Can somebody explain the purpose of the computer, under dash, in the 80' thru 86' trucks? I know in the 87' thru 96' trucks it controls the fuel injection and ignition system, but since my 84 engine has a carb and the ignition box on the fender, why does it need a comp?
Pardon me if this is dumb question.
Thanks for any input!

 

Not all 1980-1986 trucks have computers.


Some have nothing but a Duraspark ignition module.

Some have the MCU (Microcomputer Control Unit) like mine does that is bolted above the Duraspark II ignition module on the left fender apron.

Some have an EEC-III, which was only used in California I believe.

And some like you are describing have the EEC-IV. On the EEC IV system used for feedback Carbs, it basicly does a simular type of engine control as it does on a Fuel injected model.

The Carburetor has a Feedback solenoid, that changes the fuel mixture. And there is an o2 sensor in the exaust system. In optimum conditions, The computer reads the o2 sensor, and adjust the fuel mixture at the feedback solenoid on the carb, to an optimum level saving you gasoline, and reducing emissions. The computer also has a limp home mose where it sends a preset mixture ratio to the feedback solenoid under certain conditions without relying on the o2 sensor, although it's not as acurate, and burns more fuel and causes more pollutants etc...

The EEC-IV computer also controls EGR valve operation on some models, Throttle position, Thermactor system (Cat converter and air pump, is a part of the thermactor system etc.) and it also controls and gets feedback from the TFI-IV ignition module as it does on the fuel injected models.

 

Thank you very much. This is exactly the info I wanted.
So basicly, I won't need the computer since my engine has absolutley emission stuff and no o2 sensor? The air pump and its plumbing is gone also.

 

If your distributor doesn't have a vacuum line connection, then you do need the computer, or you need to change the distributor. With no computer and or half the sensors gone on the engine, you will have no timing control and no timing advance, since the computer controlled distributor has no weights or vaccum advance on it. Your timing will be locked at one position giving you less power and crappy fuel mileage.

 

The distributor is vaccum advanced.
That means I should be in the clear?

 

Yes, someone must have converted everything over. I assume you have a different carb too(no wires going to the carb except possibly the choke).

 

Ok, great. Theres not even an electirc choke. My cousin used to drive the donor truck and I put a manual choke in it for him.
Another question, A guy I've been getting advice for the swap told me that all I have to do is find a wire that becomes energized when I turn the key on, and wire the Igtniton Module to it. Sound Legit?

 

You need two of those wires. On that is hot directly from the key and goes to the module, and another that is hot from the key, goes through a resistor, and then to the coil +. Here's a diagram. I am assuming you are using the Ford duraspark II system.

 

ahhh. Very helpful. So pretty much, the red wire comes from the switch directly, and the white is a ground? While another wire comes form the switch, through a resistor and then directly to the coil? duraspark II is what im using.

 

I have never seen a white ground wire, what is making you see that?

 

Well after looking closely, assuming the white was a ground was kinda dumb of me. When they say starter relay do they mean strarter soleniod?

 

Yes, that is the starter solenoid. The white wire is a spark retard wire. When there is 12 volts on the white wire, the module retards the timing a set amount, and it makes the engine turn over easier. It's good for the battery and the starter. So you just run a wire from the "s" terminal to the white wire of the module.

 

there goes franklin with his infinite resources..... its like he has a data base somwhere with all the knowlege of the universe or something.... sereously how do you find this stuff?? if i needed a engine block for a 1894 mercedes he could find me one in the backyard of a vietcong prison complete with rebuilding instructions in 7 languages including latin. thats crazy man!

 

haha! Sounds like your have youself a very knowledgable person over here.
One more question, this resistor in which you speak of. Do I get that from the donor truck or a parts store? If I get it from the donor truck, what does it look like?

 

You can get the replacement resistor at a parts store.

The original will have two black round rubber blocks, to help identify the splices between the regular wire, and the resistor, and the resistor wire itself will be marked, "Resistor Wire - Do not Cut or Splice."