Ignition Coil Testing “Waste spark ignition system”:

Ignition Coil Testing “Waste spark ignition system”:

All late model Subaru four cylinder engines employ a “waste spark” ignition coil system. Each time the ignition coil fires, it provides a spark to two cylinders at exactly the same time. Since only one of the two cylinders is on the compression stroke when the coil fires, the spark to the second cylinder (which is on the exhaust stroke) is “wasted. ”

Ignition Coil Testing "Waste spark ignition sytem": A subaru waste spark coil pack.
Ignition Coil Testing “Waste spark ignition sytem”: A subaru waste spark coil pack.

The ignition coil sits on top of the intake manifold and is divided into two halves. One half provides the spark to the number 1 and 2 cylinders, and the other half provides the spark to the number 3 and 4 cylinders. Instead of the familiar single secondary coil terminal, this coil has four secondary coil terminals.

Testing methods for this type of coil are slightly different from what you might be accustomed to as well. Using an accurate DMM, inspect the following items, and replace the ignition coil if it is found to be defective:

• Primary resistance

• Secondary resistance

Caution: If the resistance is extremely low, this indicates the presence of a short circuit.

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