I bought a 92 z28 with a 305...someone in the history of the car put a stage III hyperchip in it. the car backfires a lot. it also is definitely burning rich. it's completely stocker other than that chip. we adjusted the timing (set at 6 degrees tdc) and tested the egr valve. no check engine light. just a really annoying problem..i was wondering if it might be this fuel-dumping chip. anyone have any suggestions?

thanks