how to troubleshoot a misfire in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.
• Allow the engine to cool before beginning any repairs.

2. Inspect and Replace Spark Plugs

• Tools Required: Socket set, torque wrench, spark plug socket
• Remove the engine cover if applicable.
• Disconnect the ignition coil connectors and remove the ignition coils.
• Using a spark plug socket, remove the spark plugs.
• Inspect the spark plugs for wear or damage; replace if necessary.
• Torque the new spark plugs to the manufacturer’s specifications (typically around 13-20 lb-ft).
• Reinstall the ignition coils and connectors, ensuring a secure fit.

3. Check and Replace Ignition Coils

• Tools Required: Socket set, torque wrench
• If the misfire persists after replacing spark plugs, inspect the ignition coils.
• Remove the coils from the spark plugs.
• Test each coil with a multimeter according to the manufacturer’s specifications.
• Replace any faulty coils with new ones and torque to manufacturer's specifications.

4. Fuel System Inspection

• Tools Required: Fuel pressure gauge
• Connect the fuel pressure gauge to the fuel rail.
• Turn the ignition to the "On" position (do not start the engine) and check the fuel pressure.
• Compare the reading to manufacturer specifications (typically around 50-60 psi).
• If pressure is low, check the fuel filter and fuel pump. Replace as necessary.

5. Checking for Vacuum Leaks

• Tools Required: Smoke machine or carburetor cleaner
• Use a smoke machine to check for vacuum leaks around intake manifold gaskets, vacuum hoses, and throttle body.
• Alternatively, spray carburetor cleaner around suspected areas while the engine is running; an increase in RPM indicates a leak.
• Replace any damaged hoses or gaskets.