Wondering if a fuel injector is bad? I'll walk you through a quick multimeter resistance test. This simple check lets you figure out if there's an internal electrical issue with the injector.
On top of that, I'm gonna give you a step-by-step diagnostic guide. If you're not sure where to begin, this guide will help you track down the faulty or clogged injector.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 1.6L (4A-FE) Toyota Corolla: 1989, 1990, 1991, 1992.
- 1.6L (4A-FE) Geo Prizm: 1989, 1990, 1991, 1992.
Fuel Injector Circuit Wiring Diagrams:
- Fuel Injector Circuit Wiring Diagram (1989 1.6L Toyota Corolla).
- Fuel Injector Circuit Wiring Diagram (1990-1992 1.6L Toyota Corolla).
Symptoms Of A Bad Fuel Injector
Fuel injectors usually fail in two main ways:
- Clogged injector: It still sprays fuel, but it doesn't atomize it properly, which messes with the cylinder's ability to combust the air/fuel mixture.
- Burnt-out injector: No fuel gets sprayed at all, so that cylinder won't fire.
As you're already aware, each cylinder in your Toyota's 1.6L engine needs fuel, air, and spark to make power. So, if the injectors quit spraying, you're definitely gonna deal with a misfire.
Here are a few signs you might notice:
- Rough idle: The engine runs unevenly when stopped, shaking more than usual and feeling unstable.
- Loss of power: You press the gas, but the car feels sluggish and struggles to pick up speed.
- Hesitation: When you speed up, the engine stumbles or hesitates before responding, making acceleration feel jerky.
This tutorial focuses on testing if the injector's internal coil has failed, making it stop injecting fuel. But checking for a clogged injector isn't much harder —I'll walk you through that in this tutorial.
Checking The Injector's Internal Resistance
Testing the fuel injectors on the 1.6L engine is pretty straightforward since they're easy to reach. We're gonna check each injector's internal resistance and compare it to the factory specs.
If an injector's burnt out, its resistance won't match the spec, and you'll notice its reading is way off compared to the others.
The steps below assume you're testing all four fuel injectors.
- 1
Unplug each fuel injector from its connector.
NOTE: Check the illustration above to match each injector to its cylinder number on the 1.6L Toyota engine. - 2
Turn your multimeter to Ohms (Ω) mode.
- 3
Use the multimeter leads to measure the resistance across the injector's two male spade terminals (refer to the image viewer for guidance).
NOTE: The expected resistance for a 1.6L Toyota injector is between 13.4 and 14.2 Ohms. - 4
Record the resistance reading for the injector you're testing.
The illustration above will help you match the injector to its cylinder number. - 5
Repeat steps 1 through 4 for the remaining injectors.
Let's break down what your multimeter test results mean:
CASE 1: All four injectors have resistance values within spec (or close to each other). That means the fuel injectors are working fine —none are shorted or internally open.
Why? If an injector had an internal short or open-circuit, its resistance would've been way off compared to the others. Since all four readings are consistent, you can rule out injector failure.
CASE 2: One injector's resistance is totally different from the rest. That's a clear sign the injector's bad. You'll need to replace it.
How To Find The Bad Or Clogged Fuel Injector
Figuring out whether a clogged or bad fuel injector is causing the misfire (rough idle, engine miss) on your 1.6L Toyota Corolla (or 1.6L Geo Prizm) is actually a pretty straightforward process.
The diagnostic guide below has nailed down failed or clogged fuel injectors about 95% of the time, saving time, money, and frustration. Following these troubleshooting steps should help you too!
Alright, here's the exact process I use when diagnosing a bad fuel injector:
- Pinpoint the 'dead' cylinder first.
- Do a cylinder balance test to find which cylinder isn't firing properly.
- This tutorial will help you with this test:
- Check that all spark plug wires are delivering spark.
- Use a dedicated spark tester to confirm each cylinder is getting spark.
- Make sure the spark plug boot and spark plug aren't soaked in engine oil.
- Pull out the spark plugs and inspect them for cracks or carbon tracking (this is a crucial step).
- Carbon tracks can cause misfires—here's a real-world case study:
- Carbon Tracks Are A Common Cause Of Ignition Misfires (via easyautodiagnostics.com).
- This tutorial will help you check the distributor cap and spark plug wires:
- Test engine compression.
- Once you're sure all four cylinders are getting spark, check for low engine compression.
- Compression tests are often overlooked when diagnosing misfires or rough idle issues.
- Here's how to run the test:
- Perform a Noid light test.
- If everything else checks out, the next step is using a Noid light to test the fuel injector.
- This test helps confirm whether the injector is actually getting activated.
- Need more details? Check out this guide:
- How To Use A Noid Light And Where To Buy It (via easyautodiagnostics.com—not the most in-depth article, but it'll give you a solid idea).
- Swap the suspected bad injector with a neighboring one.
- If you've confirmed a specific cylinder isn't firing and:
- The ignition system isn't the issue,
- The cylinder's compression is good,
- The fuel injector's resistance checks out, and...
- You suspect the injector might be clogged, swap it with the one next to it.
- If the misfire follows the injector to the new cylinder, you've found the problem —the injector is clogged or bad and needs cleaning or replacement.
- If you've confirmed a specific cylinder isn't firing and:
Tracking down a bad or clogged fuel injector on your 1.6L Toyota Corolla (or 1.6L Geo Prizm) can be tricky, but it's totally doable. The key is identifying the 'dead' cylinder first. This step-by-step strategy has saved me plenty of headaches, and I bet it'll help you too!
More 1.6L Toyota Corolla Tutorials
There are several more ‘how to’ tutorials that I've written that are 1.6L Toyota Corolla specific, that may be of further help. You can find them here:
Here's a small sample of the tutorials you'll find in the index:
- How To Diagnose A Broken Timing Belt (1989-1997 1.6L Toyota Corolla).
- How To Test The Ignition Coil (1989-1992 1.6L Toyota Corolla).
- How To Test The Fuel Pump (1989-1992 1.6L Toyota Corolla).
- How To Test Engine Compression (1989-1997 1.6L Toyota Corolla).
If this info saved the day, buy me a beer!
