Need to graph the output to see how they track. Does the software allow graphing? Or at least watch the values to see if the post cat stays relatively stable compared to pre cat it's doing its job however the dme is programmed to monitor just how flat the curve is for the post cat and when it starts to track the pre cat it sets the low efficiency flag.

The adapter slows the transfer of the output gasses basically acts like a capacitor so it gives say a 30 second average reading vs instant and worked perfectly for me to squeeze another couple years out of a then 18 yr old cat. I had already found a set of cats but was about $500 I'd rather put towards new tires. I also figured out how to install universal cat replacing existing: I would build a frame out of wood and metal to hold both sides of the exhaust pipe with the cat before cutting out the old to replace with a new generic cat (they can be had for $100 or less)