High Altitude Operation; Engine Braking System, Optional - freightliner Cargo Manual

Engines
4. If the engine is not being used, shut it down by
turning the ignition key off.

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.
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
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.
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.