12v to injectors when charging

My 91 GMC 2500 with a TBI 350. When ever there is a charge on the system, either with alternator or if I disconect alternator and hook up a battery charger. I end up with 12v to the injectors and flood out the engine. I have changed a lot of things including the computer, alternator, and distributor. When alternator is disconnected and no charge on system it runs fine.
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