[Guest]

I have the 258 with tons of smog crap and whatnot in my 1988 AMC Eagle. The engine compartment looks exactly the same as my 1987 Jeep Wrangler. I've been having problems getting the thing to run right, and I've come to the conclusion that I need to fix things with this nutter bypass and possibly a new carb. I have a couple of basic questions because I'm not sure exactly what the nutter will be doing.

1. I see a lot of people that have listed in their Jeep info -both- a new carb and the nutter bypass. Why would I need to do both? As I understand it, the computer controlled BS resides on the carb itself, so if that is all replaced, why would you need to do both?

2. Apparently the nutter instructions have been removed from their original site. I had some printouts of it but my brother gave them away when he sold his old Cherokee! So, I ran a search on this forum and found two helpful sites, one with instructions, and a separate one with wiring diagrams. The one with instructions talks about a new ECU - What is an ECU and why do I need a new one? I also haven't found one that tells (step by step for a beginner [like me] how to put the carb in full rich position [which as I understand it, is required to get it to work right]). Is there a place that mirrors the original article or has all the information, theory, and diagrams all in one place (preferably with pictures)?

I am a web developer by trade so if anyone has pictures or a write-up that they would like posted permanently on the web, please e-mail them to me and I will post them up for you (my search for "nutter bypass" found tons of people asking the same question and all being pointed to the same articles which don't seem to be as detailed or informative as the original).

3. When I start the engine, it appears that the lever thing on the distributer gets pulled instantly and stays that way. I'm having a severe pinging problem and gone through all the regular hoops to try to find it. I've done a compression test [all normal], replaced EGR, replaced distributor, timed it, replaced wires/plugs, distributor cap, rotor, etc, ran 3 tanks worth of high octane gas, tried various carbon-removing products that you put with your gas, etc. It seems like the distributor is being pulled at full advance all the time (although I can't say for sure because I don't know which direction is advanced and which is retarded). The guy that had this before me said it's a new carb. We've adjusted it to the book specs and also by ear and we can't get the pinging to go away no matter *what* we do. I wanted to get a new carb but my brother suggests (after reading the nutter articles that I printed) we try the nutter before I spend the money and time on a new carb. Would bypassing the assumed defective computer system perhaps help this problem? I'm seriously about to give up, I've never had a pinging problem so stubborn, it was always something very simple. This one seems to ping less when it's cold, but that could be my imagination (and it still does it when cold), but when warmed up, it pings really bad. Basically, any time I accelerate (even from say 40-45 mph), any time I go up a hill, and any time I go over about 50 miles per hour. I can get it to run about 50 without pinging, as long as I don't hit an incline or let it drop down a few mph (which causes me to have to give it a bit more gas and PING again).

I've taken it to a local mechanic who confirmed that it was "pinging" and also said he double-checked all our work and confirmed that we did everything right - but also said that he had no idea how to fix it since we did everything he would have done.

Any help would be greatly appreciated!

 

[Guest]

Sound to me like you may have the vacuum advance line from the distributor hooked to a constant vaccuum source. I will check this evening and see what I have mine hooked up to. I went through this stuff a while ago trying to get my yj to pass emissions.
The vac advance lever should move when you accelerate. If the advance lever is moving immediately it will run rough. If your timing is a little off as well I should think that it would cause pinging as well.
Make sure the vac line to the distributor is hooked or tee'd into a port on the carb above the throttle body. If you are not sure just disconnect and plug the line right at the distributor. If it runs better at idle that is a start. Then you have to hook it up to the right vac source. I would then (at idle) check the timing (you need to buy or borrow a timing light). You can find the info for the rpm and timing marks in a manual or on this site. Hope this helps. Also, these engines are all but impossible to tune cold. Let the engine warm up completely before doing any thing.

 

[Guest]

Thanks for your reply. I should mention that it idles *perfectly* warm or cold, the engine runs smooth as silk at idle. We have done the timing according to the specs in my book (yes using a timing light). The timing was also verified by a mechanic.

 

[Guest]

I just don't get why the distributor is advancing immediately. If the timing is correct and the distributor is in the advanced position, when you accelerate the timing would start to go off because the system can't "advance" any more. That is (to my limited understanding) the whole purpose of the vacuum advance system. Just trying to help.

Also you can put the carb in a full rich position by adjusting the needle screws in the front of the carb to add more fuel or just closing the choke plate. The needle screws are touchy to get the carb back to a good idle. When you see the piston at the stepper motor move to the desire location you can unplug the motor for the nutter bypass. I can't remember which way, in relation to the vehicle it should move. If you close the choke by hand you should (no vac leaks) get a rich mixture and see the piston move to correct.

Hope I helped a little.

 

[Guest]

And that's why I'm going to such extreme measures. We can't figure wth is wrong with it. It is on ported vacuum (tested with a vacuum guage). That's part of my question, in which position is "fully advanced" vs. "fully retarded?" Because as soon as the engine is turned on, it moves. I'm wondering if that's the way it should be, perhaps I'm barking up the wrong tree. Is the lever deal closest to full advance when the car is turned off, or is it the opposite side?

Also, any info on the nutter questions? If I replace the entire carb, do I still have to do something with the nutter to make everything work correctly?

 

[Guest]

I will take a look at the position of the lever and orientation tonight and post what I find. Maybe the sound you hear is pointing to a different problem. Valves?

As for the "nuttering" of the carb, I have not done it myself. I researched it and I may have some instructions for the wiring. I will send them if I have them. The only reason I think that people do both is to squeeze some more power of the engine but still be able to put the stepper motor back into service later to pass emissions. If you put a new carb on, everything should work fine.

 

[Guest]

Does the carb run OK? Most people that do the Nutter bypass do so for the ignition side of the engine. The trouble you are having now. When timed to factory specs, the ignition is too far advanced and the computer retards as necessary with the help of vacuum switches and a knock sensor. The bypass takes the computer clear out of the loop. You will then need to find a ported vacuum line and retime to pre-computer specs. If you plug that vacuum line in, and the advance moves on the distributor, you are not using ported vacuum. Remember, the distributor gets manifold vacuum and the computer retards as necessary. Obviously, something is not working, and it is not retarding the distributor like it should. Hence the reason for the Nutter bypass. Hope this helps.

 

[Guest]

Well, we tested with a vacuum guage and it *is* ported vacuum, maybe there's too much vacuum for some reason?

 

[Guest]

With the engine idle at about 650 RPM, you will have very little if any vacuum. As you raise RPM, ported vacuum will also raise. Here is a web page that shows the ported vacuum:
http://home.sprynet.com/%7Edale02/vac-mcu.htm As you can see, very little of all those vacuum lines are ported. But you can see where to get ported vacuum off of the carb. But, then again, you will need to perform the Nutter Bypass before you go hooking up ported vacuum to the distributor. The computer is still trying to control timing through the electronic part of the distributor. Hope this helps.

 

[Guest]

Okay, Okay, maybe we are getting somewhere. Are you implying that I should not have ported vacuum going to my distributor NOW? I have done no modifications yet, everything is stock. I think there is ported vacuum to the distributor now. Should that be full manifold vacuum?

EDIT:

Okay, I'm supposed to have full vacuum going to the distributor, I misread your posts, but now I am clear. In the stock configuration, I should have full vacuum going to the distributor. The distributor should then retard that automatically if the computer is working correctly. Since the computer (or some sensors or something) isn't working correctly, it appears to always leave it at full vacuum. With the nutter bypass, it will be reconnecting using ported vacuum, but only after I bypass and disconnect the computer (which is supposed to control the electronic component of the distributor?). So, do I need a new, pre-computer distributor? Are there wires hooked to it or something? I don't remember wires going to the distributor, so how does it know what to set the timing at?

 

[Guest]

No, you don't need a new distributor. What I can't find is the original drawing that shows which wires to cut and run new wires to. I did the HEI conversion 2 years ago and I have removed all computer wiring from my harness so I can't run out and look at my CJ to tell you for sure how to wire it up. But here is a schematic of the computer wiring harness: http://home.sprynet.com/%7Edale02/wire-big.htm You will see the purple and orange wires coming out of the connector for the distributor going to the computer. You will also see purple and orange wires between the ignition module and the module's plug. If I remember this right, and I hope someone out there who has done this will correct me if I'm wrong, you cut the orange and purple wires between the ignition module and the module's plug. You will then splice in two wires to the wires you have cut coming out of the module. You will run those two wires over to the plug going into the distributor. You will then cut the orange and purple wire at the distributor plug. Splice the two wires into the wires going into the distributor plug. Keeping them straight, splice orange to orange and purple to purple. The engine should now fire up when you start it. If it does, the computer is now out of the loop. Now, retime the engine at about 8 degrees BTDC at about 700 RPM. Finally, hook a vacuum line up from the ported line coming off of the carb and run it to the distributor. Of course the metering pins on the carb need to be set, but if your computer is dead like mine was, you will have to set them manually. I was fortunate the pins were in the right position when I did this. Hope this helps.