[tomj76]

I finally received a replacement and replaced the defective converter. To my surprise it was actually fairly easily removed. I could immediately see that the first catalytic converter cell had melted and disintegrated. The honey comb for the second cell (in the first chamber) was clogged with the debris from the first cell.

I put the new pipe in and measured the acceleration... it came up to 100 hp @ 6000 rpm.

Two lessons I learned in this adventure are:

(1) Diagnosing with backpressure measurements in the shop requires that you create realistic exhaust flow rates. The diagnostic guides that I read instructed to use idle & idle @ 2000 rpm for the test. However, idle and high RPM idle settings don't really create much airflow because the throttle isn't open very far. The engine needs to open to >50% to simulate the air flow seen in the conditions where horsepower is needed. Gunning the engine is a reasonable approximation because the throttle is wide open for enough time to get an indicative test.

(2) I don't know what caused the converter cell to breakdown & melt, but it was obviously very hot. My guess is that the faulty CVVT solenoid on the intake cam was contributing to a large amount of unburnt gasoline to reach the converter. The average MPG was lower since that failure occurred, although a clogged exhaust can be the cause of that symptom. I ran the car for a few months with that condition, which may have lead to the failed converter.