Fuel or air.
The most likely cause of low-power, when under load, in your Cummins N14 diesel engine is a lack of fuel. The problem can also be a lack of air flow.
Most likely a 5.9 liter cummins turbo diesel 12v
Really depends on the type. A Type A school bus might have a gas, diesel, or CNG engine.. those will use whatever is standard for the chassis manufacturer (e.g., Triton gas or Powerstroke diesel for Ford chassis, Vortec gas or Duramax diesel for General Motors chassis, Hemi gas or Cummins diesel for Dodge chassis). For Type B, C, and D buses, Thomas Built buses is owned by Daimler A.G. - the parent company of Freightliner, Western Star, and Mercedes Benz, and have been available with Cummins, Mercedes-Benz, or Caterpillar (until 2009) diesel engines or Cummins CNG engines. IC Bus is a subsidiary of Navistar International, and can have Navistar MaxxForce or Cummins diesel engines, or Cummins CNG engines. Blue Bird does not make their own engines, so they will use Cummins diesel or CNG engines. In the case of diesels, 6 - 7 liters is most likely what you'll find, though I have, in the past, seen school buses with 7.3 liter 3126 and C7 Caterpillars.
Either it will not run at all, or run very poorly. Either is likely to do severe damage to the engine.
Diesel
It does not have any sort of fuel type sensor, putting gasoline into the fuel tank of a diesel Mercedes will likely destroy the engine.
A very likely cause is a failed radiator fan.A very likely cause is a failed radiator fan.
Depends. An older Diesel is likely to keep running. A modern, with a full set of electronic engine diagnostic might not.
Most likely the problem is with the Pressure Sensor in the engine block.
They run on the water. They most likely use diesel fuel to power the engine.
More than likely no damage was done. Drain out all the oil and fill it with the correct weight diesel oil.
Injectors and fuel system would likely be ruined, it'll smoke heavily, acceleration would be greatly affected. A very costly mistake.