I'm trying to figure out my 1982 Berlinetta. It's a 2BBL 2.8L V6, and the check engine light is on. When I ground the diag port, I get nothing. Not even a code 12. I've tried resetting the computer by disconnecting the memory circuit, then disconnecting the battery, neither of which turned off the light. The car runs a little rich, but other than that runs and idles fine. Maybe it's a faulty ECM? I've quadruple-checked for loose wires or hoses.