2003 Chrysler 300M Special
Engine Size : 3.5ltr
Question: PO 172 code engine misfires on at least 2 cylinders when I pull a hill and the engine is under load, but not every time I pull a hill. Engine not lacking power when it is running good check engine light keeps coming on. I have changed the O2 sensors and the issue keeps coming back. Changed timing belt around 2000 miles ago and have not been bothered till now again.
Answer: The scan code of P0172 is a rich condition code. The oxygen sensors are seeing a rich exhaust, so if replacing the sensors did not fix the problem, you are getting the code because engine is actually running rich. This would not usually cause the problems you are having. A lean code of say- P0171 would though. The engine misfire means the fuel in those cylinders is not being burned, so thus the possible cause of the rich code.
Most engine misfire caused under heavy load is an ignition problem. Check the spark plugs, plug wires and ignition coils. Two of them may be "Breaking Down" under load. If you have a lot of miles, may just be time for a major tune up. Try spraying the ignition components with a spray bottle of water when the engine is running. this will usually cause a bad plug or plug wire to spark through. You may be able to hear or see the spark arching.
