OBD1 XJ 4.0 swap - fuel pump ballast resistor bypass relay removal - JeepForum.com
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Unread 03-03-2014, 10:10 PM   #1
JeepScrambler
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1985 CJ8 
 
Join Date: Nov 2004
Location: Claflin, KS / Houston, TX
Posts: 139
Finally finished my junkyard 4.0 MPFI head swap a few months ago on my '85 CJ7 so I'm back to working on one of my '84 Ak postal scramblers that is getting an OBD1 4.0 AW4 swapped in. Since I eliminated the PDC in my '85 CJ7 head swap many of my notes I had made don't apply to well to my current wiring dilemma. I have most of the wiring done, the jeep cranks over fine and has spark at the plugs. My engine and transmission are from a '95 Cherokee and the wiring harness is from an earlier '92. The earlier XJs (91-93 I believe) have a ballast resistor bypass relay to drop the voltage to keep the pump somewhat quieter. The later OBD1 XJs did not have this.

In an attempt to clean up even more wiring under the hood I am wanting to eliminate the ballast resistor bypass relay and it's wiring entirely. A question I have about doing this is one of the two green w/ black tracer wires running from the 30 pin on the ballast resistor bypass relay goes to the heated O2 sensor. The other green w/ black tracer wire from this bypass relay is connected back to the fuel pump relay. What purpose does the green w/ black tracer wire going to the O2 sensor serve? Can the wire just be cut from the O2 sensor plug or does it need to be connected back to the fuel pump relay now that the ballast resistor bypass relay has been removed?

I have attached a few pictures of the plugs and the wires I am referring to. There is also a red w/ purple tracer wire that is a smaller gauge running from this bypass relay to pin 37 of the PCM. My pin outs are all for '95 XJs so I'm not sure what this wire does. I plan to just cut this wire near the PCM. The last wire in question is a blue w/ white tracer wire running to a factory splice that connects several other blue w/ white tracer wires. I just plan on cutting this at the splice to eliminate it from the wiring circuit. Has anyone out there who has done this swap or is running an XJ that has eliminated it please let me know what you have done with these wires, particularly the green w/ black tracer running from the ballast resistor bypass relay to the heated O2 sensor. Thanks for the help!

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'06 Grand Cherokee "Overland"
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Unread 03-04-2014, 12:36 PM   #2
SLO_Ken
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1986 CJ7 
 
Join Date: Nov 2009
Location: California
Posts: 856
Quote:
Originally Posted by JeepScrambler View Post
In an attempt to clean up even more wiring under the hood I am wanting to eliminate the ballast resistor bypass relay and it's wiring entirely. A question I have about doing this is one of the two green w/ black tracer wires running from the 30 pin on the ballast resistor bypass relay goes to the heated O2 sensor. The other green w/ black tracer wire from this bypass relay is connected back to the fuel pump relay. What purpose does the green w/ black tracer wire going to the O2 sensor serve? Can the wire just be cut from the O2 sensor plug or does it need to be connected back to the fuel pump relay now that the ballast resistor bypass relay has been removed?
These two should stay connected. The wire that goes to the O2 sensor is for the O2 sensor heater circuit. The sensor will not operate correctly without it.


Quote:
There is also a red w/ purple tracer wire that is a smaller gauge running from this bypass relay to pin 37 of the PCM. My pin outs are all for '95 XJs so I'm not sure what this wire does. I plan to just cut this wire near the PCM. The last wire in question is a blue w/ white tracer wire running to a factory splice that connects several other blue w/ white tracer wires. I just plan on cutting this at the splice to eliminate it from the wiring circuit. Has anyone out there who has done this swap or is running an XJ that has eliminated it please let me know what you have done with these wires, particularly the green w/ black tracer running from the ballast resistor bypass relay to the heated O2 sensor. Thanks for the help!
Yes, you should be fine doing it this way. The bl/wt is the ignition feed to the relay. The rd/ppl is the switched ground to activate the relay.
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Unread 03-04-2014, 06:33 PM   #3
JeepScrambler
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Join Date: Nov 2004
Location: Claflin, KS / Houston, TX
Posts: 139
SLO_ken, thanks for the replay. I have been speaking with Thisguyyouknow on the forum as well about this. Basically what has been concluded is I can connect the green w/ black tracer from the O2 sensor and run it back to the fuel pump relay to the same pin that connects to the fuel pump power supply wire(need to get the exact pin number that connects to the relay when I get back home). The O2 sensor and fuel pump will both get continuous 12 volts in this configuration now. Whereas before, the fuel pump voltage would drop because of the ballast but the O2 sensor would always get a constant 12 volts.

Thisguyyouknow and I were discussing the red w/ dark blue tracer wire running from pin 37 on the ECM to the ballast resistor bypass relay. I was considering just cutting this wire and not using it but there was some concern with the ECM not getting a signal/ground from the relay and throwing a check engine code. He suggested splicing the pin 37 red w/ dark blue tracer wire (pin 86 on the ballast resistor bypass relay) wire from the ECM to the blue w/ white tracer wire (pin 85 from the ballast resistor bypass relay) to give the ECM the full signal just in case.

Being that the 94-95 XJs has pin 37 on the ECM empty I'm not sure if this wire is even necessary to hook up? Could I get away with just cutting the wire and leaving it disconnected, get a 94-95 ECM, or just make the splice and call it done? I would ideally just like to cut the wire and remove it all from the harness. Anyone know for sure if this will work or could I get a possible check engine code of the wire isn't connected?
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1985 CJ8, '85 CJ8, '85 CJ7, '84 CJ7, '84 CJ8, 2-'84 CJ8 AK Postal Scramblers, '82 CJ8, '82 CJ8, '82 CJ8, '53 CJ3A
'02 Dodge Ram 2500 4x4 Cummins HO 6 spd
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'06 Grand Cherokee "Overland"
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Unread 03-04-2014, 07:24 PM   #4
SLO_Ken
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1986 CJ7 
 
Join Date: Nov 2009
Location: California
Posts: 856
Quote:
Basically what has been concluded is I can connect the green w/ black tracer from the O2 sensor and run it back to the fuel pump relay to the same pin that connects to the fuel pump power supply wire(need to get the exact pin number that connects to the relay when I get back home). The O2 sensor and fuel pump will both get continuous 12 volts in this configuration now. Whereas before, the fuel pump voltage would drop because of the ballast but the O2 sensor would always get a constant 12 volts.
Exactly correct.

Quote:
Thisguyyouknow and I were discussing the red w/ dark blue tracer wire running from pin 37 on the ECM to the ballast resistor bypass relay. I was considering just cutting this wire and not using it but there was some concern with the ECM not getting a signal/ground from the relay and throwing a check engine code. He suggested splicing the pin 37 red w/ dark blue tracer wire (pin 86 on the ballast resistor bypass relay) wire from the ECM to the blue w/ white tracer wire (pin 85 from the ballast resistor bypass relay) to give the ECM the full signal just in case.
Pin 37 is just a switched ground in the ECM. If you splice the bl/wt (ignition feed) to the rd/bl, you will be creating a dead short through the ECM... not an ideal setup!

Quote:
I would ideally just like to cut the wire and remove it all from the harness. Anyone know for sure if this will work or could I get a possible check engine code of the wire isn't connected?
Yes, this should work. There is no check engine code that I am aware of for the ballast resistor.
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Unread 03-04-2014, 07:56 PM   #5
ThisGuyUKnow
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Join Date: Jul 2008
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I think you will be fine leaving pin 37 open.
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