How To Test The Fuel Injectors (2008-2010 GM 2.4L)

How To Find The Bad Or Clogged Fuel Injector

Having work on cars for a long time as a professional technician, I came up with a very simple method of locating a bad or clogged fuel injector. This method proved so effective that I was able to either condemn a fuel injection rule it out with in about 98% of the cases. In this section I am going to explain it to you in a step-by-step way

When I need to find the bad or clogged fuel injector, this is what I do:

1. Find the ‘dead’ cylinder first.
   • This step can not be skipped or overlooked. What makes it easy to find the ‘dead’ cylinder is the fact that your vehicle's PCM will set a specific misfire code identifying it (P0301, P0302, P0303, or P0304).
   • In some cases it might even set a fuel injector trouble code: P0201, P0202, P0203, or a P0204
2. After identifying the ‘dead’ cylinder, make sure it's getting spark.
   1. It's important that you check for spark with a dedicated spark tester.
   2. It's important that you check that the spark plug boot and spark plug are NOT soaked (or swimming) in engine oil.
   3. You should also remove the spark plugs and check them for cracks or carbon tracks (this is SO important).
      • Here's a real life case study on carbon tracks and how they can cause a Misfire: Carbon Tracks Are A Common Cause Of Ignition Misfires (at: easyautodiagnostics.com).
3. If the ‘dead’ cylinder's ignition coil is sparking, the next step is to make sure it has good compression.
   1. After making sure that the ‘dead’ cylinder's plug wire is delivering spark, you need to check for low engine compression.
   2. This is one of the most overlooked tests when diagnosing a misfire or rough idle condition. You can find the test here:
      • How To Test Engine Compression (GM 2.4L Quad 4) (this tutorial will apply to your 2.4L Ecotec engine).
4. If the ‘dead’ cylinder has spark and good compression, the next step is a fuel injector Noid light test.
   • If every test above checks out OK, then the next step is to make sure that the fuel injector is being activated.
   • The following Noid light article/tutorial may help you: How To Use A Noid Light And Where To Buy It (I know that this is not the most in-depth article on the subject, but it should give you an idea of what is involved).
5. If the ‘dead’ cylinder has spark, good compression, and is being activated; the next step is swap the fuel injector.
   1. If I've found out that I have a specific ‘dead’ cylinder and:
      1. The ignition system is not at fault.
      2. That cylinder's compression value is good (compared to the rest of the cylinders).
      3. The fuel injector resistance is good and is being activated by the fuel injection computer...
      4. I think the fuel injector is clogged, I then swap out that fuel injector with its neighbor.
      If the misfire now follows that swap, I now know that fuel injector is clogged (or bad) and needs to be cleaned or replaced.

Finding the bad/clogged fuel injector can be a challenge on your 2008-2010 2.4L Ecotec but it's doable. What will help you save a lot of time, money and frustration is to first find the ‘dead’ cylinder. Following the above diagnostic strategy has saved my lunch quite a few times and I think it'll help you too!

If this info saved the day, buy me a beer!