How To Test Misfire Codes (GM 2.3L, 2.4L Quad 4)

How Can I Test The Misfire?

Now that you have an idea of what are some of the causes of a misfire condition, you might be asking yourself, ‘Where should I start?’.

In this section, I'm gonna' offer you a simple diagnostic strategy that should help you find and resolve the root cause of the misfire or ‘dead’ cylinder on your Quad-4 equipped GM vehicle.

STEP 1: Identify the dead cylinder. This is the most important first test that will save you a lot of time and frustration down the road by narrowing down and focusing your misfire diagnostic.

Finding the dead cylinder usually entails connecting your scan tool to your vehicle and reading the misfire diagnostic trouble codes. Then by matching the misfire code to its engine cylinder using an illustration of the engine cylinders.

Now, the PCM doesn't always set a specific cylinder misfire code. This is when knowing how to do and interpret a manual cylinder balance test comes in handy. In a nutshell, a manual cylinder balance test involves unplugging one injector at a time (to see which one has NO effect on the engine's idle).

The fuel injector that does not worsen the engine's idle when unplugged tells you that that specific cylinder is ‘dead’.

You can find a step-by-step tutorial on how to do a manual cylinder balance test here:

• How To Do A Cylinder Balance Test (GM 2.3L, 2.4L Quad 4).

STEP 2: Test the ignition system . Once you have identified the dead cylinder, the next step is to check that all 4 spark plugs are getting spark since the majority of misfires are caused by a failed component in the ignition system. You should:

1. Perform a spark test (using a dedicated spark tester) on the spark plug wire of the cylinder that the misfire code is accusing of being dead.
   • Testing for spark with a spark tester is the most important first test since you'll know right away if the misfire is due to a lack of spark.
2. Check to see if the spark plug boots and spark plugs are swimming in engine oil from a leaking valve cover gasket.
3. If you got spark from your spark tester (from the cylinder the misfire code is accusing of misfiring), the next step is to remove the spark plug or spark plugs (of the affected cylinders) and check them for wear and tear, carbon tracks, anti-freeze, etc.
4. If you get no spark, then the next step is to check for spark directly on the ignition coil pack tower.
5. You can find all of these ignition system tests here:
   • How To Test The Ignition Coils GM 2.4L Quad 4 (at: easyautodiagnotics.com).
   • Diagnosing A Bad Ignition Coil Quad 4 Case Study (at: easyautodiagnotics.com).

STEP 3: Test the fuel injectors. If the ignition system is not the cause of the misfire, then the next step is to check the fuel injectors.

You'll need to:

1. Resistance test each of the 4 fuel injectors.
2. Do a Noid light test of each one to make sure the PCM is pulsing them (activating them).
3. You can find the fuel injector tests here:
   • How To Test The Fuel Injectors (GM 2.4L Quad 4).

STEP 4: Test the compression of each engine cylinder. Other tests that should be done, if the ignition system and fuel injectors check out OK are:

1. Engine compression test.
2. Checking for vacuum leaks.
3. You can find the engine compression test here:
   • How To Test Engine Compression (GM 2.4L Quad 4).

The above list of steps may seem/sound like troubleshooting a Misfire is a complicated thing but it really isn't. Depending on your level of ‘wrenching’ experience, this is something that you can accomplish without taking it to the shop.

What Tools Do I Need To Test The Misfire Code(s)?

Finding the exact cause of the misfire codes or misfire condition is possible with the proper tools. Without them, you won't be able to diagnose/troubleshoot those issues on your Quad-4 equipped GM car.

Depending on what the root cause of the misfire is, you may need several tools. Most of these you can buy online, none of these will break the bank and I'll make some recommendations on them. Here's a guide to some of the basic tools that can be and are used:

1. Ignition System Tests:
   • Spark tester.
   • Multimeter.
   • Test light.
2. Fuel System Tests:
   • Noid light.
   • Fuel pressure gauge.
   • Multimeter.
3. Engine Mechanical Tests:
   • Compression tester.

Now of course, you'll also need basic hand tools like: screw-drivers, ratchet wrenches, sockets, etc. You'll also need a generic scan tool to retrieve the diagnostic trouble codes (DTCs) from the computer's memory.

Keep in mind that using the right tool for the job will save you time, frustration, and /or keep you from damaging the component that you're testing.

More Quad-4 Tutorials

You can find a complete list of Quad-4 troubleshooting tutorials here: GM 2.4L Index Of Articles.

Here's a sample of the tutorials you'll find in the index:

• How To Troubleshoot A No Start (GM 2.3L, 2.4L Quad 4).
• How To Test For A Blown Head Gasket (GM 2.4L Quad 4).
• How To Test Engine Compression (GM 2.4L Quad 4).
• How To Test The MAP Sensor (GM 2.4L Quad 4).
• How To Test The GM EGR Valve Buick, Chevy, Olds, Pontiac (at: easyautodiagnotics.com).
• How To Test The GM 2.4L Throttle Position Sensor (TPS) (at: easyautodiagnotics.com).
• How To Test The Ignition Coils GM 2.4L Quad 4 (at: easyautodiagnotics.com).
• Diagnosing A Bad Ignition Coil Quad 4 Case Study (at: easyautodiagnotics.com).