2012/04/24 Caterpillar

Engine:

G3516C (S/N: TJB1-UP; TJC1-UP; GZZ1-UP; RWA1-UP; DKR1-UP)

G3516E (S/N: GAS1-UP; SLY1-UP; GHP1-UP)

G3520C (S/N: MAD1-UP; GZJ1-UP; GZK1-UP; GZL1-UP; GZM1-142,149-UP; B9P1-UP; HAT1-UP; CWY1-200,204-206,208-218,222-UP; GDB1-38,42-44,46-UP; GHC1-UP; JBX1-UP; JBZ1-UP)

G3520E (S/N: GZG1-UP; GZH1-UP; HAL1-UP; SXY1-UP; GHM1-UP; GHR1-UP)

Illustration 1	g03013859

Turbocharger surge is typically due to changes in ambient conditions but ambient conditions are not the only factor causing the surge. This condition occurs mainly in cold ambient conditions. A symptom of turbocharger surge is sudden fluctuations in the manifold air pressure. Surging generally occurs when the engine is above 50 percent load. Noise from the turbocharger may be present while the turbochargers surge.

The turbocharger surge is caused by an increase in the pressure across the turbochargers. Turbocharger boost increases allowing the engine to maintain the higher manifold pressures at lower throttle positions. A reduction in the throttle position for a given manifold air pressure reduces the air flow through the compressor side of the turbocharger. When the air flow through the compressor decreases enough, the turbocharger compressor will surge. When, the turbocharger surge occurs the air flow through the compressor can reverse. A sudden drop in manifold air pressure is the result. Refer to Illustration 1. The turbocharger surge can be diagnosed by measuring the differential pressure across the throttle. The differential pressure across the throttle must be measured on an engine when the turbocharger surge is suspected.

Procedure to adjust the Compressor Bypass Valve

Perform the adjustment procedure only if the turbocharger surge occurs. Adjustment is not typically needed.

For normal service, follow the engine Disassembly and Assembly manual.

The compressor bypass valve must be adjusted in order to achieve a pressure differential across the throttle of 40 ± 10 kPa (5.8 ± 1.5 psi). The procedure must be performed in the coldest ambient temperature in the engines operating range. Use the following procedure to adjust the pressure differential across the throttle.

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Illustration 2	g03013906
(1) 162-0177 Plug As

1. Install the pressure differential gauge.

   1. Stop the engine and remove one of plugs (1) from the bottom of the 206-4168 Housing. Refer to Illustration 2.
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   Illustration 3	g03013936
   (2) 9S-8004 O-Ring Plug

   2. Remove plug (2) from the 200-6543 Cover. Refer to Illustration 3.

   3. Install a differential pressure gauge between the holes for plugs (1) and (2) .

   4. Start the engine.

   5. Apply a load to the engine until the full rated load is reached.

      If the engine cannot reach full load due to the turbocharger surge, apply the maximum load to the engine before the turbochargers begin to surge.

   6. Allow the engine power to stabilize at full load for 5 minutes.

   7. Record the reading on the differential pressure gauge.

2. Stop the engine.

   Adjust the compressor bypass valve if the differential pressure is greater than 40 ± 10 kPa (5.8 ± 1.5 psi).

3. Ensure that the engine control switch is in the STOP position.

   The Electronic Control Module (ECM) and the actuator for the compressor bypass must be active, keeping the bypass actuator in the home position.

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The linkage can move and form a pinch point which can cause personal injury. Keep hands away from the linkage.

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Illustration 4	g03014036
(3) Roll Pin (4) Set Screw (5) Nut

Note: The flats on nut (5) are 60 degrees from each other.

4. Mark the location of roll pin (3) on nut (5) as a reference. Rotate the shaft of the valve in the clockwise direction in relationship to the engine flywheel. The roll pin will move in the upward direction. Adjust the valve until approximately 22.5 degrees between the reference mark on nut (5) and roll pin (3) .

   Adjusting the valve 22.5 degrees will slightly open the compressor bypass valve. Opening the bypass valve will lower the differential pressure across the throttle. A small adjustment of the bypass valve will have a large effect on the differential pressure of the throttle. If, the bypass valve is adjusted too much the throttle will go to the 100 percent position before the engine reaches rated load. Throttle position will change due to the loss of boost pressure.

5. Tighten set screw (4) to 15 ± 1 N·m (11 ± 0.7 lb ft).

6. Check the differential pressure.

7. Repeat the procedure until the differential pressure is 40 ± 10 kPa (5.8 ± 1.5 psi).

8. Remove the differential pressure gauge and reinstall the plugs.

9. Ensure that the engine meets emissions requirements. Adjust the governor in order to maximize power stability.