Engine Misfire Fix - 2001 Cherokee Sport - JeepForum.com
 
LinkBack Thread Tools
post #1 of 1 Old 05-03-2016, 11:30 PM Thread Starter
getterdun
Registered User
 
Join Date: Mar 2016
Location: Summerville
Posts: 143
Engine Misfire Fix - 2001 Cherokee Sport

Summary: Engine misfire OBD codes stopped by adding new relay to run electric radiator fan when engine is running.

Condition:
  • Engine symbol illuminated on dash
  • OBD misfire codes (P030x)
  • Engine compartment too hot to raise hood after driving on warm day
Deduction Fuel is percolating in fuel rail and or fuel injectors due to proximity of exhaust manifold to intake manifold and to fuel rail, the Jeep’s high operating temperature (210°F), and the electric radiator fan only running in limited conditions.
Goal: Run the electric cooling fan whenever engine is running to cool engine compartment and eliminate fuel percolation.
Materials:
1. Bought A2C 775 Universal Automotive Relay on Amazon for about $8
2. Also used about 2 feet of 12 gauge wire
Wiring
New Relay Control circuit:
1. Cut out about 4 inches of the wire cover at right firewall to left of hood hinge to expose wires (see photo)
2. To switch the new relay on and off, located a white wire in this harness by referring to wiring diagram and testing with multimeter
a. Note: There are several white wires in this harness; any of them will probably work
3. Cut away about ˝ inch of white wire’s cover, soldered white wire from new relay to it, and wrapped with electrical tape.
4. Connected the new relay’s black wire to ground.
a. First formed loop in wire end and soldered around loop to keep wire together
b. Then unscrewed existing screw on firewall and secured wire loop with screw. See photo.
New Relay Fan Motor Circuit
1. Determined that the LB (light blue) wire in this harness is used to run the radiator fan motor.
a. Used it to avoid running a separate wire.
b. Located this wire, cut away about ˝ inch of its cover, soldered the new relay’s yellow wire to it, and wrapped with electrical tape – see photo.
2. To provide properly fused power to the LB wire, decided to use the LG/RD (light green with red stripe) wire under PDC (Power Distribution Center) – see photo
a. This is the same wire that provides power to the fan when commanded by the ECU (Engine Control Unit). Since it has a 40amp fuse, using it eliminates the need for a separate fuse.
b. Accessed the LG/RD wire at PDC
1. First removed battery terminal plastic cover at front of PDC
2. Then removed nut securing two wires under cover
3. Next released two metal tabs and lifted up PDC
4. Next removed bottom from PDC after releasing 7 plastic clips
5. Located LG/RD wire running from fan’s 40 amp fuse to existing fan relay (see photo)
  • Referred to schematic on inside of PDC to locate fuse and relay
6. Cut away about ˝” of LG/RD wire cover, soldered new red 12 gauge wire to it, and wrapped with electrical tape.
3. Connected other end of new red wire to the new relay
a. Removed the DB (dark blue) wire from new relay
b. Cut off the wire connector from DB wire and opened crimp
c. Soldered red wire to this wire connector
d. Reinserted wire connector back into relay
Relay Mount and Finish Work
1. Connected new relay to firewall using hood hinge screw (see photo)
  • First enlarged hole in new relay’s metal bracket to size of hood hinge screw
2. Put the piece of wire cover removed earlier back in place and wrapped over it with electrical tape.
How it works
  • When the engine is running, power flows from the white wire in the harness to the relay’s white wire, to relay terminal 85, through the relay’s electromagnet, to relay terminal 86, then through the relay’s black wire to ground completing the control circuit.
  • The relay’s electromagnet then causes the relay’s internal switch to connect terminals 30 and 87 and power flows from the LG/RD wire at the PDC, through the new red wire, through the new relay, to the LB wire, to the fan motor, and to ground, completing the fan motor circuit.
Note: This modification is completely unknown to the ECU. So, no unwanted OBD codes are set.
Results
  • Did it eliminate the OBD misfire codes? Yes
  • Did it cool down the engine compartment on warm day so hood can be raised without burning fingers? Yes
  • Did this mod trigger any new OBD code? No.
Credit: Thanks to all the folks who contributed to this posting which gave me the idea for this mod: http://www.naxja.org/forum/showthread.php?t=1025399

Attached Thumbnails
IMG_0097.jpg   IMG_0099.jpg  
Attached Images
 
getterdun is offline  
Reply

Tags
cooling fan , engine misfire , misfire , p0300 , p0301

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