HARNESS AS-ENGINE 5298748 - Caterpillar

Probable Causes
Inlet air restriction
Operation with a light load
Active diagnostic code from the Integrated Temperature Sensing Module (ITSM)
A faulty thermocouple
Insufficient ignition
Low cylinder compressionRecommended Repairs
Inlet Air Restriction
Note: Inlet air restriction can cause uneven exhaust port temperatures. For example, the cylinders at the front half of the engine may have exhaust port temperatures that are 10 °C (50 °F) to 20 °C (68 °F) lower than the exhaust port temperatures for the cylinders at the rear half of the engine. If this occurs, measure the inlet air restriction for each turbocharger. Make repairs in order to equalize the inlet air restriction for both turbochargers.Check for Misfire
Operation with a low load can result in low exhaust temperatures. Operate the engine at low idle or near low idle in order to identify a misfire problem.Troubleshoot the cause of the misfire. Refer to Troubleshooting, "Engine Misfires,Runs Rough or Is Unstable".Check for Diagnostic Codes from the Integrated Temperature Sensing Module (ITSM)
Use the Caterpillar Electronic Technician (ET) to check for diagnostic codes that relate to the thermocouples for exhaust temperatures. Troubleshoot the code.Check for Suspect Thermocouples
Observe the temperatures from the thermocouples after the engine is shut off.When the engine is operating properly, the temperatures from similar locations are reduced at a similar rate. Also, the temperatures from similar locations are comparable.If any discrepancies are found, switch the suspect thermocouple for another thermocouple. If the temperature problem follows the thermocouple, replace the thermocouple.If the temperature problem stays at the original location of the suspect thermocouple, investigate the cause for the low temperature.Check for Insufficient Ignition
Use Cat ET to check for logged diagnostic codes that relate to the ignition system. Troubleshoot the code. Refer to Troubleshooting, "Ignition Transformers Primary Circuit".If no logged diagnostic codes are present for the suspect cylinder, inspect the components of the ignition system for the cylinder. Refer to Troubleshooting, "Ignition Transformers Secondary Circuit and Spark Plugs".Check the Cylinder Compression
Measure the cylinder pressures of the suspect bank in order to check for problems that are related to compression.If low compression is found, investigate the cause of the low compression. Make repairs, as needed.