Q: Codes p0300, p0304

Hi there. As you already know, replacing components without diagnoses can be expensive and time consuming without resolution. A faulty fuel injector(s) is a possibility but, the P0304 (#4 cylinder misfire) may be affecting other cylinders causing the P0300 (random cylinder misfire) code to set. This would indicate, a compression test and cylinder leakage test is in order, especially with the check engine light not flashing. A valve train related misfire (cylinder head valve not sealing) could be overcome with increased engine rpm (revolutions per minutes). I recommend having your vehicle’s check engine light be diagnosed and repaired by a certified technician, such as one from YourMechanic.