How To Test The Fuel Injectors (3.2L Isuzu Amigo, Rodeo, Trooper)

How To Find The Bad Or Clogged Fuel Injector

Locating the faulty or clogged fuel injector on your 3.2L Isuzu Amigo (Rodeo, Trooper) can be a challenge. What will help is to know that whether the fuel injector is clogged or fried, its cylinder will misfire. This misfire is very noticeable when the engine is idling.

As these misfires are noticeable when your Isuzu's engine is idling, we can perform a series of tests to find out which cylinder is affected.

Once the misfiring cylinder has been identified, we can use a process of elimination to figure out if its fuel injector is clogged or fried.

Below, I'll share with you a simple diagnostic strategy I've used for many years to find the fuel injector that is either clogged or internally fried.

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.
  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 by the fuel injection computer.
    • 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.

Locating a bad/clogged injector can be a challenge (especially on the 1992 thru 1997 3.2L SOHC Isuzu engines where the injectors are located under the intake manifold plenum). What will help you save a lot of time, money, and frustration is finding the "dead" cylinder first. Following the diagnostic strategy above has saved my lunch a number of times, and I think it will help you too!

Fuel Injectors Under The Intake Manifold Plenum

On the 1993 thru 1997 3.2L Isuzu engines, the injectors aren't easily accessible as they are located under the intake manifold plenum.

To explain this a little more: The intake manifold consists 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 access the fuel injectors (particularly the injectors for cylinder #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 the need to remove the intake manifold plenum to test the fuel injectors, consider the following suggestions:

  • When removing bolts, nuts and/or small parts, place them all in a container and away from the engine. This will prevent anything from falling into the open and exposed intake manifold runners when the plenum is removed.
  • Cover the opened lower intake manifold runners with clean rags immediately after removing the upper intake manifold plenum. The purpose of tucking these shop towels into the open intake runners is to prevent metal debris from falling in.
  • When installing new intake plenum gaskets, don't coat them in any type of sealant (such as RTV Silicon Gasket Sealer). Using a gasket sealant on these gaskets (which are installed 'dry') could backfire on you and create a vacuum leak down the road.

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

The engine will knock like it threw a rod! Not only that, but whatever falls in will damage the cylinder head valves and/or the top of the piston. Whatever ends up in the cylinder can only be removed by removing the engine's cylinder head. You want to avoid that!

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