How to Replace a GM Ignition Module

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The GM Ignition Module

ignition control module icm
Replacing an ignition control module can be done at home.

If you drive a GM car or truck with a V8 engine, this tutorial will show you exactly how to replace the ignition control module (also known as the ICM) that is hiding under the distributor cap. Chevy trucks, GMC trucks, or any General Motors vehicle with this type of eight cylinder engine will be the same. If you drive a different vehicle, the process will be very similar and the photos will act as a great guide through the process. 

You can order an ignition control module for your vehicle on Amazon. They have a great parts lookup system to be sure you get the right one for your engine.

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Removing Parts to Access the ICM

air filter assembly
Removing the air filter assembly to access the distributor. John Lake

The first thing that needs to be removed to access the distributor is the air cleaner assembly. To remove this, there are a couple of connections that need to come off first. There is a breather hose attached underneath toward the front of the engine compartment. This pulls off easily. Next, remove the larger preheat tube from the bottom of the air cleaner. This should also pull right off, although it might be a little stuck from being on there so long. Remove the wing nut from the top of the air cleaner and take off the cover. With the air cleaner element removed you may see a couple of small bolts attaching the air cleaner assembly. If you're not sure, give it a firm tug upward and, if it doesn't pop off or at least shift a lot, you need to remove some bolts first. 

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Accessing and Removing the Ignition Control Module

ICM wiring harness
Remove the wiring from the back of the ignition control module. John Lake

With the air filter assembly removed, you can see the spark plug wires and distributor cap. You will need to remove the distributor cap to access the ignition control module, but do NOT remove all of those plug wires! It's not a necessary step and, if you're anything like me, there's always a real chance that you'll screw up the firing order when you reinstall them and have to go back to square one. Leaving them attached to the distributor cap is a much easier move. Remove the two bolts that attach the cap to the distributor and move the cap to the side. You'll see a black plastic piece of electronics there, this is the module you're looking for. Remove the two electrical plugs on the side, then remove the two screws that are attaching the ICM to the distributor. 

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Applying the Dielectric Grease

dielectric grease
Apply the contact grease to the bottom of the new ICM before installation. John Lake

You're now ready to install the new ignition control module. It's nice and clean, but we need to dirty it up a bit with the dielectric grease. This grease is essential to creating a positive and lasting connection between the ICM and the information it needs from the distributor. The grease was included with your replacement ignition module. Apply a liberal coat, as pictured, before you start the process of installing the module. 

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Reinstallation of Parts

air filter hoses
Reattach the hoses to your air filter assembly. John Lake

Attach the two screws to your new ICM and reinstall the wiring harnesses. Next, reinstall your distributor cap. Aren't you glad you don't have to put all of those plug wires back now? Attach the two screws holding the cap in place. Now put the air cleaner assembly back on (if yours had screws or bolts, put them back, too). Attach the cover of the air filter assembly and tighten the wing nut. Don't forget to replace the two hoses you removed from underneath the assembly. You're done!