Common Ignition Coil Problems

Common ignition coil problems is something of a misnomer. Approximately 80 percent of the time it is the mechanism that controls the coil that fails. With this in mind, don't be too quick to replace your coil. Check the other controlling devices first.

Single, Stand-Alone Coils

These are the oldest style of coils. These coils are oil-filled to dissipate heat buildup in the windings. Some of these coils are designed to operate on six volts and need to have a ballast resister located in-line to drop the voltage. If the ballast resister fails, the coil fails due to lack of power. If the ballast resister is not installed, the coil heats up and fails. The only other problems that are common are cracks in the coil tower, which causes arcing to the negative terminal and loss of oil due to a case leak.

The early models are controlled by a set of points within the distributor. If the dwell is not set properly or if the points are burnt, the coil output would be dramatically reduced, resulting in a rough running engine with no power. If the points fail, the coil ceases to operate.

In the -70s, General Motors redesigned the coil to fit in the top of the distributor cap. It eliminated the points in favor of a hall-effect sensor and an ignition module in the location where the points are located. The hall-effect sensor is a stationary magnet, and blades are used on the distributor shaft: one for each cylinder. As the blades rotate where they are close in line with the sensor, voltage is high, and as they pass the sensor, voltage is low. The ignition module senses the voltage spikes and activates the coil using this signal. Most of the time, the ignition module is the culprit when there is a coil failure. This is the case with all systems using an ignition control module. This system is the HEI (high energy ignition) system for high energy ignition. It is capable of 50,000 volts.

HEI modules should be tested for voltage to the module and pulses coming out to the coil.  A common problem encountered is with the coil terminal inside the distributor. This secondary terminal is inserted through the center of the distributor through the top. The coil sits on the terminal and transmits it power through this terminal. The terminal wears down and causes a serious misfire.

Later model vehicles with fuel injection have a series of sensors, a computer and an ignition model. A crankshaft sensor is used to determine the location of top dead center of the number 1 cylinder. This signal is transmitted to the ignition control module, which transmits the signal to the computer. The computer analyzes the signal and returns a signal to the control module as to the time to fire the coil. A failure in any of these will cause the coil to be inoperative.

Many foreign cars use an igniter located outside the distributor, which acts the same as the ignition control module.

Another version of the ignition system is the wasted spark system. Many domestic vehicles use this. There is one coil pack, as it is called, for two cylinders. Each coil has two coil towers and fire two spark plug wires simultaneously. It is always perched on top of an ignition control module. These units have problems with the control module about 60 percent of the time. The rest of the time, the problem is with the coils. The reason for this is that they are susceptible to overheating. The bottom control module was packed and sealed in a gel that melts and causes failure.

The latest development is the coil on plug system. This system has one coil for every spark plug. These units use a stand-alone ignition module or the computer, or a combination of both for control of the coils. The good thing with this system is that a coil failure only effects one cylinder, causing a singular misfire. The bad thing is that they fail more often then the older ignition coil-module setups. There is a spark plug boot attached to the bottom of the coil, which reaches to the plug. These boots break and cause a short to the valve cover.

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