How To Find The Bad Or Clogged Fuel Injector

One of the most important things to remember, is that whether the fuel injector has shorted internally or is just clogged, it will cause a misfire. This misfire will lead to a misfire trouble code that will light up your Crown Victoria's check engine light.

This also means that the same troubleshooting process can be applied to finding either a failed or clogged fuel injector. How do I know? From the results of my personal experience as an automotive technician.

I can also tell you that finding the bad or clogged fuel injector is not hard because most of the components that need to be tested (in order to be eliminated as a source of the misfire) on your 4.6 liter Crown Victoria are very easy to get to and in plain view.

OK, this is my troubleshooting method:

  1. Find the ‘dead’ cylinder first.
    1. By dead cylinder, I mean the misfiring cylinder. This is the most important first step and can not be overlooked. You can do this by connecting a scan tool (or code reader) and identifying the specific misfire code that's registered in your car's PCM's memory.
  2. After identifying the ‘dead’ cylinder, make sure it's getting spark.
    1. It's important that you check the tower (of the ignition coil pack assembly) 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).
      1. 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 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:
      1. How To Test Engine Compression (Ford 4.6L, 5.4L).
  4. If the ‘dead’ cylinder has spark and good compression, the next step is a fuel injector Noid light test.
    1. If every test above checks out OK, then the next step is to make sure that the fuel injector is being activated.
    2. 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.

As you can see, finding the cause of the misfire boils down to a process of elimination. As you start off by identifying the ‘dead’ cylinder, the next steps are too make sure that its getting spark, good compression, etcetera.

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