[jibe]

The part of your post that made me curious was whether fuel mapping, or ECU swapping was illegal. It looks like it is in a grey area under Clean Air Act, but generally interpreted as legal as long as you aren't doing things to make your emissions worse.

[tpmoney]

At least as far as ECUs go, almost every after market ECU I’ve seen doesn’t control OBD II or the CEL (or does so very minimally) and is therefore immediately in violation of not conforming to the requirements to retain OEM level behavior. Fuel mapping is more grey, largely due to the ability of some OEM ECUs to be reflashed and thus retain OBD behavior.