Can you run without an ECU? - 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 Cherokee & Comanche Forums > XJ Cherokee Technical Forum > Can you run without an ECU?

Introducing MONSTALINER™ UV Permanent DIY Roll On Bed LineThe Solution to Radius Arm Bind - Meet Lock-N-LoadFS: Jeep Fog Light LED Bulbs! Several Brightness Options!

Reply
Unread 02-19-2013, 06:38 PM   #1
aldersonfilm
Registered User
1998 TJ Wrangler 
 
Join Date: Jun 2012
Location: Pasadena, CA
Posts: 186
Can you run without an ECU?

Is it possible to still start and drive if the ECU is damaged or missing entirely?

aldersonfilm is offline   Reply With Quote Quick reply to this message
Unread 02-19-2013, 07:25 PM   #2
mtwask01
Registered User
1995 XJ Cherokee 
 
Join Date: Aug 2010
Location: Louisville, KY
Posts: 97
Only if you retrofit to a carburetor. The ECU is the brain of the fuel injection system and is absolutely necessary. If it is damaged, it may still run and drive depending on the severity of the damage, but if missing entirely, it absolutely will not run.
mtwask01 is offline   Reply With Quote Quick reply to this message
Unread 02-20-2013, 11:35 AM   #3
sAe23
Registered User
1995 XJ Cherokee 
 
Join Date: Apr 2009
Location: Los Angeles / SFV, California
Posts: 2,469
You'd probably have to change the distributor too, and who knows what else...

OP, why not just unplug it and see for yourself ?
sAe23 is offline   Reply With Quote Quick reply to this message
Unread 02-20-2013, 12:31 PM   #4
Pats94
Registered User
2001 XJ Cherokee 
 
Join Date: Mar 2012
Location: Des Moines, Ia
Posts: 421
Go to a carb, distributor set up. If you have a auto thats going to need to be addressed.
__________________
If its stock it sucks and if it scares the hell outta ya its just about right!
Pats94 is offline   Reply With Quote Quick reply to this message
Unread 02-20-2013, 04:56 PM   #5
tjwalker
It's the crank sensor!
 
tjwalker's Avatar
1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,467
Gotta know.....why are you asking?
__________________
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
tjwalker is offline   Reply With Quote Quick reply to this message
Unread 02-20-2013, 06:38 PM   #6
aldersonfilm
Registered User
1998 TJ Wrangler 
 
Join Date: Jun 2012
Location: Pasadena, CA
Posts: 186
Haha this was purely a curiosity question. I pulled the battery cable while the engine was running to check the alternator, but I then heard that this can damage the ECU. Just making sure, I didn't do that.
aldersonfilm is offline   Reply With Quote Quick reply to this message
Unread 02-20-2013, 10:57 PM   #7
Reptile
Web Wheeler
1991 XJ Cherokee 
 
Join Date: Feb 2011
Location: Bakersfield, CA
Posts: 1,297
Quote:
Originally Posted by aldersonfilm View Post
Haha this was purely a curiosity question. I pulled the battery cable while the engine was running to check the alternator, but I then heard that this can damage the ECU. Just making sure, I didn't do that.
So you ignored a warning that it could damage your ECU and still proceeded to do it??

Sure it'll run without a ECU, I don't see why not, at least on a downward slope. Say, why don't you cut off some random wires and let us know what you get away with?
Reptile is offline   Reply With Quote Quick reply to this message
Unread 02-21-2013, 12:14 AM   #8
aldersonfilm
Registered User
1998 TJ Wrangler 
 
Join Date: Jun 2012
Location: Pasadena, CA
Posts: 186
Didn't hear it could damage the ECU until I had already tried pulling the cable. Seems to be running fine though.
aldersonfilm is offline   Reply With Quote Quick reply to this message
Unread 02-21-2013, 04:26 AM   #9
Hudson
Registered User
1999 XJ Cherokee 
 
Join Date: Mar 2010
Location: New Milford, Connecticut
Posts: 785
Get a multimeter and check the alternator that way.

Your battery should be at like 14.55 DC volts with a good alternator. (With engine running obviously). With engine off it should drain down to like 12.55 DC volts and not much lower.

Most auto stores will test alternators for you for free if you don't have a multimeter.
__________________
Live To Die. You're Not Going To Get Out Of This One Alive.

Build Thread - http://www.ausjeepoffroad.com/forum/showthread.php?t=121903
Hudson is offline   Reply With Quote Quick reply to this message
Unread 02-21-2013, 05:43 AM   #10
Kettles
Registered User
2001 XJ Cherokee 
 
Join Date: May 2009
Location: Louisville, Kentucky
Posts: 4,177
I dont know why the cable off would damage the ECU, unless the voltage regulator was bad and without the battery it somehow started generating excess voltage. But not knowing the specifics on how it works, I cant say either way if that would happen.

But I do know, if the alternator is functioning properly, the engine will run without a battery and it shouldn't hurt anything (not start mind you, but you probably knew that). The ECU controls everything, if its not there/not working, nothing works.
__________________
_=====o000o
//__l_l_,\____\,____
l_--\_l__l_/--|lllll|
_.(o)_)__.(o)_)--o-)_)
"Dee", a Patriot Blue 2001 Cherokee Sport 4.0L High-Output Pictures Build Thread
The Rocket Sheep
"Live Free Or Die; Death Is Not The Worst of Evils." -General John Stark
Quote:
Originally Posted by speedbucket View Post
perfect depends on how far away you are when you look at it:D
Quote:
Originally Posted by Millermagic View Post
It's a 4.0 ... as long as there's something in the crank case that isn't coolant I'm sure it will still run forever.
Kettles is offline   Reply With Quote Quick reply to this message
Unread 02-21-2013, 09:33 AM   #11
tjwalker
It's the crank sensor!
 
tjwalker's Avatar
1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,467
Below is a link to a good article that explains why you should not remove a battery cable on a running engine. I've fixed a couple of vehicles where it fried either the computer, the alternator, or both. Doesn't happen all the time, but why would you want to take the chance when the charging system can efficiently be tested with a simple meter.....

http://www.troubleshooters.com/dont_...ct_battery.htm
__________________
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
tjwalker is offline   Reply With Quote Quick reply to this message
Unread 02-21-2013, 05:10 PM   #12
Kettles
Registered User
2001 XJ Cherokee 
 
Join Date: May 2009
Location: Louisville, Kentucky
Posts: 4,177
__________________
_=====o000o
//__l_l_,\____\,____
l_--\_l__l_/--|lllll|
_.(o)_)__.(o)_)--o-)_)
"Dee", a Patriot Blue 2001 Cherokee Sport 4.0L High-Output Pictures Build Thread
The Rocket Sheep
"Live Free Or Die; Death Is Not The Worst of Evils." -General John Stark
Quote:
Originally Posted by speedbucket View Post
perfect depends on how far away you are when you look at it:D
Quote:
Originally Posted by Millermagic View Post
It's a 4.0 ... as long as there's something in the crank case that isn't coolant I'm sure it will still run forever.
Kettles is offline   Reply With Quote Quick reply to this message
Reply

Tags
computer , ecu , sensor , wiring

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.