RING-PISTON 7N7078 - Caterpillar

The ECM automatically compensates for engine operation at higher elevations. The ECM derates the fuel delivery according to the barometric pressure. The barometric pressure is sensed by the atmospheric pressure sensor. The atmospheric pressure has an effect on the performance of the engine. Derating the fuel delivery maintains the temperatures of the exhaust gas within acceptable limits.The derating of the engine starts at a specific barometric pressure. The barometric pressure is equal to the atmospheric pressure of an elevation. The atmospheric pressure is specific for the engine and for the engine rating. The default settings that are programmed at the factory are listed in Table 1.
Table 1
Altitude    
Parameter     Default Setting    
Derate setpoint     2T specification    
Security level     Required password    
Derating per
305 m (1000 ft)     3%    
Maximum derating     35% of the rated power    If the barometric pressure is below the setpoint, a warning and a derating will occur. The continuous schedule of the derating is three percent per 1 kPa (.15 psi) of pressure below the setpoint. The maximum derating is 35 percent.Input For The Atmospheric Pressure Circuit
Atmospheric pressure is monitored by the atmospheric pressure sensor. The sensor is located on the mounting for the ECM. A 5.0 0.5 VDC supply voltage is provided by the ECM. The output of the atmospheric pressure sensor is a DC signal. The sensor's output voltage is 0.2 volts to 4.8 volts. The ECM interprets the output voltage as atmospheric pressure.