How to Test a BAD Fuel Injector (1999, 2000 1.8L Mazda Protegé)

As your 1999-2000 1.8L Mazda Protegé starts to age, sooner or later it will have a fuel injector fail or get clogged. In either of these cases, the fuel injector problem will cause a misfire condition.

The cool thing is the fuel injectors are very accessible on the 1.8L Mazda Protegé. And since they're accessible, they are pretty easy to test.

In this tutorial I'm going to show you how to test them by doing a multimeter resistance test. I'm also going to show you how I troubleshoot a bad or clogged fuel injector.

Contents of this article at a quick glance:

  1. Symptoms of Bad Fuel Injector.
  2. Checking the Injector's Internal Resistance.
  3. How to Find the BAD or Clogged Fuel Injector.
  4. Where to Buy the Fuel Injector and Save.

Symptoms of Bad Fuel Injector

When a fuel injector fails, it's usually due to its internal coil shorting out. This type of failure results in the fuel injector not spraying any fuel. The end result is a ‘dead’ cylinder.

Another common problem is the fuel injector becomes clogged. This results in the fuel injector not being able spray (atomize) fuel in a correct conical pattern.

Here are the most common symptoms you'll see when a one fails:

  1. Rough idle.
  2. Lack of power.
  3. Hesitation when you accelerate your Mazda Protegé down the road.
  4. Misfire trouble codes:
    1. P0300: Random Cylinder Misfire.
    2. P0301: Cylinder #1 Misfire.
    3. P0302: Cylinder #2 Misfire.
    4. P0303: Cylinder #3 Misfire.
    5. P0304: Cylinder #4 Misfire.

The test I'm gonna' show you deals primarily with shorted fuel injector coil windings. But, I'll also offer you a specific diagnostic strategy to find a clogged fuel injector (in the next page, heading: How to Find the BAD or Clogged Fuel Injector)

Checking the Injector's Internal Resistance

Checking the Injector's Internal Resistance With a Multimeter. How to Test a BAD Fuel Injector (1999, 2000 1.8L Mazda Protegé)

What we're going to do is check the internal resistance of all 4 fuel injectors. The internal resistance of each one should be between 12 to 16 Ohms ().

For this test you will need a multimeter that can measure resistance. If you don't have one check out my recommendation here: Buying a Digital Multimeter for Automotive Diagnostic Testing (at: easyautodiagnostics.com).

NOTE: Your fuel injector resistance test should be done with your Mazda's engine cold. If the engine has been running for any extended length of time, let it cool down completely.

These are the test steps:

  1. 1

    Disconnect the fuel injectors from their engine wiring harness connectors.

    NOTE: To identify which cylinder the fuel injector belongs to, see the above illustration with the cylinder # for the 1.8L Mazda Protegé.

  2. 2

    Set your multimeter to Ohms (Ω) mode and:

    Measure the resistance of the fuel injector across its two male spade terminals with the multimeter test leads (see the illustration in the image viewer).

  3. 3

    Write down the resistance value that your multimeter records for the specific fuel injector you're testing. The illustration above will help you identify the cylinder # the fuel injector belongs to.

  4. 4

    Repeat steps 1 through 3 on the remaining fuel injectors.

    NOTE: The fuel injector resistance specification is: 12 to 16 Ohms.

Let's find out what your specific multimeter test results mean:

CASE 1: The resistance of all four fuel injectors is between 12 - 16 Ohms. This is the expected and correct test result and tells you that none are shorted or open internally.

If you suspect that you have a clogged fuel injector, which a resistance test won't find, take a look at the following section: How to Find the BAD or Clogged Fuel Injector.

CASE 2: One of the fuel injectors registered a resistance value not within the specification. This test result tells you that this particular fuel injector is bad. Replace the fuel injector.