I have a very similar problem with my '89 B2600i. I have learned it is not an unusual problem. If you haven't already done so, check the MAZDAWORLD.org forum; specifically the B Series truck subforum. There is some info regarding our problem and a fellow who goes by the username TRYNITAR who seems to really know his stuff posts a lot of answers. Good luck. If you get anything useful, please post it here, too. Thanks