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:
- Misfire codes: P0301, P0302, P0303, P0304
- Misfire with check engine light (CEL) ON.
- Misfire with check engine light (CEL) OFF. In other words, the car is experiencing a bona-fide 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!
- Car cranks, starts and runs but runs BAD.
- Engine has no power when you accelerate the vehicle.
What Tools Do I Need?
- 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.
- 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.
- Three used spark plugs.
- Test Light.
- 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 clic here: Abe's LED Light Test Tool
- 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 Diagnostics 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 distributorless 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:
- The crankshaft position sensor starts to generate its signal, which is sent directly to the ignition control module (ICM).
- 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.
- 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).
- 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.
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:
- If you don't have an HEI spark tester buy one.
- Do not accept imitations or similar tools.
- 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.