How To Find The Bad Fuel Injector

There was a time when having to diagnose a defective fuel injector on the 3.0L Ford Taurus (Mercury Sable) made me very nervous. Especially because 3 of the 6 fuel injectors are located underneath the intake manifold plenum (and you've got to remove this bad boy to be able to access them).

Thankfully I was able to develop a strategy of tests that helped me speed up the process of finding the defective or clogged fuel injector (although in a lot of cases, the cause of the engine misfire had nothing to do with a defective or clogged fuel injector).

Okay, this is the basic diagnostic strategy that I used and I think will prove helpful to you too:

  1. Identify the dead cylinder first.
    1. This means that you will have to do a manual under balance test to find the misfiring cylinder.
  2. Verify that the dead cylinder is getting spark.
    1. To get the most accurate test result, it's important that you use a dedicated spark tester for this test.
    2. You also need to remove the spark plug and check that it is not damaged in any way shape or form.
    3. Make sure that the spark plug boot is not damaged or covered in a carbon track. You can find out more about carbon tracks here: Carbon Tracks Are A Common Cause Of Ignition Misfires.
    4. The idea here is to make sure that the ignition system is not behind misfire problem.
  3. Once you've confirmed that the dead cylinder is getting spark then the next step is to make sure that it has good compression.
    1. This tutorial will help you with the compression test and more importantly, how to interpret its test results: How To Do And Interpret an Engine Compression Test (Ford 3.0L, 3.8L).

Once I had confirmed that the dead cylinder was getting spark and that it's compression was good, then I could start worrying about testing the fuel injector (to see if it was fried or if it was clogged). But the principal idea here is that you should first locate the dead (misfiring) cylinder before you do any type of testing.

The Intake Manifold Plenum Has To Be Removed

How To Test The Fuel Injectors (1991, 1992, 1993, 1994, And 1995 3.0L Ford Taurus)

I'm pretty sure that you've noticed by now that the intake manifold plenum covers 3 of the 6 fuel injectors on the 3.0L V6 Ford Taurus engine. These fuel injectors are the ones for cylinders 1, 2, and 3. Yup, you're gonna' have to remove the intake manifold plenum to access them.

Having done this job quite a few times myself, here is a list of suggestions that will help you avoid any complications or headaches:

  1. Once you remove the plenum and the lower intake manifold ports are exposed, make sure that nothing (like a bolt or a washer or any other metal component) falls into them.
  2. As you're removing bolts (or nuts), place them in a container that's located away from the engine compartment.
  3. Once you've removed intake manifold plenum, place clean shop towels over the lower intake manifold ports.

If anything falls into any one of the 6 ports of the lower intake manifold, and you start the engine -you're gonna' be in a world of hurt. The only way to remove whatever fell into the engine is to remove the cylinder head (or heads). Also, the engine can suffer piston or cylinder head valve damage as the metal object bounces around the cylinder.