The coil pack in a car is responsible for delivering a clean strong spark to the spark plugs. A defective coil pack can cause an intermittent spark, as well as a weak spark. Heat can create problems for a coil pack causing internal damage. You can check the coil with only a few tools and a basic knowledge of cars.
Park the vehicle on level ground and set the emergency brake. Open the bonnet of the vehicle.
Disconnect the spark plug wires from the spark plugs. Label the wires for proper replacement. Follow back the spark plug wires to the coil pack.
Disconnect the coil pack by pulling on the electrical connector in the centre of the pack.
Remove the coil pack using the wrench to unbolt the support bracket. Place the coil on a work bench, with the terminal facing up.
Turn on the volt meter and turn the dial to 20,000 ohms. Place the volt meter black lead to the centre of the coil pack where the spark plug wire is connected. Place the red meter lead to the positive terminal on the coil. This checks the secondary resistance. Check the readings against your car's service manual to determine the proper operating range.
Set the volt meter to 10 ohms, and touch the terminal "B+" found on top of the coil. Use the red meter lead. Touch the negative terminal with the black meter lead. This will test the primary resistance. Check the readings against the vehicles service manual for proper range of operation.