The reason your 2012 Acadia is leaving black sooty droppings could be due to the car being on full throttle. This means that gas is dumped into the engine at maximum levels, which inevitably some of it does not burn. The un-burned gas goes to your catalytic converter and is split out as black smoke. It could also be that your car air filter is extremely dirty or a badly done chip. You can get a mechanic to help you find the possible cause for this.