Troubleshooting Boost Pressure Below Normal

Boost Pressure Below Normal

The probable root causes are listed below:

• Air inlet restrictions
• Fuel supply
• Injector solenoid
• Wastegate
• Engine speed/timing signal
• Low fueling rate
• Active engine derate
• Intermittent sensor problem

Perform the following checks:

1. Check for restrictions in the air inlet system. Refer to Systems Operation, "Restriction of Air Inlet and Exhaust".

2. Check fuel lines for the following problems: restrictions, collapse and pinched line. Repair the lines and/or replace the lines. Refer to Testing and Adjusting, "Fuel System Inspection".
   1. Check the fuel tank for foreign objects which may block the fuel supply. Check for air in the low pressure fuel supply system after you have performed the following procedures:
      • Replace the filters.
      • Work on the low pressure fuel supply circuit
      • Replace the fuel injectors.
   2. Purge air from the low pressure fuel supply circuit with the hand priming pump and by cranking the engine in 30 second cycles. After you crank the engine, stop for two minutes. This will allow the starting motor to cool. Loosen the vent plug at the fuel return. The plug is located on the rear upper left side of the engine block. Hand prime the engine again if air in fuel continues. A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel.
   3. Check fuel quality. In temperatures below 0 °C (32 °F), check for solidified fuel (wax). Refer to Special Publication, SEBD0717, "Diesel Fuels And Your Engine". Check the fuel pressure while the engine is cranking. Check the fuel pressure at the filter. Refer to the Specifications manual for correct pressure values. If the pressure is low, check for plugged fuel filters. If the fuel pressure is still low, check the following items: fuel transfer pump, fuel transfer pump coupling and fuel pressure regulating valve. Check for a problem with the combustion system.

3. Check for active diagnostic codes for the injector solenoids. Check for logged diagnostic codes for the injector solenoids. Perform the Injector Solenoid Test. Observe that the injector solenoids are being energized on the Caterpillar Electronic Technician (ET). Perform the Cylinder Cutout Test. Locate the misfiring cylinder. Refer to the diagnostic functional test Troubleshooting, "Injector Solenoids".

4. Verify that the exhaust bypass valve for the wastegate can close. Use Cat ET to override the wastegate to 0 percent. Perform a torque converter stall test. After 15 seconds, a High Boost Pressure Event should result. If a High Boost Pressure Event occurs, the wastegate is closing properly.

5. Check Cat ET for the following logged Diagnostic Codes 190-02 and 190-08. Refer to the diagnostic functional test Troubleshooting, "Engine Speed/Timing Sensor".

6. Check the fueling rate. Refer to Specifications Manual. If the fuel rate is low, complete the cylinder cutout test.

7. Connect Cat ET and check for "ACTIVE" engine derates. If the active engine derate is due to "Axle Protection", refer to the Service Manual for the transmission or implement control. Perform the torque converter stall test. Compare the achieved stall speed to specifications. If the output meets specifications, continue with diagnostic checks.

8. Check for any recently logged diagnostic codes. Check the connectors and wiring for any signs of damage. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".

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