Misfire at high revs - JeepForum.com
 2Likes
  • 2 Post By mukluk
 
LinkBack Thread Tools
post #1 of 13 Old 07-10-2019, 09:33 AM Thread Starter
BuckBuchanan
Registered User
 
BuckBuchanan's Avatar
2002 TJ Wrangler 
 
Join Date: May 2018
Posts: 8
Misfire at high revs

I have a 2002 wrangler X. Bought about 6 months ago. When i go around 60 miles an hour for a few minutes, my check engine light starts flashing, the jeep misfires and slows to a crawl. if i shut off engine, then start again, it will drive normal again for a few miles then repeat. the codes shows random misfires. I had a mechanic changed coil, spark plugs. but did not fix it. 200 dollars plus and 3 days later , he gave up. I saw a few old threads with the same problem but did not read the solution.
Thank you kindly for your help and advice will be greatly appreciated.
Still have the same problem, took it to another "jeep" shop, he can not figure out the problem.. please help..
Thanks,
Buck

BuckBuchanan is offline  
Sponsored Links
Advertisement
 
post #2 of 13 Old 07-12-2019, 12:19 AM
mukluk
Web Wheeler
 
mukluk's Avatar
2000 TJ Wrangler 
 
Join Date: Oct 2010
Location: Clyde
Posts: 5,453
Could be carbon fouling causing valve sealing problems, see the attached TSB.
Attached Files
File Type: pdf TSB 09-003-03 Misfire.pdf (366.2 KB, 13 views)

2000 TJ SE
2005 LJ Rubicon
mukluk is online now  
post #3 of 13 Old 07-12-2019, 10:18 AM
Wolfen99
Registered User
1999 TJ Wrangler 
 
Join Date: Jun 2018
Posts: 23
Since no specifics were provided, a guess would be somewhere around O2 sensors. Changed mine last year and like a new jeep immediately.

Inside every cynical person there is a disappointed idealist.
99 TJ Sport 4.0
Wolfen99 is offline  
 
post #4 of 13 Old 07-14-2019, 11:58 AM Thread Starter
BuckBuchanan
Registered User
 
BuckBuchanan's Avatar
2002 TJ Wrangler 
 
Join Date: May 2018
Posts: 8
Quote:
Originally Posted by Wolfen99 View Post
Since no specifics were provided, a guess would be somewhere around O2 sensors. Changed mine last year and like a new jeep immediately.
Thanks, will try that next...just had the crank shaft sensor replaced...did not help
BuckBuchanan is offline  
post #5 of 13 Old 07-14-2019, 12:05 PM Thread Starter
BuckBuchanan
Registered User
 
BuckBuchanan's Avatar
2002 TJ Wrangler 
 
Join Date: May 2018
Posts: 8
Quote:
Originally Posted by mukluk View Post
Could be carbon fouling causing valve sealing problems, see the attached TSB.
i show this jeep mechanic the bulletin. he said since if you turned the engine off then restarted it, it would temporarily go away, therefore its not carbon buildup.
Thanks,
BuckBuchanan is offline  
post #6 of 13 Old 07-14-2019, 12:37 PM
mukluk
Web Wheeler
 
mukluk's Avatar
2000 TJ Wrangler 
 
Join Date: Oct 2010
Location: Clyde
Posts: 5,453
Quote:
Originally Posted by BuckBuchanan View Post
i show this jeep mechanic the bulletin. he said since if you turned the engine off then restarted it, it would temporarily go away, therefore its not carbon buildup.
Thanks,
It goes away until you get the engine back up to speed and temp where it causes the issue again, as expected. The PCM is killing the fuel to the cylinders that are heavily misfiring while you drive which explains your power loss -- this is reset when you cycle the ignition and it'll run on all cylinders again until the bad misfire reoccurs. Your description of the problem closely matches the symptoms outlined in the TSB, it'd be worth your time to at least try running a can of seafoam through and giving your Jeep an "Italian tuneup".

2000 TJ SE
2005 LJ Rubicon
mukluk is online now  
post #7 of 13 Old 07-15-2019, 10:07 PM Thread Starter
BuckBuchanan
Registered User
 
BuckBuchanan's Avatar
2002 TJ Wrangler 
 
Join Date: May 2018
Posts: 8
Quote:
Originally Posted by mukluk View Post
It goes away until you get the engine back up to speed and temp where it causes the issue again, as expected. The PCM is killing the fuel to the cylinders that are heavily misfiring while you drive which explains your power loss -- this is reset when you cycle the ignition and it'll run on all cylinders again until the bad misfire reoccurs. Your description of the problem closely matches the symptoms outlined in the TSB, it'd be worth your time to at least try running a can of seafoam through and giving your Jeep an "Italian tuneup".
Thanks, did the seafoam today...but dont know what an Italian tuneup is? Can you explain?
Thanks again,
Buck
BuckBuchanan is offline  
post #8 of 13 Old 07-15-2019, 10:38 PM
mukluk
Web Wheeler
 
mukluk's Avatar
2000 TJ Wrangler 
 
Join Date: Oct 2010
Location: Clyde
Posts: 5,453
Italian tuneup is an older term, basically meaning to drive the vehicle in a spirited/aggressive manner, winding the engine out at high rpms. The point behind it is to heat up the engine and elevate the operating pressures of the components to burn out carbon and get things moving. As noted in the TSB, when constantly driven/operated below 3200 rpm the valve train on the 4.0L is known to carbon foul and can get to the point the valves don't seal correctly -- the valves rely on the higher pressures created at elevated rpms to force the valves to spin in their keepers, preventing carbon buildup and evening wear/contact with their seats.

Did you follow the TSB directions to drive your Jeep while revving your engine to 4500rpm after the seafoam was allowed to soak for 2-3 hours?

2000 TJ SE
2005 LJ Rubicon
mukluk is online now  
post #9 of 13 Old 07-16-2019, 02:38 PM
Russ Chung
Member
 
Russ Chung's Avatar
2005 TJ Wrangler 
 
Join Date: Mar 2005
Location: Los Angeles, CA
Posts: 251
Quote:
Originally Posted by BuckBuchanan View Post
I have a 2002 wrangler X. Bought about 6 months ago. When i go around 60 miles an hour for a few minutes, my check engine light starts flashing, the jeep misfires and slows to a crawl. if i shut off engine, then start again, it will drive normal again for a few miles then repeat. the codes shows random misfires. I had a mechanic changed coil, spark plugs. but did not fix it. 200 dollars plus and 3 days later , he gave up. I saw a few old threads with the same problem but did not read the solution.
Thank you kindly for your help and advice will be greatly appreciated.
Still have the same problem, took it to another "jeep" shop, he can not figure out the problem.. please help..
Thanks,
Buck
Buck,

I assume that "random misfires" means P0300 code? A flashing check engine light (CEL) means that the Powertrain Control Module (PCM) is not working properly. Because of the flashing CEL I would focus my troubleshooting on the PCM before suspecting a sensor problem or carbon buildup. Before replacing the PCM, I would check the PCM connectors for corrosion and check the power and ground circuits.

Russ

If you don't like the way I drive, stay off the sidewalk!
KI6MLU
Russ Chung is offline  
post #10 of 13 Old 07-16-2019, 04:00 PM
mukluk
Web Wheeler
 
mukluk's Avatar
2000 TJ Wrangler 
 
Join Date: Oct 2010
Location: Clyde
Posts: 5,453
Quote:
Originally Posted by Russ Chung View Post
A flashing check engine light (CEL) means that the Powertrain Control Module (PCM) is not working properly.
Not sure where you're getting your information from, please disclose your source. Per the FSM and the owner's manual, a flashing CEL means there is a malfunction that requires immediate service, such as a misfire. Failure to attend to the fault causing the flashing CEL can result in damage to the engine or emissions system -- it is not an indication of PCM functionality or lack thereof.

2000 TJ SE
2005 LJ Rubicon
mukluk is online now  
post #11 of 13 Old 07-16-2019, 04:26 PM
Jerry Bransford
Administrator
 
Jerry Bransford's Avatar
2004 TJ Wrangler 
 
Join Date: Jan 2003
Location: Escondido, California
Posts: 71,730
One fairly common cause of misfires in newer TJ 4.0 engines that have the coil rail ignition system is someone having installed a single-tipped platinum which is where the platinum coating is on just one side of the gap. Incorrect plugs like that include the Autolite AP-985 and Champion 3034 despite some spark plug guides indicating they are ok for use. This problem is from the coil rail ignition system being a "waste spark" design which fires the plugs twice as often as needed and in alternating directions each spark. Spark plugs with different coatings on both sides of the gap have problems with waste spark ignition systems.

Three know good plugs that work fine in newer 4.0 engines like yours include the Autolite APP-985, Champion 7412 which are both double-tipped platinum plugs, or the iridium tipped Autolite XP-985 which is what I'm running in my '04 4.0 engine.

I wouldn't expect that particular misfire problem to be caused by carbon build-up where the recommended Italian Tuneup (which I do often recommend) would be the cure.

And X2 to the advice that a flashing CEL is not indicating a problem with the PCM. A flashing CEL indicates a more serious problem with the engine, often a fuel mixture problem that could cause problems for the main catalytic converter.

When you have a choice, buy American made.
Jerry Bransford is offline  
post #12 of 13 Old 07-16-2019, 06:58 PM
Russ Chung
Member
 
Russ Chung's Avatar
2005 TJ Wrangler 
 
Join Date: Mar 2005
Location: Los Angeles, CA
Posts: 251
Quote:
Originally Posted by mukluk View Post
Not sure where you're getting your information from, please disclose your source. Per the FSM and the owner's manual, a flashing CEL means there is a malfunction that requires immediate service, such as a misfire. Failure to attend to the fault causing the flashing CEL can result in damage to the engine or emissions system -- it is not an indication of PCM functionality or lack thereof.
My mistake. I realize now that I was thinking Sentry Key warning and posting about the PCM. I apologize for my mistake.

As others have posted, a flashing CEL means multiple misfires. The only time that I had the misfortune of a misfire and flashing CEL was when I had a batch of bad gas but it could be anything that is fuel or ignition related. Since it happens after you drive a few miles at highway speed, I would think it has something to do with the PCM going into "closed loop" mode.

Have you pulled the spark plugs to see if they are clean, dirty, worn? It might indicate if the mixture is too rich or too lean.

If you don't like the way I drive, stay off the sidewalk!
KI6MLU
Russ Chung is offline  
post #13 of 13 Old 07-18-2019, 06:51 AM Thread Starter
BuckBuchanan
Registered User
 
BuckBuchanan's Avatar
2002 TJ Wrangler 
 
Join Date: May 2018
Posts: 8
Thanks, I will try the Italian tuneup this weekend....i changed the spark plugs, did not help.
Thanks guys for all the suggestions, and i will try them all...
BuckBuchanan is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



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 On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome