how to diagnose a misfire in my Ram 1500 DT (2019-Present) with code P0300?

Solution

1. Preparation

• Gather tools and parts.
• Disconnect the battery to avoid electrical shocks.
• Allow the engine to cool before starting work.

2. Replace Spark Plugs

1. Remove the engine cover if necessary.
2. Use a socket set to remove the spark plug wires or ignition coils.
3. Using a spark plug socket, carefully unscrew and remove the old spark plugs.
4. Check the gap of the new spark plugs and adjust to manufacturer specifications.
5. Install the new spark plugs by hand to avoid cross-threading, then tighten to the specified torque (usually around 13-15 ft-lbs).
6. Reattach the ignition coils or spark plug wires.

3. Inspect and Replace Ignition Coils (if necessary)

1. Disconnect the electrical connector from the ignition coil.
2. Remove the bolts securing the coil using a socket set.
3. Pull the ignition coil straight out and replace it with a new one.
4. Reconnect the electrical connector and ensure it clicks into place.

4. Fuel System Check

1. Attach a fuel pressure gauge to the fuel rail service port.
2. Turn the ignition to the ON position (do not start) and check the pressure reading against manufacturer specifications.
3. If pressure is low, inspect the fuel pump, filter, and lines for obstructions or failure. Replace parts as necessary.

5. Compression Test

1. Remove the spark plugs to allow for easier cranking.
2. Insert the compression gauge into the spark plug hole of the first cylinder.
3. Have an assistant crank the engine for 5-10 seconds while you read the gauge.
4. Record the compression readings for each cylinder; if any are significantly lower than others, further investigation is needed.