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i have a 91 lx 5.0 5 speed that i traded to, it was equipped with a four barrel and brand new hei dizzy. i started switching it back to F.I cause all the harness was there except for the fuel injectors n such, well i bought a harness for it off a lincoln and it worked except for it had a delete for the H.E.G.O harness ground, i never thought nothing of it so i just let it be, well now im finished and its not gettin fire off the coil except when i stop turning it over it will throw one spark.. ive changed distributors, tfi modules and anything i could think of. and now i am stumped. the car was running perfect before i switched it over and now nothing, could it be that ground i didnt hook up or?? :help i need help quick, it was my daily driver and i have nothing else to drive, if anyone can help me i would greatly appreciate it, thanks all
 

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Nxcoupe is good at stuff like this. Maybe he will chime in. But i dont think he will be on here until early morning
 

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The o2 sensors are tied into the ignition circuit with a fusible link between them. They are hot in RUN. I can only assume the engine wont start if the computer isnt getting a signal from them when you turn the key. Both sensors have three wires...one ground, one key power, and one signal return to the computer.

http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

http://www.veryuseful.com/mustang/tech/engine/images/mustangMainHarness.gif

Not sure if that helps, but thought id give it a try.
 

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You are getting spark because when you turn off the key, it kills power to the coil, magnetic field collapses and you get a spark. Problem is your distributor is not interupting the ground of the coil as it should. Now, why its not doing that is the question. Does it have an msd box or the like on it? Trace the green wire off the coil, it should end up at the tfi module on the distributor.
 

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Ignition is the one thing that is seperate from the computer. The computer can alter the timing event through the spout wire, yet the tfi will still function with the spout removed and no computer control. What computer did you put in it? Where did he get power from to run his ignition? Make sure the computer ground is connected and working. Make sure it has a solid cinnection to the battery and the single wire connector is making good contact.
 

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Ok. Folliw that green wire to the tfi module.
 

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My 69 Charger did that once. It wouldn't spark until I let off the key. Mine was a balast resistor or a starter relay. I believe the starter relay put power to the coil until the starter was released or smething like that. Check a wiring diagram and see what the starter circuit does. My Chilton only goes up to 88 but i'll check it also.

Jerry
 
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