Mechanics

IGNITION COIL IS FUALTY

1995 Jeep YJ

Engine Mechanical problem
1995 Jeep YJ 6 cyl Four Wheel Drive Automatic 68,000 miles

I was driving on the highway when I had complete power loss to my vehicle and this is not the first time that it has happened. The problem is usually a faulty ignition coil. Recently after taking it in to a mechanic we found that it was the magnetic pick up that was losing its magnetism and causing the coil to go bad about 6 months ago. Now, again this time I tested the coil myself and the primary coil resistance was around 1.5ohms? The secondary coil might be the part that is faulty although I’m not getting a reading with my multimeter. My question is how I might test the magnetic pick up myself to see if that is the source of the problem or if there is even something beyond that could be the problem. I know when the mechanic showed me he hooked it up to a circuit light meter to see if it glowed correct me if I’m wrong? Also my question as well is how I should approach this if the coil is faulty due to this source of power loss.
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Tjburns44
July 20, 2010.



Hi tjburns44. Welcome to the forum. I had to scratch my head a few times. It's possible your mechanic doesn't understand how these circuits work, but I think it's more likely he just isn't good at explaining it. An ignition coil becomes defective on its own. Nothing else will cause it to fail. And magnetic sensors don't lose their magnetism. If you look at your crankshaft position sensor, I believe you will find it has three wires. (I'm doing this from foggy memory). Three wires means there is circuitry inside the sensor that amplifies the pulses generated by a coil of wire wrapped around the magnet. Those types of sensors fail often and can become heat-sensitive. Another version of this is the Hall Effect Switch which replaces the coil of wire with a magnetically-controlled transistor.

Two-wire sensors are also a magnet with wire wrapped around them but they produce a high enough signal that no other circuitry is needed. They connect directly to the ignition module or Engine Computer.

While I suppose it is possible for the magnet in a sensor to lose its magnetism, I suspect what your mechanic meant was it was losing its signal. That WILL cause the engine to stall suddenly. Magnetism won't be lost that fast to cause abrupt stalling.

I had to use '97 service information, but I think the circuitry is the same. You should have a crankshaft position sensor and a camshaft position sensor. Both have three wires, a 5.0 volt power supply for the internal circuitry, a ground wire, and the signal wire. If these sensors are working, the Engine Computer will turn on the automatic shutdown relay anytime the engine is rotating, (cranking or running). When the ASD relay turns on, it sends voltage to the ignition coil, injectors, fuel pump or pump relay, oxygen sensor heaters, and alternator field. The most obvious clue is the fuel pump but it can be hard to hear. Instead, use a test light or cheap digital voltmeter to measure for that voltage on the green wire with black stripe at the ignition coil. If you find battery voltage there during cranking, the sensors are working.

Caradiodoc

Caradiodoc
Jul 21, 2010.