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.
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