my 2.5L engine is running lean- what's happening? - 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 Wrangler Forums > YJ Wrangler Technical Forum > my 2.5L engine is running lean- what's happening?

TeraFlex Now at Rockridge 4WD! BEST DEALS around!Alloy usa heavy duty ball joint kitsENGO QUADLUX 6" to 54" LED AMBER AND WHITE MULTI

Reply
Unread 08-09-2010, 02:22 AM   #1
castaway74
Registered User
 
Join Date: Jan 2010
Location: santa cruz, CA
Posts: 15
my 2.5L engine is running lean- what's happening?

A few months ago, I noticed my 1994 2.5L Jeep engine rpms dropping into the 500rpm range, and the engine seemed to stumble occasionally. Changed the plugs, cap and rotor, but no change. Air filter is in good shape. I checked the engine codes and got contradictory codes- 02 SENSOR DETECTS A LEAN CONDITION, AND 02 SENSOR DETECTS NEITHER A RICH NOR LEAN CONDITION. After replacing the 02 Sensor, lo and behold, the codes remained the same- changing the O2 CHANGED NOTHING. The engine still behaves the same, and seems to stumble and run leaner in colder temperatures, and better and smoother when it's warm. What is going on? I know there is no idle adjustment possible for this engine, so now what?

castaway74 is offline   Reply With Quote Quick reply to this message
Unread 08-09-2010, 05:36 AM   #2
Karma
Registered User
1989 YJ Wrangler 
 
Join Date: Jun 2006
Location: White Rock, NM
Posts: 860
HI
How do you really know it is actually running lean? One way to tell is by the color of the spark plugs. Pull the plugs (keep the wires straight, don't get them mixed up, mark them). Examine the electrodes. a clean running engine with the right mixture ratio should show light tan. Lean will show white or gray. Rich will be black and sooty. You should make this check after you have driven the vehicle for 1/2 hour. Let it cool then pull the plugs.

This is a good place to start. Once you have varified the running mixture you can start to troubleshoot.

Sparky
Karma is offline   Reply With Quote Quick reply to this message
Unread 08-09-2010, 10:28 AM   #3
5.7YJ
Senior Member
 
5.7YJ's Avatar
1987 YJ Wrangler 
 
Join Date: Aug 2006
Location: Rockledge, Florida
Posts: 900
Check for vacuum leaks. Start with looking at vacuum lines and then check your intake manifold gasket. Sometimes the intake bolts will be loose and you can just tighten them down if the gasket hasn't been ruined.
5.7YJ is offline   Reply With Quote Quick reply to this message
Unread 08-09-2010, 03:00 PM   #4
GottaYJ
Registered User
1995 YJ Wrangler 
 
Join Date: Jul 2010
Location: Phoenix, Arizona
Posts: 285
Crack in the exhaust manifold or leaking behind the gasket would confuse the o2 sensor
GottaYJ 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


Suggested Threads





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.