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ignition pulse wire for 85-87 mpfi


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i have conflicting info on my wiring diagrams.

my diagram shows a wire from the negative of the coil going to the computer. its supposed to be straight yellow. my engine harness has no yellow wire, just striped ones. also the diagram says it will change to a shielded wire:-\

 

i need to know what color this wire should be. close to the computer. maybe this is too vague, i just gotta figure where to hookup my ignition pulse. i wuld hate to give power to my ground side of the coil.

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what yearis your schematic for?

the 87 uses the crank angle optical disty, wheras 85-86 uses a mechanical tyoe with stand-alone knock control unit.

 

the shielded wire has a gray sheath, i think the middle wire id red?

 

what does the distributor look like?

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its an 85 xt motor and harness. the disty has two vac ports. i have a diagram from the net that is for the flapper style. the diagram shows a knock sensor, but i am na, so i dont have one.

i have got power to all the stuff that needs 12 volts, so i think ALL i need now is the correct igniton pulse wire, and its loud time. i only have part of the harness, so i am runing the wires that i dont have.

 

thanks

 

i was thinking it had to be that grey one

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well, the gray wire, has two wires going into it. im guessing the black one is the shield, and has to be grounded? does this sound right? also, miles, you ever smoke a computer because it was hooked up slightly wrong? because thats my biggest fear here, and why i am trying to get this figured.

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the ecu will have its black wire for ground

 

the braided portion i think would ground to the distributor or something, but its not the computers ground. its the middle sheathed wire that will be the signal wire.

 

the ecu i have exp. with was only gutted out. i havent hooked it up, because we couldnt get the flexplate bolts out to swap the motor to a flywheel.

 

i have fried mt nintendo by jumping the contacts on the cartridge to get the screen to do crazy tricks

 

i thought i have fried mt computer swapping drives when it os on, but it was an internal breaker in the power module, and everything checked out.

 

i have a spare ecu for 87 turbo if there is a way to get it to you should you fry yours. keep me up on your progress......

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Do believe that the shielded wires in the ECU wire loom, are all ready grounded at one of the grounding wires of the harness. You can check that easily enough with a multi-meter or test light.

As Miles said, the shield is a braid like that of co-axial cable, and is usually just under the outer jacket of the wire/cable.

You only need one end of it grounded. If you ground both ends, you will induce noise into the wire, not eliminate it. You don't want noise in the wire, gives false signals to the ECU.

Been studying the wiring diagram I have for the '88 XT-6. It is different than what you have, as far as the coil wires go, but I don't believe that you want to ground that Black lead that you mention.

But I have been wrong before.

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well, heres what i did.

the shield went right into a connector, that i assume had a wire on the other side that went to ground. so i grounded the shield, and then i put the wire inside of that one(turned out to be black), onto the negative side of the coil. so cold my damn soldering gun isng getting hot enough. im gonna go turn it over and see if i can get any signal to the fuel injectors. i do have spark, and fuel pressure!

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