Recently put in a JLP/Patriot headed engine in my truck (which is a story in itself). It idles fine and runs fine except when it gets under boost. It really stumbles, misses and blows black smoke. I'm pretty sure at least one cat is bad (rattles) as the result of a lean condition by the previous owner when he blew the motor. It read a code of 0171 lean condition bank one, but I think it may be more to it. Perhaps a bad MAF? I'm gutting the cats later this week but other than that any suggestions?

Thanks
EB

 

what you describe is a seriously rich condition.

 

Get a full diagnostic done by good tuner unless you have some sound knowledge yourself.

I had issues with rich on one bank
Turned out to a faulty injector flooding out one cylinder...