Jeep Tech - Ignition upgrade for more power in the Jeep 4.2Liter (258 ci) I6 Engine - Jeep at Off-Road.com
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Jeep TechIgnition upgrade for more power in the Jeep 4.2Liter (258 ci) I6 Engine
Publish date: Nov 1, 2005
By:  ORC STAFF
Source: Jeep at Off-Road.com

A Conversion to Chrysler ignition system using Mopar Performance Parts.

Parts Required:
  • P4120505 (Orange ECU)
  • P3690152 (Harness Kit)
Instructions:
  1. Mount ECU near old control unit (Do not remove or disable old unit).
  2. Disconnect distributor connector.
  3. Locate the purple striped and yellow striped wires and cut halfway back from distributor side of connector.
  4. Locate coil positive & negative and cut wires two inches back from coil.
  5. The following instructions describe how to splice the new harness connector to the vehicle wiring.
    1. Splice the br/wt wire to the bk/or wire at distributor conn.
    2. Splice the gy/bk wire to the pr/bk wire at distributor conn.
    3. Splice the bk/yl wire to coil negative wire (Tach Side)
    4. Splice the bl/yl wire to coil positive wire.
  6. Ign. timing:
    1. Disconnect and plug vacuum line from distributor.
    2. Start and set basic timing to 8 derees before top dead center.
    3. Locate ported vacuum. source at carburator (EGR line)
    4. Install a vacuum tee in this line.
    5. Route new line from this tee to the distributor vacuum advance unit.
  7. Carburator:
    1. Temporalily disconnect new harness from orange ECU.
    2. Reconnect original distributor connector and start vehicle.
    3. Remove air cleaner.
    4. Force engine lean by closing idle mixture screws till engine runs rough.
    5. At this point disconnect large mixture solenoid plug at back of carburator.
    6. Shut off engine.
    7. Disconnect original distributor connector and plug new harness back into orange ECU. Do not reconnect carb mixture solenoid.
    8. Start vehicle and reset idle mixture.
From this point on runPremium Unleaded Fuel ONLY.Tech Tip:
Old ignition system may be used in emergency by disconnecting harness from orange ECU and reconnecting original distributor connector. Trouble shoot:
 If vehicle won't run or runs poorly after first electrical set up try reversing the two splices at the distributor. This may occur because of wiring changes for different model years. Emissions:
 Electronic fuel control and afterstart idle up will no longer function after conversion. Color Conversion:
br/wt = brown/white striped
gy/bk = grey/black striped
bk/yl = black/yellow striped
bl/yl = blue/yellow striped
rd/gr = red/green striped
This coversion results in a dramatic improvement in throttle response, acceleration and top end power. Fuel economy effects are unknown at this time.

Note: For vehicles equipped with a dual vac. diaphram distributor it will be necessary to replace the diaphram with a single port type.This part may be obtained at your local dealer. Model year is not important as they are all user ajustable with an allen key inserted through the vac. port. Cost: Total cost for conversion assuming owner installation is less than $80.00. Comments:
This is most likely the best performance gain available for the least expense. This is an all around performance gain that can be felt in the seat of the pants.
Designed & Tested by:Craig Reynolds
Dayton Dodge
(908)329-3400
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Comments and questions from our Readers
Mike / dundalk, MD, UNITED STATES
 Posted Nov 24 2009 03:36PM
with the Conversion to Chrysler ignition system using Mopar Performance Parts can you also use the nutter bypass? thank you for your time. MIKE
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Source: Jeep at Off-Road.com, 11/1/2005
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