how to test oil filled ignition coil

by:Haiyan     2023-06-23

How to Test Oil Filled Ignition Coil


The ignition coil is a critical part of the ignition system in modern combustion engines. It generates high voltage pulses to initiate the spark required for fuel combustion. Oil filled ignition coils are commonly used in many vehicles due to their durability and effectiveness. However, like any other automotive component, they can experience wear and tear over time. In this article, we will learn how to effectively test oil filled ignition coils to ensure they are in good working condition.

1. Understanding the Basics of an Oil Filled Ignition Coil:

Before we jump into testing, let's first understand the basic structure of an oil filled ignition coil. These coils contain a primary and secondary winding, separated by an iron core. The primary winding receives low voltage current from the vehicle's battery, while the secondary winding produces high voltage pulses which are then distributed to the spark plugs. The oil within the coil helps with heat dissipation and ensures more efficient operation.

2. Checking for Physical Damage:

The first step in testing an oil filled ignition coil is to inspect it for any physical damage. Look for cracks, corrosion, or oil leakage around the coil. Any such damage could indicate a fault in the coil and should be addressed before further testing. Additionally, verify that all connections and wires are secure and properly connected.

3. Testing Primary Winding Resistance:

To test the primary winding resistance, you will require a digital multimeter. Set the meter to resistance mode and measure the resistance across the positive and negative terminals of the coil. Consult the manufacturer's specifications to determine the acceptable resistance range. Any reading significantly higher or lower than the specified range could indicate a problem with the primary winding.

4. Testing Secondary Winding Resistance:

Similar to the primary winding, the secondary winding should also be tested for resistance. Using the multimeter, connect one probe to the positive terminal of the coil and the other probe to the high voltage output terminal. Again, refer to the manufacturer's specifications for the acceptable resistance range. If the reading falls outside the specified range, it may indicate a problem with the secondary winding.

5. Performing a Spark Test:

A spark test is a useful way to determine if the ignition coil is generating sufficient voltage. Start by disconnecting one spark plug wire from the spark plug. Insert a spark plug tester into the spark plug wire boot and ground the tester to a metal surface on the vehicle. Have someone start the engine while you observe the spark tester. A healthy coil will produce a bright blue spark. If the spark is weak or absent, it may indicate a faulty ignition coil.

6. Testing the Coil Under Load:

To assess the coil's performance under load, you can use a tool called a spark checker or an adjustable spark tester. These tools simulate the load that the coil experiences during normal engine operation. Connect the tool to the coil's high voltage terminal and ground it to the engine. With the engine running, check for a strong, consistent spark. If the spark is weak or intermittent, it could indicate an issue with the coil.


Regularly testing your oil filled ignition coil is essential for maintaining the overall efficiency of your vehicle's ignition system. By following the steps outlined in this article, you can ensure that your coil is operating optimally. If any problems are detected during the testing process, it is recommended to consult an automotive professional for further inspection and potential replacement. Remember, a properly functioning ignition coil is crucial for reliable engine performance and fuel efficiency.

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