How To Test The Fuel Injectors (1999-2001 1.6L Mazda Protegé)

How To Find The Bad Or Clogged Fuel Injector

Diagnosing a bad or clogged fuel injector can seem like a big challenge. I can tell you that if you know where to start, finding it (the bad or clogged fuel injector) is not that hard.

In this section I'm going to show you the step-by-step process I use myself to find the faulty injector or eliminate the four of them as bad. I think you'll see that there is a method to the madness.

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

  1. Find your Mazda Protegé's ‘dead’ cylinder first.
    • This is the most important first step. You can do this by connecting a scan tool (or code reader) and identifying the specific misfire code that's registered in your Mazda's PCM's memory.
  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).
  3. If your Protegé's ‘dead’ cylinder has spark, 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:
  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 and I think the fuel injector is clogged; I then swap out that fuel injector with its neighbor.
      If the misfire now follows that swap then 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 1.6L Mazda 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!

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Mazda Vehicles:

  • Protegé 1.6L
    • 1999,