How to Detect and Replace a Faulty Ignition Coil

February 27, 2012

Learn the signs of an ignition coil needing replacement, how to test it, and how to actually replace an ignition coil.

Ignition Coil

A faulty ignition coil can result in several frustrating issues with your car's engine. Fortunately, a faulty ignition coil is one of the least expensive car repairs. You should be able to diagnose a faulty ignition coil before having to replace it.

Symptoms of a Faulty Ignition Coil
One of the most common symptoms of a faulty ignition coil is when the vehicle runs for a while and then the car's engine suddenly dies for no apparent reason. This occurs after the ignition coil or module gets too hot, and usually will correct itself after the engine module cools. In some cases, a bad ignition coil will result in the vehicle not starting it all. Or, it may have characteristics of a flooded carburetor, where the vehicle runs very poorly or jerks and stops erratically.

How to Test for a Faulty Coil
A quick way to test for a faulty coil is to allow the vehicle for run for about 30 minutes and then gently rap the module with the head of a screwdriver. If the car engine dies, this is a good indicator that the ignition coil is faulty and needs to be replaced.

You can also use a test light or standard voltmeter (multi-meter) to check the resistance on the ignition coil. As with all types of ignition system repairs for your vehicle, you should make sure to purchase a manual for your vehicle from the local auto parts store searches those published by Chilton or Haynes.

How to Replace a Faulty Ignition Coil

This repair is relatively simple. While the replacement of an ignition coil will vary from vehicle to vehicle, here are some general guidelines to help you perform a replacement.

What You Will Need

  • Wrenches
  • Screwdrivers
  • A new ignition coil
  • A torque wrench
  • Dielectric compound
  • A Chilton or Haynes car repair manual (optional, but recommended)

Disconnect the Battery
Before getting started, remove the ground or negative terminal cable from your car's battery. Because you will be working with your vehicle's electrical system, this will help you avoid serious injury or shock when removing the old ignition coil or installing the new one.

Remove the Ignition Coil
Use a small screwdriver or wrench to remove the screws or fasteners that attach the ignition coil to the electrical connector. Then, twist the ignition coil slightly so that you can remove it. Depending on the type of engine your vehicle has, you will have to rotate the ignition coil so it can clear the fuel injectors or fuel injector rails.

Apply Dielectric Compound
Apply a thin layer of dielectric compound on the rubber boots or bottom portion of the new replacement ignition coil.

Install the New Ignition Coil
Next, insert the new ignition coil. In most cases, you'll want to use a stock replacement ignition coil because it's already been adjusted for use with your car's engine. However, there are universal ignition coils that you can purchase for the vehicle as well.

Apply the Appropriate Torque
Refer to the Chilton's or Haynes manual for the correct amount of torque to be applied to the coil bolts on the new ignition coil. Then, using a torque wrench, apply the appropriate amount of torque to properly secure the coil bolts.

Reconnect the Battery
After you have installed the new ignition coil, reconnect the negative terminal cable to the car battery.

Start the Engine
Start the engine and insure all cylinders are firing properly.

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