1984 2.5 lt XJ, what the computer does?

Folks,

My 1984 2.5 lt XJ came with a carb (obviously). Now, I've replaced that with a Weber, and I did the Nutter conversion, where the ignition is no longer controlled by the computer.

The question is, what else is that computer doing (if anything!)? And where on earth is it located?

Thanks for your time.
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John SV1CEC

It's that little box on the pass. side fenderwell that says AMC on it.

Can't help ya with what else it does. you can disconnect the wiring to it and then see if the Jeep still works.

The Carter YFA carb has a computer controlled jet and controls the mixture based on MAP/air charge sensors. The computer also controls the timing.

CheapXJ said:

It's that little box on the pass. side fenderwell that says AMC on it.

Can't help ya with what else it does. you can disconnect the wiring to it and then see if the Jeep still works.

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Ummm no. The computer on my 84 was under the dash drivers side near the steering wheel but to the right. But yes it controls the timing. It also controls the CEC Fuel Feedback System. Um Old Man I hate to correct youi but the 84 did not havev a MAP sensor. :wierd:

After seeing a reference to the "Nutter bypass" on SV1CEC's web site I looked it up. Not 100% certain, but I think his ECU is now nothing but ballast. It isn't controlling the carb, because he doesn't have a computer-controlled carb any more, and I think the Nutter bypass essentially returns timing to approximately what a pre-computer distributor would have been ... timing controlled by vacuum and centifugal weights.

Sorry about the MAP issue. It's been so long and my rig has been through so many incarnations. It started out as a carb'd 2.5L bone stock w ax-4, not even power steering. I rebuilt it converted it to tbi, added a cam and headers and an ax-5 Then I swapped in a 4.7L stroker w/ax-15. Last week I swapped out the ax-15 for an AW-4. Other than the base core unibody, absolutely the only thing that is original is the steering wheel.

old_man said:

Sorry about the MAP issue. It's been so long and my rig has been through so many incarnations. It started out as a carb'd 2.5L bone stock w ax-4, not even power steering. I rebuilt it converted it to tbi, added a cam and headers and an ax-5 Then I swapped in a 4.7L stroker w/ax-15. Last week I swapped out the ax-15 for an AW-4. Other than the base core unibody, absolutely the only thing that is original is the steering wheel.

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I know the feeling! Just wanted to make sure our friend on the other side was not looking fo rsomething that was not there! LOL! It's all good! And Eagle I did not even look at that part (Nutter bypass) but if the carb is out of the pictures then from what I can tell about the MCU as the FSM calls it it is just ballast. The MCU is there for fuel economy and takes inputs from 13 different sensors for lack of a better term. One of them is the Mixture Control Solenoid that is on the YFA carberator. I'll have to check into this "Nutter Bypass!" Sounds like the bypas that was done on mine.

Edit/ Yep that would be the bypass the computer mod that is part of the Webber conversion. By the way who is the babe in the beach shot? :yelclap: :wow: Pre or post twinns? /Edit

OK guys, so that, essentially means that I can discard it, right? Not that it bothers me at all, but since it's not doing anything, why should it be there?

Anyone has any FSM diagrams about this box? It would be interesting to trace the wires.

Ghost, the babe is my wife, I've just bookmarked this thread, so that I can show it to her when she gets back from Ukraine, I am sure she will love the compliment. Oh, and the picture was taken six months after the twins birth. Thank you!!!

Rgds to all who spend time answering.
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John SV1CEC

SV1CEC said:

Anyone has any FSM diagrams about this box? It would be interesting to trace the wires.

Ghost, the babe is my wife, I've just bookmarked this thread, so that I can show it to her when she gets back from Ukraine, I am sure she will love the compliment. Oh, and the picture was taken six months after the twins birth. Thank you!!!

Rgds to all who spend time answering.
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John SV1CEC

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:shocked: Boy she sure did well! Hope that does not offend! But WOW! :cheers: Ihave a FSM from 85-87. It is what I call a bastard FSM. Email me: [email protected] and let me know what you want and I'll see if I can scan and email the pages to you. Incedently i scored an 84 sales brochier on ebay last month. It is really intresting.

John, my '85 is set up exactly the same way...the only thing I miss is the ability for the system to regulate the idle speed according to load...Eg: when the a/c is running... The "Nutter bypass" is essentially reworking the ignition to stand-alone operation by splicing in a Ford "blue grommet" ignition module.
Costs 17 bucks at AutoZone.

MudDawg said:

John, my '85 is set up exactly the same way...the only thing I miss is the ability for the system to regulate the idle speed according to load...Eg: when the a/c is running... The "Nutter bypass" is essentially reworking the ignition to stand-alone operation by splicing in a Ford "blue grommet" ignition module.
Costs 17 bucks at AutoZone.

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Yeah, you are right, the same thing bothers me too. I was thinking to do a handle-throttle mod, using a bicycle gears mechanism, that could act as a high-idle lever for those difficult instances. However, I never got the chance to do it until now (what with the twins etc.). Maybe now that the babies are gone, I'll find the time to do it, I just need to set my priorities right.

I spend most weekends of this month, changing the whole dashboard (I found an abandoned Commanche, and I grabbed whatever I could from it).

Re. that Ford thing, could you please be more specific? One thing that worries me, is that if something goes wrong with that stupid electronic ignition module I have in the truck, I'll be totally stuck, I sincerely doubt if the local DC has such a spare part, and I am interested in finding an alternative. In my old rallying days, we had two full sets of ignition (2 electronic boxes and 2 coils) mounted side by side, just in case one failed. We just swapped the wires to the second set and kept going. Maybe I should do something similar on my old XJ.

One more thing. If you have a Weber in your truck, do you have a flat spot below 3000 RPMs, if you floor the throttle? In mine, it hick-up when I floor it at that region, and then it picks up. I am not sure what I can do about it.

Rgds
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John SV1CEC

I have two boxes and two coils in my spare parts bin left over after the swap. The boxes are cheap here $20 and the coils are nto too bad at $40!