Misfire question - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > TJ Jeep Wrangler Forum > TJ Tech Forum

Join Wrangler Forum Today

Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 09-01-2010, 01:22 PM   #1
CenARJeepChick's Avatar
Join Date: Jan 2009
Location: Central Arkansas
Posts: 136
Misfire question

Hi guys, I'd like some input-mainly to validate my own conclusion before I start buying parts.

Last week I was driving home from work-70ish on the interstate and all of a sudden she (2002 Wrangler-4.0l) fell on her nose and started misfiring-vibrating like crazy under throttle and the the check engine light started flashing. I slowed down to about 55 and she was better but obviously still missing. I was meeting my parents for dinner so I checked the codes and pulled a 300 (misfire detected-duh), 301-cylinder #1 misfiring and 304-cylinder #4 misfiring. When I came out of the restaurant I wanted my dad to listen to her. Started up and ran smooth as a kitten purring. I periodically rechecked the codes over the next few days and they were still there but I hadn't felt the engine misfire. So I chocked it up to moisture since I had cleaned up the engine the day before at the car wash.

But its never that easy. Coming to work this morning it misfired a few times. Nothing as severe as the first time but I could feel the occasional stutter on the interstate. I'm thinking coil rail instead of injectors since cylinders #1 and #4 are companion cylinders and share a coil pack. Unfortunately it looks like I have to buy the whole rail instead of just one coil pack.
So aside from changing the plugs while I've got it apart does anyone have another suggestion or does this sound on target?

CenARJeepChick is offline   Quote Quick Reply
Old 09-01-2010, 01:33 PM   #2
pokey's Avatar
Join Date: Feb 2010
Location: backroads of the Mojave
Posts: 1,106
This might sound too simple but check your battery and connections. A weak battery will cause an engine to run rough. If your battery is almost shot the alternator isn't enough to keep the engine running smoothly.

. . . . picking the lines with my twenty-nines . . . .

'99 sport 4.0 5 speed, top-of-the-line floormats
pokey is offline   Quote Quick Reply
Old 09-01-2010, 01:38 PM   #3
Knows a couple things...

WF Supporting Member
Jerry Bransford's Avatar
Join Date: Nov 2005
Location: Escondido, Calif.
Posts: 30,849
Images: 2
Originally Posted by pokey View Post
This might sound too simple but check your battery and connections. A weak battery will cause an engine to run rough. If your battery is almost shot the alternator isn't enough to keep the engine running smoothly.
X2. The TJ's alternator won't put ANY power out if the battery is dead, and it will put out weak power if the battery is weak. Without a good battery, the engine either won't run or it will run badly depending on the battery's condition.

Yes we know that SOME vehicle alternators and all generators will run fine with a dead or weak battery, just not the type of alternator used in the Wrangler.

If it's not the battery or a loose/dirty/corroded battery connection (no, a visual check is not good enough to tell if it's ok), then odds are fairly good that either the crankshaft position sensor or camshaft position sensor has gone bad.
When you have a choice, buy American.

Jerry Bransford is online now   Quote Quick Reply
Old 09-01-2010, 02:16 PM   #4
Join Date: Aug 2008
Posts: 2,473
Always 1 & 4 - companion cylinders, not other cylinders?
Just washed it down.

Remove the coil rail - look closely at the boots and plugs on those 2 for signs of dirt. Clean as needed.
Reassemble with a touch of Silicone Dielectric grease on the boots.

And - have a friend with good hearing listen carefully for the telltale "snap" "snap" of the coil breaking down.

If it starts misfiring constantly, check underneath with an infrared thermometer on those 2 cylinders. One will be too hot, the other too cold - compared to the other cylinders.
It's no wonder the country is falling apart - stupidity abounds!
rrich is offline   Quote Quick Reply
Old 09-01-2010, 03:18 PM   #5
CenARJeepChick's Avatar
Join Date: Jan 2009
Location: Central Arkansas
Posts: 136
Battery was replaced in June. Crank and cam position sensors have both been replaced within the year. Both sensors threw codes specific to them and when the battery went your right it wouldn't do anything. I'll pull the rail and inspect as recommended. Thanks.
CenARJeepChick is offline   Quote Quick Reply

Quick Reply

Register Now

In order to be able to post messages on the Jeep Wrangler Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Misfire Question CenARJeepChick YJ Tech Forum 1 09-01-2010 01:16 PM
6sp shift question rico334 TJ Tech Forum 15 12-13-2009 09:08 PM
Trans Mount Question MOz TJ Tech Forum 8 06-10-2008 03:14 PM
Runing rough, idle rough, cylinder #4 misfire spdrcrpete TJ General Discussion Forum 13 06-02-2008 01:32 PM
Carb question and EGR question trulefty YJ Tech Forum 0 12-12-2006 04:55 PM

» Rates
Get low rates on auto insurance in Canada!

» Network Links
»Jeep Parts
» Featured Product

All times are GMT -5. The time now is 09:53 PM.

Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, and Grand Cherokee are copyrighted and trademarked to Chrysler Motors LLC.
Wranglerforum.com is not in any way associated with the Chrysler Motors LLC