how to diagnose a misfire on Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is off.
• Disconnect the battery to prevent electrical shocks.

2. Replace Spark Plugs

1. Remove the engine cover if applicable.
2. Using a socket wrench, carefully remove each spark plug.
3. Inspect the spark plugs for wear; if they are fouled or worn, replace them with OEM-spec plugs.
4. Apply anti-seize lubricant to the threads of the new spark plugs.
5. Torque the new spark plugs to the manufacturer's specifications (typically around 13-16 lb-ft).

3. Inspect and Replace Ignition Coils

1. Disconnect the wiring harness from the ignition coils.
2. Remove the bolts securing the ignition coils and extract the coils.
3. Visually inspect the coils for cracks or signs of wear.
4. Test the resistance with a multimeter; replace any faulty coils with new ones.
5. Reinstall the ignition coils and reconnect the wiring harness.

4. Fuel System Inspection

1. Connect a fuel pressure gauge to the fuel rail.
2. Turn the ignition to the "ON" position (do not start) to check fuel pressure.
3. Compare the reading to the manufacturer’s specification; it should typically be around 50-60 psi.
4. If the pressure is low, inspect the fuel pump and filter for blockages or failures.

5. Vacuum Leak Check

1. Start the engine and listen for hissing sounds that indicate vacuum leaks.
2. Use a smoke machine or carburetor cleaner to detect leaks around the intake manifold and hoses.
3. Repair or replace any damaged hoses or gaskets.

6. Compression Test

1. Remove the spark plugs to facilitate compression testing.
2. Insert a compression gauge into each cylinder and crank the engine.
3. Record the compression readings and compare them to specifications (typically around 150-200 psi).
4. If readings are low, inspect for valve or head gasket issues.