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post #4 of (permalink) Old 06-13-2019, 07:24 AM
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Join Date: Dec 2009
Location: Central PA
Posts: 277
Another explanation on how to check ignition coil operation. The coil (like an OE coil on the Alfa Spider) has two side posts and a center post. The side posts are for the Primary ignition and the center is for the Secondary ignition. The Primary works this way: With the key on and the ignition energized, 12v+ is sent to the + terminal on the coil (sometimes has a 15 designation). When the engine is cranked (and running) the other side, the - terminal (sometimes has a 1 designation), receives a pulsed 12v+ signal from the contact breaker points or the ECU. This is the pulse or trigger that enables the magic to happen inside the coil that produces the energy that comes out of the center post of the coil that goes through the "coil wire" into the dizzy cap that then comes out of the dizzy cap and goes to each spark plug. To test: I use a "test light". Looks like a screw driver with a light bulb in the handle. Always check the operation of the test light on a known good battery first. Before testing, make sure that all the wires are connected to the coil and are in good condition. With the ignition on, test the + side terminal for 12v+. If good, then crank the engine to test the other side terminal, the - terminal, to see if it is getting a pulse (blinking light on the test light bulb). If good, test for a good spark energy coming out of the center coil wire. You can hold it next to a ground connection (with insulated pliers) or use a dummy spark plug. If good, then it is time to look inside the dizzy. Bad rotor or bad cap, or bad spark plug wires or bad spark plugs. If you don't have a good result at coil+ or coil-, you have either a wiring, or sensor, or ecu problem. Good luck!

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