Celicasrule

I recently took my 1990 Celica gt4 for a dyno tune which showed a strange repeated dip in the graph which appears to be electrical rather the mechaniacal. The mechanic said the turbo was ok but he could not check further because the dyno machine was OBD II and my car isn't. Does anyone have any info about this. i.e. where can I get OBD 1 tuning info etc. Cheers.