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How To Find The Bad Or Clogged Fuel Injector
Quite a few things can cause an engine cylinder to misfire, and of course a bad or clogged fuel injector is one of them.
The key to finding the source of the problem (whether or not it is a bad or clogged injector) is to eliminate the components involved in providing spark, air and fuel to the 'dead' cylinder or cylinders.
In case you need a little more guidance on this topic, I'll explain in the troubleshooting steps below.
OK, these are the steps I take:
- Find the '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 vehicle's PCM memory.
- Make sure the 'dead' cylinder's fuel injector connector and COP ignition coil connector are not broken or damaged.
- Broken fuel injector and ignition coil connectors are a very, very, very common problem on the 1999-2000 4.6L Ford engines.
- If you find broken connectors, you've probably have found the source of the misfire.
- After identifying the 'dead' cylinder, make sure it's getting spark.
- It's important that you check the cylinder's Coil-On-Plug (COP) ignition coil for spark with a dedicated spark tester.
- 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).
- It's important that you check that the spark plug boot and spark plug are NOT soaked (or swimming) in engine oil.
- 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).
- It's important that you check the cylinder's Coil-On-Plug (COP) ignition coil for spark with a dedicated spark tester.
- If the 'dead' cylinder has spark, the next step is to make sure it has good compression.
- After making sure that the 'dead' cylinder's plug wire is delivering spark, you need to check for low engine compression.
- This is one of the most overlooked tests when diagnosing a misfire or rough idle condition. You can find the test here:
- 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).
- If the 'dead' cylinder has spark, good compression, and is being activated; the next step is swap the fuel injector.
- If I've found out that I have a specific 'dead' cylinder and:
- The ignition system is not at fault.
- That cylinder's compression value is good (compared to the rest of the cylinders).
- The fuel injector resistance is good and is being activated by the fuel injection computer.
- I think the fuel injector is clogged, I then swap out that fuel injector with its neighbor.
- If I've found out that I have a specific 'dead' cylinder and:
As you can see, finding the cause of the misfire boils down to a process of elimination. Once you've identified the 'dead' cylinder, the next steps are to make sure it's getting spark, good compression, etc.

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