How To Test The Fuel Injectors (Toyota 1.8L)

How To Test The Fuel Injectors (Toyota 1.8L)

Having a fuel injector go bad doesn't happen every day but it does happen. When one does go bad, it'll cause your Toyota's engine to misfire and it'll idle rough.

Testing the fuel injectors on your 1.8L Toyota isn't hard. In this tutorial I'm gonna' show you a very specific way of testing them that'll help you nail down the bad fuel injector.

In Spanish You can find this tutorial in Spanish here: Cómo Probar Los Inyectores De Combustible (1.8L Toyota Corolla) (at:

Symptoms Of A Bad Fuel Injector

Each of your Toyota's 1.8L engine's cylinders needs fuel, air (compression) and spark for the combustion process to occur and keep your car running happily down the road.

So, when one of the fuel injectors stops injecting fuel, the cylinder that fuel injector belongs to will go ‘dead‘. A ‘dead’ cylinder will cause a misfire and you'll see one or more of the following:

  • Engine will have a rough idle.
  • Engine will misfire under load, especially when you accelerate your Toyota.
  • Lack of power when accelerating your Toyota.
  • Bad gas mileage.
  • Since your 1.8L Toyota vehicle is OBD II equipped, you'll usually see a misfire code (P0300, P0301, P0302, P0303, P0304) lighting up the check engine light on your instrument cluster.

So, what causes a fuel injector to go bad? It's usually just old age, although not always. Which leads up to the 3 main types fuel injector failure:

  1. Fuel injector doesn't spray any fuel because it has fried internally.
  2. Fuel injector sprays fuel, but not enough (clogged fuel injector).
  3. Fuel injector stuck on all of the time (as soon as the key is turned ON). This is usually, but not always due to a bad fuel injection computer.

This article focuses on the most common, which is when the fuel injector doesn't spray any fuel at all due to an internal short circuit.

What Tools Do I Need To Test The Fuel Injectors?

To test the fuel injectors in your 1.8L Toyota you don't need any expensive tools.

Here's a basic list of tools you'll need to test all four fuel injectors:

  1. A multimeter.
  2. Scan tool.
    • To actually test the fuel injectors, you don't need a scan tool (since a scan tool can't dynamically test the fuel injectors). But, having one makes the whole process easier since you're able to retrieve any diagnostic trouble codes (DTCs) stored in the PCM memory.
    • Don't have one? Check out my recommendation: Abe's Scan Tool Recommendation.
  3. Pen and paper to write down your fuel injector resistance test results.

TEST 1: Identifying The ‘Dead’ Cylinder

How To Test The Fuel Injectors (Toyota 1.8L)

The very first thing you need to do is find the cylinder that's misfiring.

There are two ways to find the misfiring cylinder. One is by reading the diagnostic trouble codes and seeing if you have a specific misfire code.

The other is doing a simple manual cylinder balance test and in this test step I'll show you how to do one.

Once this ‘dead’ cylinder is found, the next step is to do a resistance test of all four fuel injectors.

Alright, here's how to do a manual cylinder balance test:

  1. 1

    Start the engine and let it idle. Let it idle for at least 3 to 5 minutes before you start the next step.

  2. 2

    Unplug the #1 fuel injector's connector and see if it has a negative effect on the engine's idle.

    By negative effect, I mean that the engine's idle gets rougher/worse.

  3. 3

    Re-connect the fuel injector and repeat the test on this same fuel injector.

    You can repeat this (unplugging and re-plugging the fuel injector's connector) as many times as you need to make sure of your test results.

  4. 4

    Repeat steps 2 thru' 3 on the other 3 fuel injectors.

    Remember, what you're after is to see if unplugging the fuel injector's connector has NO effect on the engine's idle since this will confirm that this cylinder is ‘dead’ and the one causing the misfire.

Let's take a look at your test results:

CASE 1: Unplugging the fuel injector's connector HAD NO effect on the engine's idle. This test result tells you that that specific cylinder is ‘dead’ and the cause of the misfire.

The next step is to test the resistance of the fuel injectors. For this step, go to: Testing The Fuel Injector's Resistance.

CASE 2: Unplugging the fuel injector's connector had an effect on the engine's idle (all 4 fuel injectors). This test result tells you that the misfire is either intermittent (not present at this time) or that the problem (causing the rough idle) is affecting all 4 cylinders evenly.

This test result also rules out your Toyota having a bad fuel injector.

Chevrolet Vehicles:

  • Prizm 1.8L
    • 1998, 1999, 2000, 2001, 2002

Pontiac Vehicles:

  • Vibe 1.8L
    • 2003, 2004, 2005, 2006, 2007, 2008

Toyota Vehicles:

  • Celica 1.8L
    • 2000, 2001, 2002, 2003, 2004, 2005

Toyota Vehicles:

  • Corolla 1.8L
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
  • Matrix 1.8L
    • 2003, 2004, 2005, 2006, 2007, 2008
  • MR2 Spyder 1.8L
    • 2000, 2001, 2002, 2003, 2004, 2005