"Nutter Bypass" Do I need to do it?

**Donobrew** · 05-14-2009, 12:45 PM

Do I need or should I do a nutter bypass if my CJ7 runs good? Everything is stock except the TFI upgrade. Does the bypass improve mileage or power?

**Mike Romain** · 05-14-2009, 01:12 PM

What exactly is a TFI upgrade?

**texasdave** · 05-14-2009, 01:29 PM

Did you mean a TBI upgrade? If so you need a computer for a TBI which would indicate the original computer was replaced in the process.

**Mike Romain** · 05-14-2009, 02:58 PM

OK I looked it up, the teamrush upgrade basically, a new cap rotor and coil.

If it is running good then...

Taking the emissions computer out is usually on older systems with troubles already, but it basically gives another seat of the pants 25% boost in power. The engine will rev up to 4400 after, well mine will.

If you need emissions testing, then you may not want to do this or you can just do the wiring part with spade connectors so it can be reversed easy if needed and leave all the rest of the shut off stuff in place for later.

chill254 · 05-15-2009, 09:09 AM

Doing the nutter bypass will improve the way the vechile runs. Imagine all of the sensors that are going on 25 years old. Some of them are definatly past ther prime. IMOP I would do it (I am in the process right now of rebuilding my jeep and the computer, all of the wires, and all of the sensors are gone). If you have to pass emissions I would follow Mike Romain's advice.

****Make sure that you understand that you will loose whatever spark advance the computer gave (about 7 deg). The distributor's mechanical advance will only give 6.75 or 7.75 deg of advance once the computer is removed. You must replace the newer limiter in the distributor with a older one (before the timing computer 80 and bellow I think). Then you will have the original full advance of either the stock 13 deg or by fliping the limiter 18 deg. You don't hear people talk about this much with the nutter but it is important. I don't know of a place that sells just the limiter so you might have to dig around for one.***

**foggybottombob** · 05-15-2009, 09:27 AM

If your computer is not controlling your carb (as was the case for me) then the Nutter bypass is something to do for sure. The stepper motor on the back of my Carter BBD never moved while I had it all connected so it was broken when I bought it.

**Mike Romain** · 05-15-2009, 09:36 AM

Quote:

Originally Posted by chill254

****Make sure that you understand that you will loose whatever spark advance the computer gave (about 7 deg). The distributor's mechanical advance will only give 6.75 or 7.75 deg of advance once the computer is removed. You must replace the newer limiter in the distributor with a older one (before the timing computer 80 and bellow I think). Then you will have the original full advance of either the stock 13 deg or by fliping the limiter 18 deg. You don't hear people talk about this much with the nutter but it is important. I don't know of a place that sells just the limiter so you might have to dig around for one.***

I haven't had an issue with the advance. It actually advances far and fast enough with a base setting of 9 BTDC at idle to need high octane gas to avoid pings. The knock sensor was in there to dump the timing back and was needed, it is dead after the Nutter.

Same for gas mileage, 91 octane gives me about 5 mpg better than 87 and way more punch over 60 mph with the Nutter, not so with the computer.

I have seen the posts for playing with the advance and have only read of headache after headache when folks try to get too much in there, never a real success story on a 'stock' engine that I remember. Now if you have a cam and a big carb and headers, well....

chill254 · 05-15-2009, 09:56 AM

What I am saying is that every distributor that came with a computer has a different limiter that those that came without a computer. If your goal by doing the nutter bypass is to remove the computer so that it will run like those that came without a computer then you also need to change the limiter. The purpose of the mechanical advance is to advance the timing with respect to the engine rpm. The FACTORY setup before the introduction of the computer was 13 DEG max of mechanical advance. The FACTORY setup with the computer was 7.75 DEG max. The extra timing comes from the computer. Your inital timing is the 9 DEG BTDC then there is the machanical advance (RPM based) then there is the vacuume advance (load based). Basicly The FACTORY setup for a 258 without the computer is 13 DEG max mechanical advance with one light ond one heavy spring. No playing around here this would have been the way they came if they did not have the computer.;

**Mike Romain** · 05-15-2009, 10:08 AM

Quote:

Originally Posted by chill254

What I am saying is that every distributor that came with a computer has a different limiter that those that came without a computer.

I didn't know about this before this group found me and was freely mixing and matching parts in mine from the 78 to the 86 distributor when testing out other engines and never noticed any difference. I am not even sure 'which' one I have in right now, but think it may be the 78 one. I guess the next time I have the timing light out I can find out.

I can't see how any more advance could benefit though when it pings now at 9 base without 91 octane. I likely have the 78 I guess, but the 86 also pinged the same, I drove it for a few years Nuttered before the engine swap...

chill254 · 05-15-2009, 10:14 AM

I didn't know until I read something jeephammer put up. So I took mine apart and sure enough only 6.75 or 7.75 deg of max mechanical advance. I bought a used distributer and am in the process of replacing the computer limiter. I don't advise playing with the timing beyond changeing out the springs and then only small changes at a time. There are too many horror stories about guys who killed there engine. The timing of when the spark fires is a sensitive thing. You will have to take the distributor apart to find out which limiter you have. Well I guess you could plug the vacuume advance and rev the engine to about 3000 and check the total timing. The mechanical should be all the way in and if you subtract out your inital timing that should leave you with the total mechanical advance. There is an article on here somewhere that jeephammer has some good stuff. If I find it I will post it up.

Sorry donobrew not trying to jack your thread.

**Mike Romain** · 05-15-2009, 10:24 AM

Quote:

Originally Posted by chill254

I didn't know until I read something jeephammer put up. .

I read the same post. I believe my mechanical is all in before 2000 rpm if I remember my last test and it was a fair bit up above the scale.

**Donobrew** · 05-15-2009, 10:38 AM

Thanks for the info... One question, After the bypass I'll need to advance the timing to 8 or 9* BTDC, right?

**Mike Romain** · 05-15-2009, 10:49 AM

Quote:

Originally Posted by donobrew

Thanks for the info... One question, After the bypass I'll need to advance the timing to 8 or 9* BTDC, right?

Correct. This gets set at idle with the vacuum line off and blocked.

You also have to manually set the idle mix screws and set the stepper motor air bypass pins up in the center of their travel.

Are your idle mix screws down front broken open or still factory sealed?

chill254 · 05-15-2009, 10:53 AM

Also with the computer removed you can set your timing at the curb idle of 680. There is no need to rev up the engine to set the timing once the computer is removed.

**Donobrew** · 05-18-2009, 03:36 PM

OK, I sent the stepper motor pins and disconnected it. I bypassed the computer (purple and orange wires) and reconnected them to the ignition module.
Connected the vacuum line going to the distributor to the ported vacuum line. Now for the timing, took the vacuum line off the dist and block it, I start it up and hit it with the light and I was already at 8* BTDC. Question, should it have been??
The jeep seems to ride fine. Took it on the highway and it motored 65-70mph no problem like before… It does seem to start better and not need to warm up very long…