[slownugly]

Yea the vx tran is very low. I'm at 2k at about 65mph. It's becoming a popular swap with hxs. I believe it requires some driving style changes so a scan gauge would help a lot. I think it allows more flexibility with lean burn because guys were having trouble keeping their hxs in lean burn. I've never driven an hx so do some searching around. One build In particular was returning 60+ mpg.

Yea the 420 is a cat code. I've never seen an o2 cause a cat code. If an O2 is staying lean or rich it would throw a code specific to that. If you've ever seen data pids for oxygen sensors the front sensor normally switches between .2-.8 volts. The rear o2 looks for a change in voltage which indicates a chemical reaction and the converter is working properly. If both voltages are identical or almost identical it will throw a cat code because the ecu senses that the cat is no longer performing a chemical reaction. Check for exhaust leaks too. That may have the capability of throwin the code.

Our wideband o2s do not operate in the normal .2-.8 range but the cat monitoring is the same principle. I have 1 cat attached to one of my engines but I'm pretty sure it won't fit the hx.

Edit: plus the chemical composition of it is pre obd2 so it would likely throw a code even if it fit.