Wire Routing

Jeep Wrangler Nutter Bypass

I finally decided to do the Jeep Wrangler Nutter Bypass. I can tell you for me it was totally worth it. I am seeing better performance, and easier starts. I can actually use my 5th gear on the highway where it is generally flat even with my 33’s. I decided to create this post so it might help someone out. It can be confusing reading some of the posts by the techies that get into the fine details of the Jeep Wrangler Nutter Bypass. So here are some pictures and a description of the steps involved. This is just for the ignition bypass. I am not going into too many details regarding carburetor adjustments and the like.

Note: Your vehicle may vary slightly, due to Modifications, Different Carburetors etc.. Feel free to contact me and I will be happy to help if I can.

Jeep Wrangler Nutter Bypass Distributor WiresSo here is a photo of the Purple and Orange wires that you read about in most posts about the Jeep Wrangler Nutter Bypass. You do not have to do anything here. I am just showing you these wires so you can see where they are located. This is helpful if you want to use a multi-meter to check out the wires and make sure you have the correct pair.
Jeep Wrangler Nutter Bypass Wire RoutingNotice the twisted orange and purple wire.This is where they come out of the wire loom and go down through the firewall.

  • You will be cutting them just about where the arrow indicates.
  • Cut the orange wire and strip the end.
  • Cut the purple wire and strip the end.
  • Then cut two lengths of new wire that will reach from your splice to the ignition control module. The ICM is usually located behind the windshield washer tank on the firewall.
  • Attach your two new wires to the newly cut and stripped orange and purple wire.

Be sure that you are attaching the wires to the side that comes “FROM” the distributor, “NOT” the wires that go into the firewall.

Jeep Wrangler Nutter Bypass Ignition Control Module

  • Strip the other end of the wires that you just ran to the ICM
  • Cut the orange wire at the ICM Connector.
  • Strip the end of the orange wire.
  • Cut the purple wire at the ICM Connector.
  • Strip the end of the purple wire.
  • Attach the two wires that you extended earlier.
  • Orange to orange.
  • Purple to purple.
  • Put all your wires back into the loom and tidy up.

Adjust the Timing

  • Connect your timing light
  • Start the Engine
  • Warm up to operating temp
  • Turn off Engine
  • Loosen the distributor lock nut
  • Remove and plug the vacuum line from the distributor
  • Start Engine
  • Adjust for 8* BTDC
  • Stop engine
  • Tighten distributor lock nut
  • Start engine and check to make sure nothing moved
  • Replace Vacuum line to carb
  • Stop Engine

Jeep Wrangler Nutter Bypass – Additional Notes

  • You want your distributor’s vacuum line connected to ported vacuum not manifold vacuum (Off the carb, not the manifold)
  • Adjust your carb’s  idle mixture screws for the best lean running setting you can achieve
  • Don’t be confused by my photo showing the Ignition control module on the fender. I put it there. It was under the washer fluid reservoir  and it was hard to get to.

Disclaimer: The information provided is to be used by the reader at their own discretion. The author assumes no liability and cannot be held responsible for the misuse or improper interpretation of this information. This modification was performed successfully by the author using the above methods.

27 comments on “

  1. Wish I had checked out your info first could have saved a couple hrs figuring things out I wasn’t getting clear instruction on which end to splice new wires to thanks for the clear info and pictures how important is it for timing to be dead on and can I ditch most of the miles of vacuum lines I’d appreciate any info thanks. SZ

    1. You should use 8* BTDC as the starting reference point. Don’t forget to remove the vac line to the distributor and plug it while adjusting. +/- 2* is generally acceptable. You want the Engine running as smoothly as possible within that timing range. Don’t forget that when you are done you want the distributors vac line connected to the carbs vac port not the manifold.

  2. I just purchased a 88 yj 4.2l. It has what appears to be a new or reman. Bbd carb on it. There is no stepper motor though. Can i still do the nutter bypass?

    1. Yes, you can. There is actually a first step left out of my directions for carbs with stepper motors that bypasses the use of the stepper. So if you have an aftermarket carb without the stepper motor you only have to do the ignition part of the bypass described in my blog.

  3. This is not possible unless you have a 2.5 that was converted to a carb engine. Your Jeep is most likely fuel injected and the injectors need the ECM to control the injectors. The YJ 2.5L 1987-1995 engines were equipped with Fuel Injection from the factory. So unless yours was changed you cannot do the bypass.

    1. That is correct on some builds the Orange does change to a Green wire with a black stripe on the other end.
      Just to be sure, but you probably have done this already… meter it out. In the past I have found it is the same connection.

  4. I have a 84 dj5 2.5 done the nutter bypass but can’t figure out how to adjust the carburetor… It runs at a idle but won’t run when you give it gas???

    1. Was it behaving like this before the nutter bypass? If so it may be the accelerator pump. Look down the carburetor throat and work the linkage several times. You should get 2 squirts of fuel every time you work the linkage. If it just dribbles this is most likely the issue.
      Don’t forget You want your distributor’s vacuum line connected to ported vacuum not manifold vacuum (Off the carb, not the manifold)
      after you have done the bypass.

  5. My 89 4.2 with howell orange wire not connected to anything is this why im not running trying to chase down why injecters are not firing and found orange wire not connected to any thing

    1. You need 12v at the orange wire while cranking or running if it is not connected it may be your issue. I assume this is just a question regarding the orange wire in a fuel injected setup as you cannot do the Nutter bypass to a fuel injected system.

  6. Hello. I am wanting to do the nutter bypass on a 89 jeep wrangler yj.. But It would seem that I am missing another pig tail that should plug into the pig tail coming off the distributor. So,

    On a 89 Jeep Wrangler, Where do the orange,black and purple wires go to after they come off the distributor. It seems as though there should be another pig tail that plugs into the distributor wires and ….where do these tie into the harness and do they change into a different color along the way. WHERE do they go after they leave the distributor?
    Any help would be much appreciated.
    Thank you.
    Jerry

    1. Jerry,
      The orange and purple wires leave the distributor and go into the harness as shown in my photos. Normally at about the center of the harness along the firewall the harness “T’s” down the orange and purple normally go down the “T”. You will be cutting the orange and purple wire at that point or anywhere before that point. The orange and purple wires from the distributor side where you cut will be extended to your Ignition Control Module (Usually located behind the windshield washer tank. Cut the purple and orange wire on the ICM side and attach to the wires that you extended from the distributor. Hope this helps. Is there anything I can do to help my posts instructions ?

  7. I need to ask you a question concerning this modification. When I cut the wires at the ICM, do I connect the distributor wires to the wires incoming to the ICM or are they connected to the outgoing wires of the ICM?

    1. Richard,
      I don’t know if you can see my response to Jerry below but it seems like the same question.
      The purple and orange wire on the ICM get connected to the extended wires from the distributor
      that you cut into at the firewall.

      Here is my response to Jerry…
      In reply to Jerry.
      Jerry,
      The orange and purple wires leave the distributor and go into the harness as shown in my photos. Normally at about the center of the harness along the firewall the harness “T’s” down the orange and purple normally go down the “T”. You will be cutting the orange and purple wire at that point or anywhere before that point. The orange and purple wires from the distributor side where you cut will be extended to your Ignition Control Module (Usually located behind the windshield washer tank. Cut the purple and orange wire on the ICM side and attach to the wires that you extended from the distributor. Hope this helps. Is there anything I can do to help my posts instructions ?

  8. 1990 Wrangler YJ 4.2L, basic- recently purchased and runs real bad- lack of power, seems vacuum related. It has an aftermarket Carter carb and vacuum lines all over the place. The Nutter Bypass and retiming hasn’t been done yet. I will do that first though I know there are vacuum issues. Does anyone have a procedure, photos or idea of what vacuum is essential? The to/from connections would be ideal. I can’t wait to get rid of all that mess under the hood. Thanks

    1. I may be posting something that will help you soon. For now the short answer is you need your Brake Vacuum booster line, your PCV line the vacuum line to the distributor but you want your distributor’s vacuum line connected to ported vacuum not manifold vacuum (Off the carb, not the manifold). If you have not changed the front axle lock to a cable system it is vacuum controlled you will need that vacuum line. Hope I did not miss anything. I will do a more complete write up with pictures. I got rid of all the emissions crap. Got better gas mileage and performance.

  9. Thanks for the great instructions! I have an 83 scrambler that I have recently Nuttered. Since doing so, it has been running good, but it’s very hard to start. If I switch it back, it fires right up, but don’t run as good, so I pulled the main wire from distributor cap, grounded a spark plug to the block and plugged it in. With the Nuttered wiring, I only get one spark at the end of cranking. If I switch it back, I get all kinds of Sparks. I have checked my wires over and over, and I am pretty sure it is right. Orange and purple from distributor to orange and purple at the ignition module. Any ideas what I could be doing wrong? Thanks.

  10. Thanks for the work that you do and posting it. I have a 1981 CJ8 that I want to put a Weber carb on does the nutter bypass still have to be done on this year Jeep?

    1. Technically his modification is not legal for EPA regulated U.S. street vehicles. However I have used the mod on most of the jeeps that I have owned. You do not HAVE to do the bypass, it is a mod to improve operation and performance. This modification will do two things. It will rewire the ignition wiring like an ’78 to ’82 CJ with the 258 engine, that does not have the Carter BBD carburetor.(like your replacement carb) It will make the stock carburetor with its computer controlled stepper motor work with the rewired ignition. I would suggest a motorcraft over the weber. Both are good carbs but the weber is harder to tune.

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