1990 tach drops while in boost and CEL please help video inside

[jaycemocapaldi]

I recently went back to a 1990 ecu after rewiring the pinout for a 1991+. After wiring the pinout back to the 1990 and installing the 90' tach, the needle still drops under boost. I am also having a issue when i very first put my foot on the pedal it will hessitate and almost die then jumps back up and drives fine. when in second its a little hoppy, but just feels like small bumps in the road. any ideas? i really need the help its my DD.

October 16, 2011 3:54 PM - YouTube

there is a short video

 

[GofaST4life]

Wow.

To me it almost looked like the needle was working in a reverse manner.

Have you tried installing the 1991 ECU to see if the problem is still there?

 

[jaycemocapaldi]

it wont drive with a 1991+ ECU, without rewiring the pinout. it will run but not drive the car will die. When i had the pinout reversed, the tach still dropped. The needle only drops under boost as if it was hooked up for a 1991+ ECU. I know it is a 1990 ECU because i had to rewire it back to work again.