How To Test The Fuel Injectors (1999-2000 1.8L Mazda Protegé)

How To Find The Bad Or Clogged Fuel Injector

Finding out if a fuel injector is the cause of your engine performance troubles is not that hard. Especially because all of the components, that need to checked on your 1.8L Mazda Protegé, are within easy access.

Also, I can tell you from personal experience that there is a logical starting point and a logical step by step process to finding the bad or clogged fuel injector.

Below, I am going to explain how I do it. Alright, these are the test steps I follow:

  1. Find the ‘dead’ cylinder first.
    • This is the most important first step. Finding the dead cylinder is as easy as connecting a scan tool or a code reader and reading the specific misfire code that your 1.8L Protegé's fuel injection computer has stored in its memory.
  2. After identifying the ‘dead’ cylinder, make sure it's getting spark.
    1. To get the most accurate test result, it's important that you use a dedicated spark tester to check for spark. Otherwise, using any other method may have you chasing after ghosts.
    2. The next step is to make sure that the spark plugs and spark plug boots are not swimming in oil from a bad valve cover gasket.
    3. You should also remove the spark plugs and check them for cracks or carbon tracks (this is SO important).
  3. If the ‘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
      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 then I now know that fuel injector is clogged (or bad) and needs to be cleaned or replaced.

The above list of tests may seem like a complicated diagnostic strategy. But it really isn't when you consider the fact that all of the components that need to be tested are easy to access. Also, eliminating these components (as bad) will save you money, frustration, and time as you avoid replacing parts your car doesn't need.

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