A Simple Fuel Injector Diagnostic Strategy
Finding the exact cause of your Toyota's misfire can sometimes be a challenge since so many things can cause a misfire condition when they fail.
I know, I've been there before, so in this section I want to share with you some of the experience and knowledge I've gained over the past 20 years working as an automotive diagnostic tech and tailored specifically to the Do-It-Yourself'er like you.
The cool thing is that there IS a logical step-by-step way of finding out if the fuel injector (or anything else) is the one causing your engine to miss (misfire, idle rough).
These are the steps I take:
- Find the ‘dead’ (misfiring) cylinder first.
- Unfortunately, the PCM doesn't always set a specific bad fuel injector code, but when a fuel injector does go bad, you WILL see a misfire code.
- A manual cylinder balance is a must first step.
- The next step is to check for spark and thus eliminate the ignition system as the source of the problem.
- I want to emphasize this to you: It's very important to eliminate the ignition system from the get-go.
- What I'm looking for here is to confirm that the spark plug is getting spark and I do this with a dedicated spark tester (like an HEI spark tester).
- This article will help you troubleshoot the ignition coils:
- Next, I remove the spark plugs and visually inspect them.
- What I'm checking for are for cracks and/or carbon tracks and/or oil filling up the spark plug well. The following two tutorials will further help you:
- Carbon Tracks Are A Common Cause Of Ignition Misfires (at: easyautodiagnostics.com).
- Diagnosing a Toyota Corolla Misfire Case Study (Toyota 1.8L).
- Toyota 1.8L engines have a bad habit of leaking engine oil onto the spark plugs and COP coil boot (from the valve cover) and this is a common cause of an engine miss (misfire, rough idle).
- What I'm checking for are for cracks and/or carbon tracks and/or oil filling up the spark plug well. The following two tutorials will further help you:
- If everything above checks out OK, I then do an engine compression.
- This is a fast and easy test but is so often overlooked.
- What I'm looking for is to see if any one cylinder is too worn out. If it's too worn out, it will always have 15% lower compression that the highest compression reading of the four.
- The following tutorial will help:
- Check fuel injector resistance.
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.
If this info saved the day, buy me a beer!
