You should be able to switch between ECU's with a toggle on the panel somewhere, right? Each ECU has its own MAP sensor, so that should isolate the sensor issue.
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65