Engines 4. If the engine is not being used, shut it down by turning the ignition key off. exhaust system from the engine exhaust manifolds, cre- ating an increase in exhaust back pressure. During ve- hicle deceleration, the engine must turn against the back pressure and this creates a braking effect on the driving wheels. High Altitude Operation Cummins Engines lose horsepower when operated at high alti- tude because the air is too thin to burn as much fuel as at sea level. This loss is about 3 percent for each 1000 feet (300 m) altitude above sea level for a naturally as- pirated engine. Most turbocharged engines are rated for higher altitudes than naturally aspirated engines.
An engine will have smoky exhaust at high altitudes unless a lower gear is used. The engine will not demand full fuel from the fuel system unless the engine is altitude- compensated by the use of a turbocharger. Shift gears as needed to avoid excessive exhaust smoke. WARNING Using the engine brake as a primary braking system when the service brakes are operable is dangerous. This can cause long, unpredictable stopping dis- tances, possibly resulting in personal injury or property damage. The exhaust brake is not felt as a normal braking force as with the service brakes, but is more of a gradual de- celerating effect, as if the service brakes were lightly applied.
The exhaust brake is used to aid the engine and the service brakes in slowing the vehicle, reducing service brake wear. Engine Braking System, Optional PacBrake Exhaust Brake A PacBrake exhaust brake is available as optional equipment. An exhaust brake is an auxiliary braking system that attaches to the engine exhaust system. An exhaust brake makes the engine act as a compressor. The exhaust brake functions by partially closing off the 4.9