would a pm9 ecu work in place of the pm6 ecu in the 88-91 civic hb si, i bought the ecu from a salvage yard and said it woudl work, hooked it up, engine stutters, does anyone know? pm would help

 

its not made for your car....

obviously.

 

It's the same ECU as your PM6, but with minor differences for the particular engine it is tuned to run. The PM5/6/7/8/9 are all the same family, and same circuit board, etc. with a handful of parts differences and different programs.
Stick with the PM6.