How to Test a BAD Fuel Injector (1999-2001 2.0L Mazda Protegé)

One of the hardest working components on your 1.6L Mazda Protegé is the fuel injector. Your Mazda Protegé is equipped with four of them. Sooner or later one of them is going to fail. When it happens, the most obvious symptom you're going to get is a misfire condition (rough idle condition).

The cool thing is that you don't need any expensive testing equipment to find out if you have a bad fuel injector or not. This also means that you can test them yourself since all you'll be doing are simple multimeter resistance tests. In this tutorial I will show you how to do them in a step by step way.

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

Fuel injectors usually fail in one of two ways. Either the fuel injector shorts internally and quits injecting fuel, or the injector gets clogged and doesn't inject enough fuel. Whether the injector gets clogged or stops completely, I can tell you that it usually causes your engine to misfire or to idle rough.

Having the fuel injector's internal coil winding short out is one of the most common type of fuel injector failures. The other is a clogged fuel injector that can no longer spray (atomize) fuel in a correct conical pattern.

Since a fuel injector injects the fuel the cylinder needs to produce power, when one fails (or gets clogged) it'll have serious repercussions in engine performance. 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 (1999-2001 2.0L Mazda Protegé)

The most common way to find out if any of the four fuel injectors are bad, is to check there internal coil winding. Specifically we are going to use our multimeter in ohms mode to see if the coil winding is shorted or open. Once we get our multimeter resistance value, we are going to compare this value to the specification from Mazda.

The factory fuel injector resistance for the 1999-2001 2.0L Mazda Protegé is 13.8 Ohms ().

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 ID number for the 1.6L 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: 13.8 Ohms.

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

CASE 1: Your test results confirm that all fuel injectors' resistances are within specification. 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 indicates that the fuel injector is BAD. Replace the fuel injector.