Plugged in OBDII. Got codes for misfiring on cylinders 1,2, and 3 as well as a random misfire code. Also bank 1 oxygen sensor code and P0420 catalyst below efficiency (I've had that last code for awhile and the code comes and goes). What is causing the misfires?
My car has 270000 miles.
My car has an automatic transmission.
Misfires can be caused by several things. I would first check for vacuum leaks, then I would pull the plugs to see if they need replacing. It is possible that have a fuel system concern, but I would lean more towards a vacuum leak. The amount of air the engine intakes, is measured to ensure that the proper amount of fuel is delivered. If there is a vacuum leak, extra air that the engine is not expecting enters and causes the air/fuel mixture to be wrong causing a misfire. If you need help pinpointing the problem, a certified technician, like one from YourMechanic, will be able to diagnose the misfiring issue and help you move forward with repairs.