2000 Honda Civic Engine Detonation

Multiple issues have appeared with this car - none of them have been catastrophic, as the car has been completely reliable. They all appear to be ignition or fuel related. The only item I have not changed to this point is the MAP sensor.

I replace the spark plugs and distributor cap every 30,000 miles - the components appear melted at this milage. This was first noticed at 60,000. I have heavy engine detonation under part load and full throttle. Some days it sounds like the bottom of the engine will fall out.

I have replaced multiple O2 sensors as the OBD codes indicate I have a problem with my pre-cat sensor. When I look at the sensor readings with the vehicle running at idle, the O2 readings bounce up and down. When I look at the after-cat sensor readings, these are rock-steady.

My engine is mechanically sound when performing a cylinder pressure and leakdown check.

I have kept up with all maintenance - I am on my third timing belt. Oil changes and coolant changes have not revealed any suspicions with a blown head gasket. The car still gets 38 mpg, and starts every morning.