How To Test The Fuel Injectors (1997-2002 4.6L Ford F150, F250)

How To Find The Bad Or Clogged Fuel Injector

Being able to pinpoint the exact fuel injector that has failed is a time and money saver. Why? Because you avoid the frustration of replacing something your Ford pickup or van doesn't need and that did not solve the problem.

Over the years, I found a method to find the bad or clogged fuel injector that I've used with a lot of success. This method involves a process of elimination that will nail down the exact cause of the misfire whether it's a failed/clogged fuel injector or not. In this section, I'm going to share it with you:

1. 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 car's PCM's memory.
2. Check that the misfiring cylinder's fuel injector connector is not broken or damaged.
   • Broken or damaged fuel injector connectors are a very, very common problem on the 4.6L Ford engine.
3. After identifying the ‘dead’ cylinder, and that its fuel injector connector is OK, make sure it's getting spark.
   • It's important that you check the tower (of the ignition coil pack assembly) for spark with a dedicated spark tester.
   • 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.
   • If your 4.6L Ford engine is equipped with Coil-On-Plug (COP) ignition coils, check that the ignition coil's connector isn't broken. The ignition coil's connector's locking tab breaks very easily. This will result in a misfire as the connector makes a false contact with the ignition coil.
4. 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:
     • How To Check The Engine Compression (Ford 4.6L, 5.4L) (at: troubleshootmyvehicle.com).
5. 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).
6. 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:
     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.

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