my car hestitate around 3500-4000 rpm then backfires...the tach and radios goes on and off when i turn the headlights on....why does it backfires so much? and why do my tach and radio dont work well when my light s are on?

 

Bad engine grounds are the likely culrpit, along with perhaps a faulty alternator.

 

prolly a week alternatr, and most rx7's backfire alot, when you let off the gas