How To Test The Ignition Coil Pack -Misfire Troubleshooting Tests (GM 3.8L)

This article presents very simple and effective ON CAR tests of the ignition coil packs on the GM 3.8L V6 equipped engines (Buick, Chevy, Oldsmobile, Pontiac).

You'll be able to troubleshoot and diagnose a BAD ignition coil, or BAD spark plug wires, or a BAD ignition control module as the cause of a misfire condition on your 3.8L V6 equipped GM vehicle.

Now if your car CRANKS but DOES NOT START, you may want to check the Ignition Control Module (ICM) and 3X/18X Crankshaft Position Sensor Tests Article, by clicking here: Testing The Ignition Control Module (ICM) Buick, Chevy, Pontiac, Oldsmobile 3.8L V6 Engines since this article (this one you're reading right now) concentrates on tests when the complaint is that of a vehicle that Starts and Runs but Runs with a misfire Condition.

If you're looking for the article to test the ignition coil packs on the 3.1L and 3.4L V6 GM engines, go here: GM Coil Pack Test (3.1 & 3.4 V-6 Engines).

You can find this tutorial in Spanish here: Cómo Probar las Bobinas de Encendido (GM 3.8L) (at:

Common Symptoms Of A BAD Ignition Coil Pack And/Or Spark Plug Wires

The most common complaint is that your car (or mini-van) will start and run, but run with a misfire. Here are few others symptoms that your car or mini-van may be experiencing:

  1. The check engine light (CEL) will be illuminated on your instrument cluster but not always.
  2. Engine misfire codes:
    1. P0300, P0301, P0302, P0303, P0304, P0305, P0306
  3. Your car will idle rough.
  4. A 'rotten egg' smell may come out of the tailpipe when you drive your car (or mini-van).
  5. Really bad gas mileage.
  6. Your vehicle does not pass the emissions test.

Basic Working Theory Of The 3.8L Ignition Coil Pack

Basic Working Theory of the 3.8L Ignition Coil Pack. How To Test The Ignition Coil Pack -Misfire Troubleshooting Tests (GM 3.8L)

In a nutshell when you turn the key to crank and start your car:

  1. 12 Volts flow into the ignition control module.
  2. This voltage is distributed by the module to the 3 ignition coils sitting on top of it and to the crankshaft position sensor assembly.
  3. Once the engine starts to crank, the crankshaft position sensor starts producing its signals which are sent to the ignition control module (ICM).
  4. When the ignition control module (ICM) receives these crank sensor signals, it starts to create a switching signal for each individual ignition coil pack.
  5. It's this switching signal in combination with 12 Volts that make the ignition coil packs start sparking away.

Each ignition coil sitting on top of the ignition control module (ICM) has two towers. Both towers fire off spark to two different cylinders at the exact same time. It's very important for you to note that the cylinders that get spark from the same ignition coil are called ‘paired cylinders’ in this article.

In case you're wondering what the heck is the switching signal, this term describes the switching On and Off of the Primary Current (12 Volts) that flows thru' the ignition coil by interrupting its path to ground by the ignition control module.

As already mentioned, if both power and the switching signal are present, then the ignition coil has to fire off spark... unless its fried. Testing for these two signals is easy and doesn't require any expensive testing equipment, you don't even need a scan tool. I'm gonna' walk you thru' the whole testing process in detail.