96 355 dropping a bank of cylinders.

The right CAT ecu and the bypass ecu are mounted next to each other. The wire harness plugs for both are the same design. Mine were switched. So, the main engine ecu was getting the reading from the cat thermocouple and thinking that was the voltage of the bypass. Bypass and cat operate at different temp thresholds. I was just getting a flashing SDL.

Looking back, I think I had two problems, first, one ecu was bad, and second, the plugs were swapped. I hope I have it solved. I haven't had time to street test it yet. No pending codes and no flashing sdl.

As I have learned from others, you really need to understand how the system works, in order to flow chart diagnostics to figure out which part is bad. Seems simple to me now, but it took a lot of reading and a few fchatters to beat it into my thick head!

I hope that makes sense.