How To Test The Ignition Coils (GM 2.4L Quad 4)

Testing the Quad 4 (2.4L) GM ignition coils can be a bit of a challenge since they're located under an aluminum cover. Also, in my humble opinion, this ignition system is not the most sturdy or well thought-out way to create and deliver spark to the engine cylinders. In any other GM ignition system, you're able to isolate most of the major components to test them individually (and while on the car), but not the Quad 4 ignition system.

This doesn't mean that it can't be tested but it does complicate things a bit. In this article, I'm gonna' present to you my way of doing it using some pretty simple tools.

This method has worked for me ever since the Quad 4 was introduced way back in the late 80's. Before you dive into the tests, I recommend that you read the entire article first.

This article only covers testing for a misfire where the car starts and runs. So if your car CRANKS BUT DOES NOT START, and you need to test the Quad 4 ignition control module (ICM) or its crankshaft position (CKP) sensor go here: Testing the 2.4L Quad 4 Ignition Control Module.

You can find this tutorial in Spanish here: Cómo Probar las Bobinas De Encendido (GM 2.4L Quad 4) (at: autotecnico-online.com).

Symptoms Of A Bad Ignition Coil

The most common symptoms (when you have a bad ignition coil) are, but not limited to:

1. Misfire codes: P0301, P0302, P0303, P0304.
2. Misfire with check engine light (CEL) ON.
3. Misfire with check engine light (CEL) OFF. In other words, the car is experiencing a bonafide misfire that should light up the check engine light and should set a specific cylinder misfire code, but it doesn't. But then again, what the hell is a misfire code good for anyway?? It could be caused by a different number of things that may have nothing to do with the ignition system!
4. Car cranks, starts and runs but runs bad.
5. Engine has no power when you accelerate the vehicle.

What Tools Do I Need?

1. HEI spark tester.
   • This is a MUST HAVE tool to be able to use the info in this article and successfully diagnose the ignition coils on your Quad 4 engine.
   • You can buy this tool online (don't have an HEI spark tester? Need to buy one? You can buy it here: OTC 6589 Electronic Ignition Spark Tester).
   • Click here to see what this tool looks like: The HEI Spark Tester.
2. Two sets of battery jumper cables.
   • These are also MUST HAVE tools to be able to use the info in this article and successfully diagnose the ignition coils on your Quad 4 engine.
3. Three used spark plugs.
4. 12 Volt test light.
5. LED light.
   • You can buy one at any auto parts store (like AutoZone, O'Reilly, Pepboys, etc.) or at any electronics store (like Radio Shack - this is where I buy mine).
   • To see what this tool looks like click here: Abe's LED Light Test Tool
6. Multimeter.
7. Repair manual.
   • This book will come in handy to answer any 'how to remove and replace' question that this article doesn't answer.

A scan tool (automotive diagnostic scanner) is not needed to test the ignition coils. The tests that you're about to learn are all done without a scan tool.

Basic Operating Theory

This type of distributor-less ignition system uses two ignition coils and each fires spark to two different cylinders simultaneously. One ignition coil feeds spark to cylinders 1 and 4 and the other one feeds cylinders 2 and 3 with spark.

This type of ignition system is known as a Waste Spark ignition system. I won't go into detail about it (Waste Spark), since this info is not that important to diagnose the car (unless you want to reverse engineer the ignition system or something). But if you do want more info on it, you can Google it.

OK, what you really need to know is that when you turn the key to crank the engine, this is what happens:

1. The crankshaft position sensor starts to generate its signal, which is sent directly to the ignition control module (ICM).
2. When the module receives this signal, it converts it into a digital signal (called the 7X REFERENCE SIGNAL) that is sent to the fuel injection computer.
3. When the computer receives this 7X REFERENCE SIGNAL, it does its little song and dance and shoots back two separate signals to the ignition control module (ICM).
4. These two signals (called IC Signals in most of the service literature) are the ones the ignition module needs to activate the ignition coils to start sparking.

As you can see, it's all pretty straightforward, the only thing that complicates the testing is that the ignition coils are hidden under the aluminum cover and inside a plastic container called the ignition coil cover.

Again, in this article we're only gonna' concentrate on testing the ignition coils only, so if you need to test the crankshaft position sensor or the ignition control module go here: Testing The 2.4L Quad 4 Ignition Control Module.

Where To Buy The Ignition Coil And Save

The following links will help you comparison shop the original equipment AC-Delco (Delphi) ignition coil:

Do's and Don'ts When Testing For Spark

The very first test that I'm gonna' ask you to do is a spark test. This is the most important part of the whole procedure, so please take a moment to read the following suggestions:

Most of the components that you may end up replacing are not cheap. The last thing that you want to add to the frustration of having to repair you car, is to throw money down the drain by replacing parts that the car doesn't need. By using the wrong tools to diagnose your Quad 4 ignition coils you'll end up doing exactly that.

Here are some of my recommendations for when testing for spark:

1. If you don't have an HEI spark tester buy one.
2. Do not accept imitations or similar tools.
3. Do not use a spark plug instead of the HEI spark tester unless otherwise indicated in this article.
   • You may have read somewhere that using a regular spark plug to test for spark is acceptable. Nothing could be further from the truth.
   • Want to guarantee a false result from your spark test that'll have you wasting time and money? Well then, use a regular spark plug instead of an HEI spark tester.

Using the wrong spark tester for the spark test on the Quad 4 engine is akin to trying to eat a bowl of soup with a fork.

TEST 1: Testing For Spark

The first part and the most important, is to find out which cylinders are not getting spark. I'm going to show you a very specific method to do this.

To be a bit more specific, we're gonna' make sure that each ignition coil cover boot is firing off spark. This will require a very unusual test (see photo above). I can tell you from personal experience that doing it this way will help you find the ignition system problem causing the misfire without having to guess at it.

Read this entire section before starting out, and as stated in the previous page, it's very important that you use an HEI spark tester where one is called for.

IMPORTANT: In the photo above you'll notice that all of the boots are labeled with a number. This number is the cylinder number to which this boot belongs to. I've included this info because you'll need to know the number of the cylinder to interpret your test results correctly.

OK, let's get this show started:

1. Remove the top engine aluminum cover that contains the coil pack/ignition module assembly.
   
   If the plug boots stay stuck to the spark plugs, remove them and connect them to the coil cover.
2. Re-connect the ignition module to its connector, if you had to unplug it from its connector to remove the aluminum cover from the engine.
3. Connect the HEI spark tester to spark plug boot #1.
4. Connect a regular spark plug to the remaining three spark plug boots (#2, #3, #4).
5. Ground the spark tester and each spark plug with a battery jump start cable.
   
   Connect the other ends of the battery jump start cables to a good Ground point.
6. Have your assistant crank the engine while you observe the HEI spark tester.
   
   No need to pay attention to whether the other spark plugs spark or not that are attached to the other boots.
   
   IMPORTANT: The spark plugs and HEI spark tester must be completely attached to the spark plug boots. What sometimes make this difficult is if the boots have engine oil inside of them. This oil will make the spark plugs or the HEI spark tester you've attached pop out when you start cranking the engine. Take whatever actions to avoid this from happening.
7. Remove the HEI spark tester from boot #1 connect it to boot#2. Now connect the spark plug that was in boot #2 to boot #1. Ground both with the jump start cables.
8. Have your assistant crank the engine again. The spark tester should spark.
9. Repeat the spark test with the HEI spark tester on the remaining spark plug boots.

Let's take a look at what your test results mean:

CASE 1: Got NO SPARK from only one spark plug boot. This test result tells you that the ignition coil that feeds that boot is bad.

The next step is to identify the ignition coil. For this go to: TEST 2: No Spark From Only One Boot.

CASE 2: Got NO SPARK from spark plug boot 1 and 4. These two cylinder get spark from the same ignition coil.

The next step is to make sure that the ignition module is activating this ignition coil to spark. For this test go to: TEST 3: No Spark From Two Boots That Feed Paired Cylinders.

CASE 3: Got NO SPARK from spark plug boot 2 and 3. These two cylinder get spark from the same ignition coil.

The next step is to make sure that the ignition module is activating this ignition coil to spark. For this test go to: TEST 3: No Spark From Two Boots That Feed Paired Cylinders.

CASE 4: Got NO SPARK from two different spark plug boots that are not 1 and 4 or 2 and 3. Go to: TEST 4: No Spark From Two Boots That Are NOT Paired Cylinders.

CASE 5: Got spark on ALL spark plug boots. This is the correct and expected test result.

This test result usually tells you that the ignition system is OK and not behind the misfire. For more testing suggestion, go to: TEST 5: You Got Spark From All Boots.