why does my GMC Sierra T1XX (2019-Present) experience engine misfires?

Learn how to diagnose and fix P0300 engine misfire in GMC Sierra T1XX. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather necessary tools and parts. Ensure the vehicle is on a flat surface and the engine is cool.
• Tools Required: OBD-II scanner, socket set, torque wrench, feeler gauge, multimeter, fuel pressure gauge.

2. Replace Spark Plugs

1. Disconnect the negative battery terminal to prevent electrical shorts.
2. Remove the ignition coil(s) by unscrewing the retaining bolts and gently pulling them off the spark plugs.
3. Use a socket wrench to remove the worn spark plugs.
4. Check the gap of the new spark plugs with a feeler gauge and adjust to manufacturer specifications (usually around 0.040 inches for most GM engines).
5. Install the new spark plugs, tightening to the manufacturer-recommended torque (typically 11-15 lb-ft).
6. Reattach the ignition coils.

3. Inspect and Replace Ignition Coils (if necessary)

1. Use a multimeter to test the resistance of each ignition coil.
2. If readings are outside the specified range, remove the faulty coil.
3. Install the new ignition coil, ensuring proper alignment and seating.

4. Check and Clean Fuel Injectors

1. Attach a fuel pressure gauge to the fuel rail to check for proper fuel pressure (refer to manufacturer specifications).
2. If pressure is low, inspect the fuel filter and fuel pump for issues.
3. Clean the fuel injectors using a fuel injector cleaner kit, or replace them if they are clogged or malfunctioning.

5. Inspect for Vacuum Leaks

1. With the engine running, visually inspect for any cracked or disconnected vacuum hoses.
2. Use a smoke machine or carburetor cleaner to detect leaks around the intake manifold.
3. Repair or replace any damaged hoses or gaskets.