3126 Truck Engine (Military) Caterpillar

Air Inlet Restriction

There will be a reduction in the performance of the engine if there is a restriction in the air inlet system or the exhaust system.

Illustration 1	g00293196
1U-5470 Engine Pressure Group

Refer to Special Instruction, SEHS8907, "Using the 1U-5470 Engine Pressure Group" for the instructions that are needed to use the 1U-5470 Engine Pressure Group. Refer to Operation Manual, NEHS0818, "Using the 198-4240 Pressure Indicator Tool Gp" for the instructions that are needed to use the 198-4240 Pressure Indicator Tool Gp.

1. Inspect the engine air cleaner inlet and ducting in order to ensure that the passageway is not blocked or collapsed.

2. Inspect the engine air cleaner element. Replace a dirty engine air cleaner element with a clean engine air cleaner element.

3. Check for dirt tracks on the clean side of the engine air cleaner element. If dirt tracks are observed, contaminants are flowing past the engine air cleaner element and/or the seal for the engine air cleaner element.
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   Hot engine components can cause injury from burns. Before performing maintenance on the engine, allow the engine and the components to cool.

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   Making contact with a running engine can cause burns from hot parts and can cause injury from rotating parts. When working on an engine that is running, avoid contact with hot parts and rotating parts.

4. Use the differential pressure gauge of the 1U-5470 Engine Pressure Group or the 198-4240 Pressure Indicator Tool Gp.
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   Illustration 2	g00678913
   (1) Turbocharger (2) Air Inlet Piping (3) Test location (4) Air cleaner

   1. Connect the vacuum port of the differential pressure gauge to test location (3). Test location (3) can be located anywhere along air inlet piping (2) after engine air cleaner (4) but before turbocharger (1).

   2. Leave the pressure port of the differential pressure gauge open to the atmosphere.

   3. Start the engine. Run the engine in the no-load condition at high idle.

   4. Record the value.

   5. Multiply the value from Step 4.d by 1.8.

   6. Compare the result from Step 4.e to the appropriate values that follow.

The air flow through a used engine air cleaner may have a restriction. The air flow through a plugged engine air cleaner will be restricted to some magnitude. In either case, the restriction must not be more than the following amount:

Maximum restriction ... 6.2 kPa (25 inch of H₂O)

The air flow through a new engine air cleaner element must not have a restriction of more than the following amount:

Maximum restriction ... 3.7 kPa (15 inch of H₂O)

Exhaust Restriction

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The muffler and converter will become extremly hot during engine operation. A hot muffler and converter can cause serious burns. Allow adaquate cooling time before working on or near the muffler and converter.

Excessive idling can cause the catalytic converter/muffler to plug. A plugged catalytic converter/muffler will lead to an increase in exhaust back pressure. Operating the engine in extremely cold conditions may cause the catalytic converter/muffler to plug. One indication of a plugged catalytic converter/muffler is poor engine response.

If the engine is operated at low idle or at low load for 24 or more consecutive hours, the engine should be run at rated conditions for five to fifteen minutes. Running the engine at rated conditions should clean out the catalytic converter/muffler.

Exhaust Back Pressure

Back pressure is the difference in the pressure between the exhaust and the atmospheric air.

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Hot engine components can cause injury from burns. Before performing maintenance on the engine, allow the engine and the components to cool.

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Making contact with a running engine can cause burns from hot parts and can cause injury from rotating parts. When working on an engine that is running, avoid contact with hot parts and rotating parts.

Illustration 3	g01071356
(A) Catalytic converter/muffler (B) 152 mm (6 inches) (C) 305 mm (12 inches) (D) Turbocharger or Exhaust Manifold (5) Preferred Test Location (6) Optional Test Location

The location of the back pressure tap is important in order to obtain an accurate back pressure reading. The test location should be located on a straight length of exhaust pipe. This back pressure tap should be located as close as possible to the turbocharger or the exhaust manifold. The tap should be located at least 305 mm (12 inches) downstream of a bend. The tap should have 152 mm (6 inches) before a bend. If a continuous straight length of exhaust that is 457 mm (18 inches) is not available, the tap should be located as close as possible to the neutral axis on an elbow.

If the exhaust is not equipped with a back pressure tap, the following procedure may be use in order to install a pressure tap.

1. Mark the position for the pressure tap.

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

3. Drill a 3.18 mm (0.125 inch) hole through the wall of the exhaust inside the half coupling.

4. Remove any burrs from the inside of the exhaust pipe.

Use the differential pressure gauge of the 1U-5470 Engine Pressure Group or the 198-4240 Pressure Indicator Tool Gp in order to measure back pressure from the exhaust. Use the following procedure in order to measure back pressure from the exhaust:

Illustration 4	g01071363
(1) Turbocharger (6) Test location (7) Catalytic converter/muffler (8) Exhaust piping

1. Connect the pressure port of the differential pressure gauge to test location. The test location should be located on a straight length of exhaust pipe. This back pressure tap should be located as close as possible to the turbocharger or the exhaust manifold.

2. Leave the vacuum port of the differential pressure gauge open to the atmosphere.

3. Start the engine. Run the engine in the no-load condition at high idle until the engine reaches normal operating temperature.

4. Record the value.

5. Multiply the value from Step 4 by 1.8.

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

Back pressure from the exhaust must not be more than the following amount:

Maximum back pressure for engines without a Catalytic converter/muffler ... 10.0 kPa (40 inch of H₂O)

Maximum back pressure for engines with a 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".

If the back pressure exceeds 14.9 kPa (60 inch of H₂O), replace the catalytic converter/muffler.

Diesel Particulate Filter (If Equipped)

Illustration 5	g01071367
Orientation of the Diesel Particulate Filter (9) Inlet section (10) Catalyst section (11) Filter section (12) Outlet section (13) Test location (14) Tee fitting (15) Copper tubing (16) Thermocouple

Note: Do Not test the exhaust back pressure if the red warning light has been activated. Clean the DPF immediately. Refer to Operation and Maintenance Manual, SEBU7011, "Exhaust Particulate Filter - Clean" for the proper procedure.

1. Connect the pressure port of the differential pressure gauge to test location. The test location is on the Diesel Particulate Filter.

2. Leave the vacuum port of the differential pressure gauge open to the atmosphere.

3. Start the engine and run the engine in the no-load condition at high idle until the engine reaches normal operating temperature.

4. Record the value while the engine is operating at high idle.

5. Multiply the value from 4 by 1.8.

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

Clean the Diesel Particulate Filter if the back pressure exceeds the following value.

... 25 kPa (100 inch of H₂O)

Additional information is available in Operation and Maintenance Manual, "Exhaust Particulate Filter - Clean".