Running rough

My 99 burb is having problems starting. It will crank hard and back fire. When started, it is missing badly and pinging really bad. The only code is for miss firing. My O2 sensors are reading 2-3% on the front 2 and the back 2 are 99%.

My 99 burb is having problems starting. It will crank hard and back fire. When started, it is missing badly and pinging really bad. The only code is for miss firing. My O2 sensors are reading 2-3% on the front 2 and the back 2 are 99%.

`you can have alot of componets cause this type of problem . what have you done to inspect for defects. what are the service intervals for things like plugs fuel filter wires air filter condition of engine [oil burner] etc...mileage and some maintanence history. o2 readings on an engine that is miss firing are not helpfull.......