How To Find The Bad Or Clogged Fuel Injector

Finding the bad or clogged fuel injector on your 3.2L Isuzu Amigo (Rodeo, Trooper) can be a challenge. What's gonna' help is to know that whether the fuel injector is clogged or fried, the cylinder that fuel injector feeds with fuel is going to misfire. This misfire will be very noticeable when the engine idles.

Since this misfire will be noticeable when your Isuzu's engine is idling, we can perform a series of tests to find out which cylinder is the one that's being affected. Once the misfiring cylinder has been identified we can find out if the cause is a clogged (or bad) fuel injector (thru' a process of elimination).

Below, I'm sharing with you a simple diagnostic strategy I've used for many years to find the fuel injector that's either clogged or fried (internally).

These are the fuel injector diagnostic test steps:

  1. Find the ‘dead’ cylinder first.
    • If your Isuzu is OBD II equipped, you can easily do this by checking for misfire trouble codes with a scan tool (or code reader).
    • You won't always have a specific bad fuel injector code, but you'll definitely have a misfire code.
    • If no codes are present, or your Isuzu is not OBD II equipped, then the next best thing to do is a cylinder balance test.
    • A cylinder balance test is one of the most effective ways to find a dead cylinder. The following tutorial will help you do a cylinder balance test on the ignition coil pack equipped 3.2L Isuzu engine:
  2. Check the ignition system for spark.
    • After finding the ‘dead’ cylinder, it's important to make sure that each ignition coil is sparking (delivering spark to the spark plug).
    • The following tutorial will help you test the ignition coils on the Coil-On-Plug equipped 3.2L:
    • The following tutorial will help you test the ignition coil packs on the coil pack equipped 3.2L:
    • 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).
  3. Check engine compression.
  4. Noid light test.
    • If every test above checks out OK, then the next step is to do a fuel injector Noid light test.
    • The Noid light test will help you 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).
  1. Swap the fuel injector with its neighbor on the fuel injector rail.
    • I'll swap out the fuel injector with its neighbor only if I have confirmed that:
      1. The ignition system is not at fault.
      2. The cylinder's compression value is good (compared to the rest of the cylinders).
      3. The fuel injector's internal resistance is good.
      4. I think the fuel injector is clogged.
      If the misfire now follows that swap, I now know that fuel injector is clogged (or bad) and needs to be cleaned or replaced.

Finding a bad/clogged fuel injector can be a challenge (especially on the 1992 thru' 1997 SOHC 3.2L Isuzu engines with the fuel injectors under the intake manifold plenum). What will help you save a lot of time, money and frustration is to first find the ‘dead’ cylinder. Following the above diagnostic strategy has saved my lunch quite a few times and I think it'll help you too!

Fuel Injectors Under The Intake Manifold Plenum

On the 1993 to 1997 3.2L Isuzu engines, the fuel injectors aren't very accessible since they're located under the intake manifold plenum.

To explain this a bit further: the intake manifold is made up of two parts. The lower part is called the intake manifold (or lower intake manifold). The upper part is called the intake manifold plenum (or upper intake manifold).

To gain access to the fuel injectors (particularly injectors for cylinders #2, #4, and #6) on the 1993 thru' 1996 3.2L Isuzu engines, the upper intake manifold plenum must be removed.

If you're faced with having to remove the intake manifold plenum, to test the fuel injectors, keep the following suggestions in mind:

  • As you remove bolts, nuts, and/or any small parts, place all them in a container and away from the engine. This will help you avoid having anything fall into the open intake manifold runners that will be exposed once the plenum is removed.
  • Immediately cover the open lower intake manifold runners with clean shop towels once you have removed the upper intake manifold plenum. The purpose of stuffing these shop towels into the open intake runners is to keep any foreign metal object from falling into them.
  • When installing new intake plenum gaskets, don't coat them in any type of sealer (like RTV Silicon Gasket Sealer). Using a gasket sealer on these gaskets (that are installed ‘dry’) could back fire on you and provoke a vacuum leak down the road.

Anything that falls into an open intake manifold runner will usually end up inside an engine cylinder. If any metal part (like a bolt, washer, or a nut) falls in and you start the engine, you're going to be in a world of hurt!

The engine is gonna' knock like it threw a rod! Not only that, but whatever fell in will damage the cylinder head valves and/or piston top. The only way to remove whatever fell in, is to remove the engine's cylinder head. This is something you want to avoid!

Removing the intake manifold plenum on the 3.2L V6 Isuzu engine can be done successfully and without complications if you follow a repair manual and follow the suggestions above.

More 3.2L Isuzu Diagnostic Tutorials

You can find a complete list of 3.2L Isuzu tutorials in this index: Isuzu 3.2L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

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Isuzu Vehicles:

  • Amigo 3.2L
    • 1999, 2000
  • Rodeo 3.2L
    • 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003
  • Trooper 3.2L
    • 1992, 1993, 1994, 1995, 1996, 1997

Honda Vehicles:

  • Passport 3.2L
    • 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002