The way i read it (and please correct me if not right) is that the f16 doesnt have an APU as such,but a JFS..which is jet fuel starter.
When the pilot starts the engine it empties a hydraulic accumulator (3000psi) which spins a hydraulic motor.I thought this motor uses jet fuel and spins up to rapid speed which in turn spins the main engine via a gearbox and clutch.
The accumulator then refills and is used for another start or the wheel brakes
The f16 has an EPU (emergency power unit) and that uses hydrazine but i think that can only be used for 10 mins.I dont think this is used for the engine, just controls /landing gear etc......but like I said please correct if wrong.