Group 25 Intake and Exhaust System System Check
Exhaust Backpressure, Checking
Pressure gauge: Of indicating or U-tube type, graded to
24 kPa or 2,440 mm water column (3.5 psi) and
equipped with damper.
Steel pipe: About 200 mm (8 in.) long and able to con-
nect to a union.
Union: The union must be brazed onto the exhaust pipe
as shown. Then drill a 1.5 – 2.0 mm (0.06 – 0.08 in)
hole through the center of the union and the side of the
exhaust pipe.
Hose: The hose is installed between the pressure gauge
and steel pipe and must be long enough for the gauge to
be read inside the cab.
T2006988
Measuring equipment
1 Damper
2 Pressure gauge
3 Steel pipe
4 Union
Pressure Testing Outlet Location
The pressure-testing fitting should be located on as
straight a section of the pipe as possible, two-thirds after
and one-third before a bend in the pipe.
The test fitting must not be located on an outer or inner
bend of the exhaust pipe.
T2006983
Outlet location
Backpressure Measuring Techniques
Using a chassis dynamometer is the best way to mea-
sure backpressure. If such equipment is not available,
the vehicle can be driven up a long hill. The accelerator
pedal must be kept fully floored with the vehicle acceler-
ating up the hill until the engine reaches specified rpm.
Note the highest backpressure reading and compare it
with specifications.
After the test, make sure to block off the union in the ex-
haust pipe with a plug, or in some other suitable manner.
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