74257A 3 Mercury PLATE ASSEMBLY, DRIVE SHAFT HOUSING

Introduction
Use this Special Instruction to troubleshoot elevated exhaust temperatures that can damage the exhaust system and shorten the life of the exhaust tube after a field repair.Description of the Problem
Some machines with the 3408E and the 3412E engines have experienced repeat failure of the exhaust tube between the exhaust manifold and turbocharger exhaust housing after a field repair. These failures are due to excessive temperatures in the exhaust system.Excessive exhaust temperatures will cause damage and/or warping of the exhaust manifold which will result in misalignment during assembly, exhaust leakage and repeat failure of the exhaust tube. Exhaust temperatures must be returned to acceptable levels, and damaged or warped components in the exhaust manifold assembly must be replaced prior to replacing the exhaust tube in order to prevent repeat failure of the exhaust tube.Normal or Expected Exhaust Temperatures
Note: The values that are listed in the following table pertain to operation at sea level.
Table 1
Peak Exhaust Temperature     Engine Speed    
600 °C (1112 °F) to
650 °C (1202 °F)     2000 rpm    
650 °C (1202 °F) to
700 °C (1292 °F)     1200 rpm to 1300 rpm    Note: Exhaust temperatures may increase 60 °C or 108 °F during operation in higher ambient temperatures and/or during operation in higher altitudes (above 1000 m (3300 ft)).When exhaust temperatures reach 760 °C (1400 °F) troubleshooting and repair are required to avoid shortened life of the exhaust tube.Measurement of High Exhaust Temperatures
Note: Measure exhaust temperatures during normal working operation or during a torque converter stall condition at full load with the engine at the proper operating temperature. Set the sample rate to one per second for period of at least 30 minutes.Note: Reference the engine serial number in the Technical Marketing Information System (TMI) for the proper nominal engine fuel rate and turbocharger boost pressure at rated torque and peak torque.A typical test could include the following data sampling. Use the Caterpillar Electronic Technician (Cat ET) and the 131-5051 DataView Tool Gp to collect the data. Use an exhaust 4C-6268 Probe in the turbocharger Y manifold ports (right bank and left bank) to measure the exhaust temperature. Use a rate of burn 179-0710 Meter Group to measure the engine fuel rate.Monitor the status of the following conditions on Cat ET:
Boost pressure
Engine speed
Desired engine speed
Load factor
Calculated fuel rate
Max fuel limit
FRC limitMonitor the following Dataview channels:
Fuel flow rate
Exhaust temperaturesThe following illustrations are examples of screens from Cat ET:
Boost and load factor
Fuel consumption rate and injection duration
Desired engine speed and the actual engine speed
The fuel position and the rated fuel limit
Engine coolant temperature and fuel temperature
Illustration 1 g01164814
Boost and load factor for Cat ET
Illustration 2 g01164317
Engine fuel consumption rate and injection duration for Cat ET
Illustration 3 g01164492
Desired engine speed and the actual engine speed for Cat ET
Illustration 4 g01164574
The fuel position and the rated fuel limit for Cat ET
Illustration 5 g01164810
Engine coolant temperature and fuel temperature for Cat ET
Illustration 6 g01164575
Left and right exhaust temperatures for Data-View
Illustration 7 g01164771
Boost pressure and fuel pressure for Data-View
Illustration 8 g01164496
Fuel consumption for Data-ViewCompare Collected Data to Normal Values
The peak exhaust temperatures can be compared with the expected temperatures that were noted earlier. The fuel flow rate can be compared to the nominal fuel flow rate that is listed in the TMI. The boost pressure can be compared to the values for the boost pressure that are listed in the TMI. The measured boost pressures must be above nominal levels or below nominal levels by more than 14 kPa (2 psi) in order to be considered significant. Significant deviations of the engine performance from the nominal levels (high fuel rate or low boost) can provide helpful indications of the root cause for the high exhaust temperature.Slight adjustments of the fuel rate may also be necessary in order to compensate for engine speed, the load factor, and the altitude.To find the Corrected Fuel Rate (FR), divide the Actual FR by the