the 4.0 >:() This also forced a slight redesign at the bottom portion of the intake manifold to allow room for the new two piece manifold. According to the TSB heat works its way through the intake manifold and soaks the #3 injector. My guess is the new intake/exhaust manifolds resulted in the heat soak. 

In 00 they also did away with the dizzy and implemented a coil rail assembly.

That makes sense. Yeah it's totally misfire free now, even on scorching days and long trips with the A/C on full blast. I still can't believe how easy it was.