tach spiking, engine stumples when going over bumps - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Grand Cherokee & Commander Forums > ZJ Grand Cherokee Forum > tach spiking, engine stumples when going over bumps

Spartan Locker Promo Running now @ ROCKRIDGE 4WD plus FREEG2 Disc Brake Conversion Kit for Jeep Wrangler YJ TJ LJ ChTJ Wrangler 4" Rough Country Suspension Lift Kits in

Reply
Unread 05-08-2014, 06:00 PM   #1
dean477
Registered User
1998 ZJ 
 
Join Date: Aug 2010
Location: Los Angeles, California
Posts: 168
tach spiking, engine stumples when going over bumps

Hey guys, Ive had this problem with my jeep for over a year now and attributed it to a lot of broken parts that i have now recently repaired/replaced/upgraded.

SIGNS AND SYMPTOMS

While going over bumps, potholes, or particularly bouncy stretch of highway, my tachometer will spike up anywhere from 500-2000 rpm in a quick flash. It has no relation to actual engine rpms rising.
Recently I've started to notice that while going over the same bumps that cause the Tach spike, it also causes the engine to slightly stumble(i hear a clunk or two that sounds like an engine when it is fighting to not stall).
Another possible related symptom is when im on the highway going, say 55 in 4th(OD), and i hit a bumpy stretch, the jeep shifts to 3rd and then back to 4th.

RELATED REPAIRS

In recent months ive replaced the pcm, o2 sensors, map, iac, and coolant temp sensors.
the crankshaft sensor was replaced a couple years ago to fix a stalling problem that i eventually found out was my pcm. ALL SENSORS MOPAR.
Kolak ignition in 2013. Battery terminals on tight and grounds are clean.


QUESTION

Does anyone have any experience with the tach spiking? Is it related to the stumbling? Is it related to dropping out of gear when cruising over a bump? My jeep is also running very rich

Thanks for reading!
Dean

dean477 is offline   Reply With Quote Quick reply to this message
Unread 12-10-2014, 11:33 AM   #2
Elkaholic
NMElkaholic
 
Elkaholic's Avatar
1998 ZJ 
 
Join Date: Nov 2007
Location: Rio Rancho, NM
Posts: 477
Did you ever figure this out?? I am having same issues...
__________________
98 5.9, Platinum 4.5 RE SF all adjustable arms, RE Monotube Shocks, Carolina front drive shaft, Pro Comp Extream Alloys Stryker's, 285/75/16 BFG's KM2's,Stage 1 rock sliders,Confer roof rack,Warn XD9000i winch, 3" Kolak exhaust system, Addco front swaybar and lot's more goodies.. 79 CJ5 AMC 304 33x12.5 Pro Comp X-tream mud tires on 15x12 MT classics. 3" lift.
Elkaholic is offline   Reply With Quote Quick reply to this message
Unread 12-10-2014, 11:35 AM   #3
kg6mov
Web Wheeler
 
kg6mov's Avatar
1996 ZJ 
 
Join Date: Nov 2012
Location: Cupertino, CA
Posts: 3,262
Sounds like an electrical connection somewhere that is confusing the PCM.
__________________
1996 ZJ Green Laredo V8, 2.5" OME and Bilsteins, 31's, Holes drilled in the roof.
1998 ZJ Platinum Limited 5.9, New engine and trans, no front driveshaft, but it's pretty

"Whats wrong with a PT Cruiser?"
"Coulda had a V8!"

96 build thread

Niner build thread

Quote:
Originally Posted by Texas ZJ1 View Post
I heard someone yell "mall crawler" from the back porch. I'll go see who said that. Be right back.
kg6mov is online now   Reply With Quote Quick reply to this message
Unread 12-11-2014, 04:58 AM   #4
ZeeJay1997
Registered User
1997 ZJ 
 
Join Date: Dec 2008
Location: Sweet Home, Alabama
Posts: 6,890
wiggle the pcm connectors and tap on the pcm while engine is running. if problem is duplicated, it could be bad solder joints or loose contacts in a connector

see link below for more info
ZeeJay1997 is offline   Reply With Quote Quick reply to this message
Unread 12-11-2014, 05:09 PM   #5
dean477
Registered User
1998 ZJ 
 
Join Date: Aug 2010
Location: Los Angeles, California
Posts: 168
on the passenger side of the engine towards the back(closer to cabin) there is wiring that grounds onto the engine block. I believe I followed the wiring from the transmission up to the pcm and it comes out of that harness. I took off the bolt, cleaned it with degreaser and tightened it back on there. I am not 100% confident this is it because the problem seemed to go away for a couple months but ive developed quite the oil(and at one point coolant) leak and the problem has returned but far less frequently.


Hope this works for you and thanks for reminding me to clean mine today...


Edit: i just saw the you have a 5.9... I have a 4.0 so im not sure about the location of that ground. I would follow the wiring harness up from your trans to see where it grounds out. Clean it and test again.

If it were me... I would clean all the grounds in the engine bay, one at a time(test driving) so that when you find the problem you know where to go when it starts happening again.
dean477 is offline   Reply With Quote Quick reply to this message
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.
Note: All free e-mails have been banned due to mis-use. (Yahoo, Gmail, Hotmail, etc.)
Don't have a non-free e-mail address? Click here for a solution: Manual Account Creation
Email Address:

Log-in

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






Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.