Initial or repeat failure of an ignition coil could be caused by high resistance or missing chassis or body grounds. The bad grounds to the ignition coil can reduce the amount of current flowing through a coil. The coil will then have to work harder to transform low-voltage/high current energy in the primary coil into high-voltage/low-current energy in the secondary windings. This video is sponsored by Blue Streak.
Grounds on the primary side of the ignition coils typically use a single point on the chassis or body. The location and routing of the ground distribution can be found in the wiring diagram.
The post or connectors can become corroded or damaged where the harness connects to the body. On some vehicles, the harness can be damaged by heat, leaking oil or physical damage.
To confirm the condition of the ground on the circuit, you CAN use a meter to test for resistance or open circuits. But, a meter will only give a limited view into the health of the circuit.
Using a low-amperage current probe to measure the current “ramp” through the primary ignition circuit is perhaps the most definitive method of determining the electrical integrity of the coil and the quality of the grounds and primary windings. Many defective ignition coils, for example, will pass a resistance test but fail a current ramp test. When testing multiple coil systems, the current ramp gives an excellent comparison of current flow through each coil in the ignition system and usually helps the technician arrive at a more accurate diagnostic conclusion.
Looking at a normal waveform, there is a smooth ramp as the primary is saturated with energy. The ramp will top out and drop quickly. If the ground for the coil or circuit is damaged, the waveform will be flat or shallow compared to the other coils.
In addition, don’t forget the condition of the spark plugs themselves as a contributing factor. When replacing an ignition coil that has failed, replacing the spark plugs and the other ignition coils is always recommended to prevent comebacks.