Probable Causes
- Incorrect air/fuel ratio
- Calibration of the O2 sensors
- Coolant temperature sensor
- Intake manifold air temperature sensor
- Intake manifold pressure sensor
Recommended Actions
Incorrect Air/Fuel Ratio
An air/fuel mixture that is too lean will have an adverse effect on engine operation. Verify that the exhaust emissions are correct. For information on tuning the air/fuel ratio and on adjusting the fuel actuator, refer to Testing and Adjusting, "Air/Fuel Ratio Control - Adjust".
A change in the fuel energy content will change the air/fuel ratio. Obtain a fuel analysis for the fuel supply.
The fuel supply pressure must be adequate and stable. Ensure that the fuel pressure is within specifications.
Calibration of the O2 Sensors
If any of the O2 sensors that measure the exhaust emissions become out of calibration, the air/fuel ratio will be out of specifications. Confirm that the sensor calibration for each of the O2 sensors is correct.
Be sure to use an accurate exhaust analyzer for these measurements.
Coolant Temperature Sensor
A coolant temperature sensor that is producing an incorrect signal will have an adverse effect on the air/fuel ratio. Verify that the sensor is producing the correct signal. Use a 4C-6500 Digital Thermometer in order to check the coolant temperature of the engine near the coolant temperature sensor. Compare the reading with the value that is displayed on the Caterpillar Electronic Technician (ET). Replace the sensor, if necessary.
Note: Be sure to use an accurate thermometer for your measurements. Use of gauges that are not properly calibrated can lead to an improper diagnosis of the problem.
Intake Manifold Air Temperature Sensor
An intake manifold air temperature sensor that is producing an incorrect signal will have an adverse effect on the air/fuel ratio. Verify that the sensor is producing the correct signal. Measure the temperature of the intake manifold air with a thermometer. Compare the reading with the value that is displayed on the Caterpillar Electronic Technician (ET). Replace the sensor, if necessary.
Note: Be sure to use an accurate thermometer for your measurements. Use of gauges that are not properly calibrated can lead to an improper diagnosis of the problem.
Intake Manifold Pressure Sensor
An intake manifold pressure sensor that is producing an incorrect signal will have an adverse effect on the air/fuel ratio. Verify that the sensor is producing the correct signal. Measure the intake manifold pressure with a gauge. Compare the reading with the value that is displayed on Cat ET. Replace the sensor, if necessary.
Note: Be sure to use an accurate gauge for your measurements. Use of gauges that are not properly calibrated can lead to an improper diagnosis of the problem.