How can I test for reason to misfires?

Question

Yesterday I changed my spark plugs and wires and now it's still misfires and has codes P0446, P1381, and P0300 I need help to get to what's wrong with my truck please

Answer 1

Did you have a misfire before replacing the spark plugs and wires? the P1381 and P0300 mean that the engine is misfiring but does not specify which cylinder is misfiring. The P0446 code is for the EVAP system.

You could try disconnecting one plug at a time, and check if the engine changes the RPMs when the plug is disconnected.

P0300 GMC - Cylinder Misfire Detected Random Cylinders
Read more: https://www.autocodes.com/p0300_gmc.html

P1381 GMC - Misfire Detected - No Communication with Brake Control Module
Read more: https://www.autocodes.com/p1381_gmc.html

P0446 GMC - Evaporative Emission Vent System Performance
Read more: https://www.autocodes.com/p0446_gmc.html