Should I Test Only One Injector Or Do I Test Them All?

Since the fuel injectors are easy to get to (on all 2.4L Quad 4 equipped GM cars), it's a good idea to test all four, but this is not mandatory.

For example, let's say that you think that the cylinder #1 fuel injector is bad and you only want to test this one. Well, since sometimes the repair manual does not give you a specific resistance value to compare to you'll need to test at least two other fuel injectors to get some values to compare to.

Now, if you do have the correct fuel injector resistance value (from an authoritative source, like a repair manual), then you can only test just that one fuel injector.

Fuel Injector Troubleshooting Guide

If you think you have a bad fuel injector but aren't quite sure where to start, in this section I'm gonna' offer you my fuel injector troubleshooting procedure. The following guide will help you get to the bottom of the problem, whether it's caused by a bad fuel injector or something else.

OK, the most important thing you need to do is identify the ‘dead’ cylinder. Because if you do have a bad fuel injector on your hands, your GM 2.4L Quad 4 equipped vehicle will have a misfiring cylinder.

These are the steps I take:

  1. To find the ‘dead’ cylinder -Check for misfire codes or do a cylinder balance test.
    1. Unfortunately, the PCM usually doesn't set a specific bad fuel injector code, but when a fuel injector does go bad, you WILL see a misfire code.
    2. The idea here is to find the ‘dead’ cylinder. Now, if you have no misfire codes and yet the engine in your GM 2.4L Quad 4 equipped vehicle is misfiring, then you need to do a manual cylinder balance test.
    3. A cylinder balance test involves disconnecting one fuel injector at a time, while the engine is running, to see which one (when disconnected) has NO EFFECT on the engine's idle. The one, when unplugged, that doesn't cause the engine's idle to get worse is the one that belongs to the ‘dead’ cylinder.
    4. The following tutorial will guide you step-by-step thru' the whole procedure:
      1. How To Do A Cylinder Balance Test (GM 2.3L, 2.4L Quad 4).
  2. The next step is to check for spark.
    1. It's very important to eliminate the ignition system as the root cause of the misfire or ‘dead’ cylinder.
    2. What I'm looking for here is that spark is actually reaching the spark plug. This is accomplished using a dedicated spark tester on the spark plug wire.
    3. The following tutorials will guide you step-by-step thru' the whole procedure:
      1. How To Test The Ignition Coils GM 2.4L Quad 4 (at: easyautodiagnostics.com).
      2. Diagnosing A Bad Ignition Coil Quad 4 Case Study (at: easyautodiagnostics.com).
  3. Next, I remove the spark plugs and visually inspect them.
    1. What I'm checking for are for cracks and/or carbon tracks and/or oil filling up the spark plug well.
    2. I also check that the plastic ignition coil cover isn't cracked (due to the engine's heat) and that it doesn't have any carbon tracks.
  4. If everything above checks out OK, I then do an engine compression.
    1. This is a fast and easy test but is so often overlooked.
    2. You can find this test here: How To Test Engine Compression (GM 2.4L Quad 4).
  5. Check fuel injector resistance.
    1. I also do a fuel injector Noid light test to make sure that the fuel injector (that belongs to the ‘dead’ cylinder) is getting power and the activation signal from the fuel injection computer.
    2. Since the fuel injectors are pretty easy to get to, I have also swapped them out to see if the misfire condition moves to the fuel injectors new location (as checked by the manual cylinder balance test).

The purpose of all of the my tests (above) are to eliminate the ignition system and engine mechanical condition first before attempting to blame or suspect a bad fuel injector.

And I can tell you that this diagnostic strategy has saved me from replacing some good fuel injectors and being able to nail down the ones that are bad.

More 2.4L Quad 4 Tutorials

There are several more ‘how to’ tutorials that I've written that are 2.4L Quad 4 specific, that may be of further help. You can find them here: GM 2.4L Index Of Articles and at:

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

  1. How To Test For A Blown Head Gasket (GM 2.4L Quad 4).
  2. How To Test Engine Compression (GM 2.4L Quad 4).
  3. How To Test The MAP Sensor (GM 2.4L Quad 4).
  4. GM 2.4L (Quad 4) Index Of Articles (at: easyautodiagnostics.com).
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Buick Vehicles:

  • Skylark 2.3L, 2.4L
    • 1994, 1995, 1996, 1997, 1998

Chevrolet Vehicles:

  • Cavalier 2.3L, 2.4L
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002
  • Malibu 2.4L
    • 1997, 1998, 1999

Oldsmobile Vehicles:

  • Achieva 2.3L, 2.4L
    • 1994, 1995, 1996, 1997, 1998
  • Alero 2.4L
    • 1999, 2000, 2001

Pontiac Vehicles:

  • Grand Am 2.3L, 2.4L
    • 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001
  • Sunfire 2.4L
    • 1996, 1997, 1998, 1999, 2000, 2001, 2002