This is actually for my boat, not my car, but I would think its the same thing (4 stroke engine).

The voltage at the battery is only reading 13.4V at 2500rpm. I have always seen 14.6 volts minimum. Could a bad battery (it would have to be two batteries in this case) cause this, or would it have to be an alternator/regulator problem.

John

Unique 289FIA #9367
351W Fuel Injected