On a 83 CJ with the 258 what does the computer control besides the stepper motor on the back of the carter carb? My stepper is not even connected, what is the nutter bypass going to change? Also attempt #2 at getting the MC2100 carb is going to happen soon.
It also controls the timing advance via a knock sensor and any other electric/vacuum modules like the fast idle kick up if you have an auto or AC.
Basically if the carb is unplugged, it has gone into 'limp home' mode with the timing clamped down.
When you do the 'nutter' the timing jumps about 15 degrees with the ignition module running things like it is 'supposed' to do.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT'sRusted wrote:
Thanks for the info Mike. The MC2100 is going to be one of my next projects too.
I have gone 4+ years with no stepper and it seems to run ok. But that could explain why occasionally when I first start up the Jeep it will run super rich until I turn it off, and restart. I bet the computer is messing with the advance. I will have to take care of that issue soon. Thanks Mike.
The stepper controls mixture as commanded by the MCU. If your stepper is disconnected, the MCU can't make it rich.
Are you sure it's rich, and does it happen when started hot or cold?
Always when started cold. It is very rich during that time. It seems to run fine at low RPM, but by the time I get down the street and am still in first gear it will hardly run. As long as the RPM's are below 2000ish it is ok. If I turn it off, and back on problem is fixed.. This happens more in the winter than in the summer, I was trying to blame it on a stuck carb. Anyways I will nutter it and put on a MC2100 and see if the problem goes away.
I was just saying that if the stepper is disconnected, the MCU can't affect mixture. That said, you could still have a carb problem that does affect mixture. Such as a stuck or misadjusted choke, choke pull off, etc.
There are also two doors in the air cleaner. One is thermostatically controlled, and the other closes with the engine off to contain fuel vapor. If this door doesn't open, due to sticking, blown diaphragm or lack of vacuum, it could cause a rich condition that would get worse at higher rpm.
Are we talking rich enough to cause a black cloud coming out of the exhaust?
The 2100/2150 is a much less troublesome carb, and is much simpler. It is not affected by conditions that will cause a BBD to take a shit.
You actually are talking too lean I believe. It is deceiving.
That choke is a joke. It is on a timer that goes off according to how long it has seen power with no bearing on the reality of the engine temperature.
When you shut it off, you are resetting it to give it an extra shot of choke so it will then run until warmed up.
I got 'really' tired of having to 3 foot drive up here in our Canadian winters when it was cold, so I along with most of my friends have gone to a manual choke cable. That works great! I can keep the choke 1/4 on with the rpm at 1000 or 1250 and just drive away. When it 'really' warms up it will start to bog so I then turn off the choke.
That manual choke cable also acts as a sweet hand throttle. I use it when winching to keep the alternator putting out. I can just hold the gas pedal at 1250 rpm, then I pull on the choke let off the gas then push the choke back in. The fast idle cam will then stay at 1250 until I tap the gas pedal.
But if indeed your choke is staying on too long, then all you need to do is clean the electrical contacts. They get corroded and the choke can get it's power too slow. But if it has been the same for 4 years, I would not suspect the connection, rather just the nature of the beast.
Mike
Rusted wrote:
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