How To Find The Bad Or Clogged Fuel Injector

Quite a few things can cause an engine cylinder misfire and of course a bad or clogged fuel injector is of them.

The key to finding the cause of the problem (whether it's a bad or clogged injector or not), is to eliminate the components that are involved in providing spark, air, and fuel to the ‘dead’ cylinder or cylinders.

In case you're needing a little more guidance on the matter, I'll explain how to do this in the troubleshooting steps below.

OK, these are the steps I take:

  1. Find the ‘dead’ cylinder first.
    1. 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 car's PCM's memory.
  2. Make sure that the ‘dead’ cylinder's fuel injector connector and COP ignition coil connector are not broken.
    1. Broken fuel injector and ignition coil connectors are a very, very, very common problem on the 1999-2000 4.6L Ford engines.
    2. If you do find broken connectors, then you've probably have found the source of the misfire.
  3. After identifying the ‘dead’ cylinder, make sure it's getting spark.
    1. It's important that you check the cylinder's Coil-On-Plug (COP) ignition coil for spark with a dedicated spark tester.
      1. The following tutorial will help you to test the COP ignition coils: Coil-On-Plug (COP) Ignition Coil Misfire Tests (Ford 4.6L, 5.4L).
    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).
  4. 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).
  5. 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).
  6. 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.

Thank You For Your Donation

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

If This Info Saved the Day, Buy Me a Beer!