Coil packs are a critical component of your car’s ignition system, responsible for providing the spark needed to ignite the fuel-air mixture in your engine. A faulty coil pack can lead to a variety of performance issues, from engine misfires and reduced fuel efficiency to a complete inability to start your vehicle. Testing your coil packs is a straightforward diagnostic procedure that can save you time and money by identifying whether a coil pack is the source of your engine problems.
This guide provides a step-by-step process for testing coil packs using a multimeter. While the vehicle in the images is a 1993 BMW 325i, the general principles and testing methods apply to most modern vehicles.
First, locate the coil packs in your engine bay. Typically, they are positioned on top of or near the engine, directly connected to the spark plugs. In many vehicles, a plastic engine cover will need to be removed to access them.
To begin, ensure the engine is off and cool to prevent burns. Carefully remove the engine cover, if present, to expose the coil packs.
Once the coil packs are accessible, disconnect the electrical connector from each coil pack. Most connectors have a small metal or plastic clip that needs to be lifted or pressed to release the connector. Gently pull the connector straight out from the coil pack.
Next, you will need to unbolt each coil pack from the engine. Typically, coil packs are secured by two 10mm bolts each. There may also be ground wires attached to these bolts, connecting all the coil packs and a ground strap to the engine head. Remove these bolts and set them aside. Once unbolted, the coil packs should lift straight out. You might need to apply a slight twisting or pulling motion, but they should come out without excessive force.
With the coil packs removed, you can now proceed to test them. For this, you will need a digital multimeter (DMM). A basic and inexpensive multimeter is sufficient for this task.
Set your multimeter to the lowest Ohms setting (resistance measurement). This is usually indicated by the Omega symbol (Ω). The Bentley Manual for BMW I-6 engines specifies a resistance range of 0.4 – 0.8 ohms across the two end terminals of the coil pack. Consult your vehicle’s repair manual for the specific resistance range for your coil packs.
To test the coil pack, touch one multimeter lead (either positive or negative) to one of the end terminals of the coil pack, and the other lead to the opposite end terminal. Observe the resistance reading on the multimeter display. Repeat this process for each coil pack.
Compare the resistance readings you obtained for each coil pack with the specification in your vehicle’s repair manual. Readings outside the specified range indicate a faulty coil pack that should be replaced. In this example, all coil packs read 0.8 ohms, which is within the acceptable range, suggesting they are functioning correctly.
Before reinstalling the coil packs, it’s good practice to clean the spark plug wells. Use a vacuum cleaner to remove any debris that may have accumulated around the spark plugs. This prevents dirt from falling into the combustion chamber when the spark plugs are removed or replaced.
For hard-to-reach areas, a vacuum extension or a narrow nozzle attachment can be very helpful in thoroughly cleaning around the spark plug holes.
Finally, if you are replacing spark plugs, install the new spark plugs. Ensure they are the correct type for your vehicle (refer to your owner’s manual or parts catalog). In this case, NGK BKR6EK spark plugs are being installed, which are the correct plugs for this BMW model.
Reinstall the coil packs in reverse order of removal, ensuring they are securely bolted and the electrical connectors are firmly attached.
Testing coil packs is a simple yet effective way to diagnose ignition system problems. By following these steps, you can confidently test your coil packs and determine if they are contributing to engine performance issues. If your coil packs fail the resistance test, replacing them can restore engine performance and efficiency.
