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How to - Nutter Bypass

414K views 505 replies 176 participants last post by  KDub1984CJ7 
#1 · (Edited by Moderator)
Ok, for all those who want to perform the Nutter Bypass to eliminate the Electronic Control Module from your '83 and later CJs and YJ's with 4.2L engines & BBD carb, here's the how to.

I know I had a lot of questions before doing it about how to, etc., and I've seen a lot of others asking questions, so I figured why not create this so that, hopefully, most questions are answered. A little preparation on the front end saves a lot of headaches on the back end, right?

This is NOT a 'why should it be done post? For that, you should do other searches and then come back to this if you decide to do it.

It's easy to do, and it did benefit me. I no longer have the rough idle, including my Jeep's 'cough' during idle. My gas mileage prior to the bypass was 16.2mpg. After filling it up and emptying a tank, it was at 18.7mpg. That was with a lot of stop and go and even a little mudding.

Also, a BIG THANKS!! goes to Mike Romain, who read over, corrected, and helped a lot with this write up. :cheers2:

So without further ado, here it goes. Step by step (with pictures!!). :2thumbsup:

Stepper Motor Needle adjustment: Steps 1 & 2

Step 1: Adjust the stepper motor needles in the carb so that the shoulder sticks 1/8" into the carb.

Stock stepper pins run in the middle of their travel which is when their shoulder is 1/8" to 1/4" away from the carb wall (closer to 1/8" is preferable). Several people have set their pins at this level and have reported improved results over the 'full rich' setting in John Nutter's original setup. Some of these jeeps have also passed emissions testing with the needles set in this position. Of course, it's a Jeep thing, and your results may vary.

To get your stepper pins the way you want them, the easiest way would be to remove the stepper motor from the back of the carb and adjust the pins, then re-insert and affix the motor to the carb. Ensure you did not move the pins when re-inserting the motor.

Another option is to adjust your idle mixture screws on the front of the carb while the engine is running: Out (counter-clockwise) - to have the stepper pins move into the carb and create a full, rich condition, or In (clockwise) - to have the pins move into the stepper motor to create a more lean condition.

Step 2: If you choose to adjust the stepper pins using the idle mixture screws method, once the stepper pins are at the level you choose, turn the ignition off and unplug the electrical box from the back of the stepper motor (remains unplugged forevermore).



Re-routing wiring: Steps 3-11

Here is a link to a diagram of before and after wiring... Blog | Earthlink

Step 3: Find the orange and purple wires at the distributor.



Step 4: Follow the wires through the wire loom to where they enter the firewall (it may be necessary to remove the loom).

Note (Read prior to Step 5): It is sometimes recommended that you do not cut into the wires inside the loom. Rather, add two new twisted wires for the full length. One reason is YJ 258's have different color codes in the harness than CJ's. This will also leave it as close to the original as possible so future owners, or you, may change it back if this is desired. In this case, you could add two new twisted wires from the Ignition Module end to the Distributor end.

I did not do it this way. I went ahead and cut the wires at the firewall. If you prefer to do it the way I did, follow ahead. If not, perform the following steps by adding new wires end to end.

Step 5: Cut wires 3"-4" from the firewall. I brushed my unused ends with 3m electrical coating, then wrapped them in electrical tape just because I felt better about it rather than just leaving them exposed.

Step 6: Find the orange and purple wires at the ignition module (under the washer fluid reservoir). I had to remove my washer fluid and overflow reservoirs to get to the module.



Step 7: Cut the wires at the ignition module. I protected the unused ends here the same way as in step 4.

Step 8: Cut two lengths of extra 16 gauge wire to reach from ignition module to the firewall where you cut wires in step 4. Or to the distributor if you chose that method. Hint: If using the same color wire, mark each end of one as 'purple' and the other as 'orange'. Or, do as I did and simply color both ends of one wire, so you know which wire goes to which color once they have been twisted.

Step 9: Twist the two lengths of extra 16 gauge wire together just as the stock orange and purple wires are twisted. (This helps with insulation from outside electrical interferences). Hint: I read this trick elsewhere, and it really helped. Put one end of the wires in a 'C' clamp or something similar and the other end of the wires in an electric drill. Then twist. This made the process a lot easier. Twist until you meet about the same coil as the stock wires.

Step 10: Attach your extra 16 gauge wire from the orange at the ignition module to the orange from the distributor.

Step 11: Attach your other extra length of 16 gauge wire from purple at the ignition module to purple from the distributor.



Vacuum hose move. Steps 12-13

Step 12: At the carburetor, remove the vacuum line that is currently going to the distributor and plug the outlet you just removed it from.



Step 13: Find the ported vacuum line just behind the choke coil on the valve cover side of the carb and remove this line. Using a 'T', attach the distributor vacuum line to the other vacuum line you just removed.



Adjust timing to 8* BTDC. Steps 14-25

Step 14: Warm up the engine to operating temperature, then shut it down.

Step 15: Unplug the vacuum line at the distributor and plug it in.

Step 16: If using a timing light, follow the instructions to hook it up. Should be like this: Clamp the pickup onto the #1 plug wire, then hook up the negative lead to the negative side of the battery, then the positive to positive on the battery. Ensure no wires are in the way of fans, belts, or hot engine parts.

Step 17: Locate the timing marks on the front driver's side of the engine. The lowest mark is -2 degrees. You want the timing to be at the 6th markup. Each timing mark equals +2 degrees, counting up from the bottom.



Step 18: Loosen the bolt, which is below the distributor on the right hand side, slightly so you will be able to rotate the whole distributor.



Step 19: Start the vehicle.

Step 20: Take the timing light and aim it at the pulley to the left of the timing marks you found earlier. When the light flashes, you will see the notch in the pulley. You want it to be at 8* BTDC (+/- 2*). Check the timing marks on the front of your engine; however, on all in-line six cylinder engines, it should be the 6th markup.

To advance the timing move the ENTIRE distributor counter-clockwise. To retard the timing, go clockwise. DO NOT move the distributor by holding at the top. Move it from the bottom. You could get shocked otherwise.

Step 21: Turn the engine off.

Step 22: Lock the distributor in place by tightening the ½" bolt.

Step 23: Start the vehicle and re-check the timing. If it is of any, follow steps 18 through 22 again until it is right.

Step 24: Turn the engine off and clean up your mess, be sure to replace the vacuum hose you removed in step 15.

Step 25: Adjust the idle mixture screws on the front of the carb to the 'best lean' idle mixture and re-tune your carb.

Step 26: Enjoy a great running Jeep!!

Next for me...TEAM RUSH!!
 
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#353 ·
By putting it back to the way it was supposed to be wired ? , 2 of the 4 are spliced to bypass the MCU the other 2 just travel the harness , I've never had trouble with the Dura Spark system unless some FBN part has been replaced by a Parts Changer - A Mechanic figgures out what's wrong and doesn't just throw parts in till it runs .
 
#354 ·
1949er said:
By putting it back to the way it was supposed to be wired ? , 2 of the 4 are spliced to bypass the MCU the other 2 just travel the harness , I've never had trouble with the Dura Spark system unless some FBN part has been replaced by a Parts Changer - A Mechanic figgures out what's wrong and doesn't just throw parts in till it runs .
Trust me I'm a mechanic. I don't throw parts.

Everything I do had to be bullet proof. If it isn't I would get a call from Grammy telling me her jeep won't or wouldn't start. Any mod I wanted to do had to work flawlessly by Monday morning.

I paralleled the orange and purple wires coming from the distributor and ran them to my MSD. I could probably remove the two vacuum switches (load sensing for timing) and two of the three vacuum solenoids the upstream and down stream air injection pumps) on the valve cover. But I didn't.

In my opinion the BBD and the MCU does a good job of controlling the fuel. The spark side to me had a lot to be desired.

I would drive it to California now, I trust it so much. In the beginning (I met my wife in 1998 and assumed the duties of CJ maintenance) not so much.
 
#355 ·
Well as a Retired Mechanic after working in pretty much all fields of repair for 45 yrs. when you take a controled unit and remove just one of many sensors or controling factors it can and will have an effect on the entire system , the computer controled BBD was a futile attempt to control smog even tho AMC had MPI on the 4.0 , the combustion chamber of the 258 is the main culprit as it is not efficent , the 4.0 is better and in conjunction with the MPI it does well , It seems to me if you take a carb and put a motor on it that is controled by several different components with ware factors as well as age and climate change it spells trouble , I'm building a non-stepper carter ( not much better ) for this motor and if it doesn't work it will get a Rochester 2gc.
 
#356 ·
It's been like this for long enough to know there are no issues with it.

When I had the stepper centered and unplugged the AF was ok below 40mph and lean above. Raising the needles to fatten up the AF above 40mph made it too rich for my liking below 40mph. So I hooked the stepper back up and woke up the MCU.

A few years later when I rebushed the baseplate I put my Fluke DVM on average and drove it around 8 miles and the times I recorded the averaging it averaged .49 to .51. Which is as good as any FI would do. I have at least 1 or two YouTube videos to prove it.

The needles out of a non-stepper probably would have had a better profile and solved my problem. However, I used the MCU and liked my results.
 
#357 · (Edited)
New to me 84 CJ. I am in an EMISSIONS zone. Working on finding out if the pulse air works and was wondering if "Nuttering" would affect anything. This is a CA Jeep, though I live in Las Vegas. They check to make sure components are there (CAT, PUMP (should be fun to explain the pulse air), and fuel restrictor) and then tail the emissions. I am getting a new exhaust/cat since I do not trust a rusty 30 yr old unit. I was planing on doing the Nutter and Rush upgrades. Any feedback would be great. I prefer to eliminate the computer and ... in the future, maybe do a junkyard TBI.
 
#360 ·
New to me 84 CJ. I am in an EMISSIONS zone. Any feedback would be great.
How about registering as a "Classic Vehicle" and being exempt from emissions testing?

Vehicles registered with Classic Vehicle, Classic Rod or Old Timer license plates and driven 5,000 miles or less per year are exempt from emissions testing.

http://www.dmvnv.com/emission.htm#Classic
NRS 482.3816
A Nevada resident who owns a passenger car or light commercial vehicle (having a manufacturer's rated carrying capacity of 1 ton or less), manufactured at least 25 years prior to the date of application, may apply for Classic Vehicle license plates

http://www.dmvnv.com/pdfforms/sp34.pdf
 
#363 ·
On step 13, where does each liinr from the "t" connect? I know it comes from the distributor, then connects to the carb on the passenger side halfway on the carb. But where does the other line connect? Sorry if this has been answered. I'm doing this bypass on a carb that had no lines attached in the first place, it's cold here in GA so a quick reply would be much appreciated. Edit: and also where does the line from step 12 go? Pictures would help alot
 
#365 ·
I'm a bit of a newb here but have read everything and every link coming off this thread on the subject.


Background:

I just recently picked up a 1984 cj7 with the 258 i6 in it. I'm told the carb on it is a webber. It looks to me like almost all of the smog stuff is ripped out as I have wires just hanging all over the place. I had noticing that I'm unable to really get going up on the highway and that it slows down really bad going up hills at speed. 3'rd gear is about the high end that I can use unless on very flat ground. I have been having stalling issues where it stalls at idle from time to time and sometimes when shifting in the first or second gear.

I was thinking that this (nuttering) might be a necessity to help make it run a little better. So here is what I noticed:

It looks like the nuttering job was already (poorly) performed on the beast, It also looks like there is some form of after market ignition module that is mounted directly above the block on the firewall (I'm making this guess because the purple and orange wires from the distributor are spliced and going up to that) so I assume the stock is just hooked up to the harness but not being used.

To validate that the nutter job was done, I disconnected the computer (under dash) from the plug on the harness on it's rear allowing me to pull it out completely.

Questions:

The rig still fires up after computer removal and seems to run like it did before (just as crummy) so am I correct in assuming that it's been nuttered? :confused: Also, my ignition key cylinder just kind of stopped working and turns really loose or locks the steering wheel, so I use the key to unlock the steering wheel but to start it I currently have it on a two (one for the starter the other for the "on" phase of the jeep) toggle switch system that I just wired from the (two) plugs that connect under dash to a small rectangular box mounted up by the rear of the column, would this effect anything?

Second, I was trying to decipher all the vacuum hose issues and to see if that was done correctly but I do not know which webber carb I have. Is there an easy way to determine what model it is? I think it's running rich because I feel there is excess fuel smell (I think this is an indicator of running rich)... Is this correct?

Should I stop worrying about the vacuum lines and wiring for now and simply remove all the extra garbage from the computer harness then see whats left after the excess junk is removed and try going from there to get the vacuum lines / carb tuned / timing done? What exactly is the best place to start?

Another question I have is that I thought after being nuttered there shouldn't be any wires as all going to the carb? I have a single black wire coming out the (driver) side of the carb and if I pull that wire while the jeep is running it will stall unless I give it some gas or crank the hell out of the idle screw, Is this supposed to be there or is something wrong because that wire needs hooked up?

I'm in a smog check zone but there is no way this thing will smog right now since it doesn't even have a cat so I can't pass the visual by any means- I have it on a temp and will register it in a no smog check zone since I can't register it as a classic because I breach the yearly mileage limit- So at this point I will not worry about having to pass smog checks, I'm more worried about trying to get it running smoothly and to perform well.

Any assistance/advice would be helpful, and I hope I'm on the right track with trying to resolve this nutter job issue first and removing all the excess stuff before moving on to try to fix what's left.
 
#367 ·
I Questions:

The rig still fires up after computer removal and seems to run like it did before (just as crummy) so am I correct in assuming that it's been nuttered?
Yes

Also, my ignition key cylinder just kind of stopped working and turns really loose or locks the steering wheel, so I use the key to unlock the steering wheel but to start it I currently have it on a two (one for the starter the other for the "on" phase of the jeep) toggle switch system that I just wired from the (two) plugs that connect under dash to a small rectangular box mounted up by the rear of the column, would this effect anything?
If your switch system starts the engine and keeps it running, then I doubt that's your problem

Second, I was trying to decipher all the vacuum hose issues and to see if that was done correctly but I do not know which webber carb I have. Is there an easy way to determine what model it is? I think it's running rich because I feel there is excess fuel smell (I think this is an indicator of running rich)... Is this correct?
Post a pic of the carb, and one of us can ID it for you. The fuel smell can be from improper carb tuning (ie: Air/fuel mixture), choke not opening, lack of a vapor canister, or a leak.

Should I stop worrying about the vacuum lines and wiring for now and simply remove all the extra garbage from the computer harness then see whats left after the excess junk is removed and try going from there to get the vacuum lines / carb tuned / timing done? What exactly is the best place to start?
As Mike said, I'd leave it for now, and get it running well, first. Then, if you want to clean up the engine compartment, remove components and wires one at a time, and confirm you haven't messed anything up after each removal.

As for tuning, start with checking for vacuum leaks. Once you're convinced there are no leaks, set the timing, then tune the carb.

Another question I have is that I thought after being nuttered there shouldn't be any wires as all going to the carb? I have a single black wire coming out the (driver) side of the carb and if I pull that wire while the jeep is running it will stall unless I give it some gas or crank the hell out of the idle screw, Is this supposed to be there or is something wrong because that wire needs hooked up?
Does the wire connect to a round black thing? If so, that's you're electric choke. A pic would help here, also.

Any assistance/advice would be helpful, and I hope I'm on the right track with trying to resolve this nutter job issue first and removing all the excess stuff before moving on to try to fix what's left.
Again, leave all that stuff for now. Poke around this site and determine which systems you have, and if they are operational.

Good luck, and remember, the only dumb question is the one you don't ask. :thumbsup:

Matt
 
#366 ·
You are correct that it has the computer bypassed But I do not recommend you tear anything out until you find out what is wrong with it. Make it run first!
 
#368 ·
Thank you both for the advice- I will take it! I should probably start up a new thread for my own issues to not further clog this one as it looks like I will be dealing with many other things as well. I will get some pics either later tonight or in the morning and see what trouble I can't get into :) Thanks for the link- I have bookmarked it and will go through the process of cataloging what I have and then get the carb ID'd, vacuum system checked and while I'm at it the fuel filter etc. then move on to timing and then carb tuning.
 
#370 ·
am I correct to presume that the nutter also can apply to a 4 cylinder engine? I have an '84 and will be pulling the body soon (hopefully) and would like to take clean up my engine bay when I put the body back down. I will also be installing a new painless harness so I should have nice new wires to cut.

thanks.
 
#371 ·
am I correct to presume that the nutter also can apply to a 4 cylinder engine? I have an '84 and will be pulling the body soon (hopefully) and would like to take clean up my engine bay when I put the body back down. I will also be installing a new painless harness so I should have nice new wires to cut.

thanks.
Yes and painless doesn't come with any ignition wires, not even the ballast resistor according to another poster today so don't throw everything out until you are done.
 
#374 ·
Hi guys. I am currently doing this on my 84 I4 150. I have a couple questions. I see the three wires coming off the distributor, orange, purple and black. I am taking the whole harness out, so what does the black wire go to? I am assuming ground, but I learned never to assume. Also, on the other end. I see an orange, green and black wires coming off the icm, but the purple wire is dead ended in the plug? Do I cut the purple wire out of the plug and splice it to the purple off the distributor. If that's the case what does the green and black wires get hooked too. I am trying to leave the harness 100% in tacked so someday (i doubt it) it can be put back to original. I am using plugs and what not off another 86 i have sitting in the garage. It will have a 351w so i don't need all that wiring crap.
 
#375 ·
Black goes to black. It is the ground and uses the distributor hold down foot for the ground path. You can add a dedicated battery ground to this for a better connection to ground. Purple at ICM gets cut and spliced. Green is the coil negative trigger wire.

Be sure you twist the new wires together that feed the orange and purples for RF.
 
#376 ·
Ok, since I am taking the whole harness out. The black, orange, and purple on the distributor can be spliced to the black, orange and Purple on the ICM. The green from the ICM needs to be spliced into the trigger wire at the coil?
Why do the wires need to be twisted together?

Thanks sorry for the newbie questions. Been several years since I have really messed with the cj's.
 
#377 ·
Ok, since I am taking the whole harness out. The black, orange, and purple on the distributor can be spliced to the black, orange and Purple on the ICM. The green from the ICM needs to be spliced into the trigger wire at the coil?
Why do the wires need to be twisted together?

Thanks sorry for the newbie questions. Been several years since I have really messed with the cj's.
The green is the coil negative wire. This controls when the coil fires.

You twist the orange and purple wires together so radio frequency (RF) emissions don't interfere with the pulses in the wires. Radios, alternators, spark plugs, cell telephones, all these things can send out radio waves that could interfere with a clean ignition signal and cause a miss in the engine.

I used insulated type SOW cable (commonly called 'cab tire' cable, covers anything) on a lot of them for this reason. The SOW wire has twisted wires inside with a paper and silk thread capacitor wrapped with them. All for RF insulation. Probably overkill, but I had the wire on hand from installing mobile data computers in delivery vehicles that were real touchy about RF.

Stock, AMC just twisted them, no issues.
 
#379 ·
Not unless you want to. None of the emissions things will work except the gas tank vent ( canister), PCV and EGR but they can be left in place.
 
#381 ·
Notches are 2° starting with +2 on the far right. Don't know the base timing for a 150, sorry.
 
#382 ·
What happened to my nutter

I have tried the nutter twice and still haven't got it right. When it comes time to set the timing I start the engine and it will only run for 3 manye 4 seconds then it just dies. No way I can keep it running long enough to time it. What am I doing wrong?
 
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