Catalytic Converter/Muffler

TM 9-2320-312-24-2

Testing and Adjusting Section

Catalytic Converter/Muffler

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Illustration 55

(A) Catalytic converter/muffler

(B) 152 mm (6 inches)

(D) Turbocharger or exhaust manifold

(1) Preferred test location

(2) Optional test location

The location of the back pressure tap is important

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Illustration 56

in order to obtain an accurate back pressure

Typical example

reading. The test location should be located on a

straight length of exhaust pipe. This back pressure

(1)

Catalytic converter/muffler

(2)

Test location

tap should be located as close as possible to the

(3)

Exhaust piping

turbocharger or the exhaust manifold. The tap

(4)

Turbocharger

should be located at least 305 mm (12 inches)

downstream of a bend. The tap should have

1. Connect the pressure port of the differential

152 mm (6 inches) before a bend. If a continuous

pressure gauge to the test location. The test

straight length of exhaust that is 457 mm (18 inches)

location should be located on a straight length of

is not available, the tap should be located as close

exhaust pipe. This back pressure tap should be

as possible to the neutral axis on an elbow.

located as close as possible to the turbocharger

or the exhaust manifold.

If the exhaust is not equipped with a back pressure

tap, the following procedure may be used in order

2. Leave the vacuum port of the differential pressure

to install a pressure tap.

gauge open to the atmosphere.

1. Mark the position for the pressure tap.

3. Start the engine. Run the engine in the no-load

condition at high idle until the engine reaches

2. Weld or braze a 1/8 inch NPT half coupling to

normal operating temperature.

the exhaust pipe.

4. Record the value.

3. Drill a 3.18 mm (0.125 inch) hole through the wall

of the exhaust inside the half coupling.

5. Multiply the value from Step 4 by 1.8.

4. Remove any burrs from the inside of the exhaust

6. Compare the result from Step 5 to the value that

pipe.

follows.

Use the differential pressure gauge of the 1U-5470

Maximum back pressure for engines without a

Engine Pressure Group in order to measure back

catalytic converter/muffler .......................... 10.0 kPa

pressure from the exhaust. Use the following

(40 inch of H2O)

procedure in order to measure back pressure from

the exhaust:

Maximum back pressure for catalytic

converter/muffler .............. 14.9 kPa (60 inch of H2O)

If the maximum back pressure is within the allowable

limits, refer to Troubleshooting, "Low/Power/Poor or

No Response to Throttle".