96 voyager rally 3.3L BCM problem

Taken the van in to the mechanic, he came back saying BCM is faulty. I have purchased a second hand BCM same part number, same model number, but took it out of a 3.0 liter engine. Installed second hand one, same issue, van only runs for 3 seconds. Could this be because its out of a 3.0 L engine? and is there a way to flash the BCM to work for a 3.3L? Could it be the after market alarm/starter which is installed causing the engine to kill?

1996 Voyager Rally
3.3L Engine
Power Locks
No power windows
Has air conditioning
After market alarm installed/starter

Any and all help would be great.

As long as it has the identicle part number it should work. I don't think the engine type matters. A reprogramming may be worth a try. I would lean more towards the aftermarket alarm. Contact the manufacturer for help or disconnect it. We are talking BCM and not PCM correct?