821979 Mercury NUT

Recommended Actions
Table 1
Troubleshooting Test Steps Values Results
1. Check Derate or High Altitude Operation
A. Connect Cat® Electronic Technician (ET) and check for logged events that derate engine power. An engine derate indicator will appear on Cat ET if an active engine derate is occurring.
Note: The following conditions may cause an engine derate that is not annunciated to the operator.
B. The Electronic Control Module (ECM) monitors the following parameters to calculate a value for the exhaust temperature of the engine:
- Intake manifold air temperature
- Atmospheric pressures
- Engine speed
Note: High intake manifold air temperature, high altitude operation, and/or high engine speeds at high load can cause the exhaust temperature to increase. The exhaust temperature may be allowed to increase to a level that may damage the components of the exhaust system. If the conditions warrant, the ECM may derate the engine power to prevent this calculated temperature. The engine derate will avoid potential damage to these engine components.
During an engine derate that is initiated for this calculated temperature, two histograms will begin recording data. The histograms record intake manifold air temperatures and atmospheric pressures. The histogram data will be recorded by the ECM only while the engine derate is active. Use Cat ET to view the histogram data to assist in troubleshooting a low-power complaint.
Check the engine fan system to make sure that the fan is working correctly.
Perform the following procedure:
1. Determine the operating conditions of the engine. Interview the operator, when possible. Determine if an excessive load was placed on the engine during the low-power complaint. Determine if the engine is operating at a high altitude.
If the engine derate is due to normal engine operation, review the histograms for intake manifold air temperatures and atmospheric pressures. This data will help to determine the cause of the engine derate.
2. Check the aftercooler core for debris.
The intake manifold air temperature can increase if the aftercooler is obstructed. Check the fins of the aftercooler for obstructions. If the fins of the aftercooler are obstructed, clean the fins. Return the engine to service.
3. Check the 5 V supply to the atmospheric pressure sensor and the turbocharger compressor inlet pressure sensors.
If the supply is lost for these sensors, the sensor output will float to a value that is within the operational range of the sensor. The ECM detects this nominal value as a low barometric pressure. The ECM interprets this low barometric pressure as a high altitude condition. The engine is then derated by the ECM for the high altitude condition.
Derate or Altitude
Result: The engine is not operating at a high altitude.
Proceed to the next step.
Result: The engine is operating at a high altitude.
Repair: Make sure that the settings for the engine are correct for the altitude.
If the