VALVE GP-RELIEF 2705978 - Caterpillar

All Diesel Engines So EquippedThe air fuel ratio control limits the amount of fuel for injection during acceleration. The purpose of the control is to keep the amount of smoke in the exhaust gases at a minimum. When the adjustment of the air fuel ratio control is correct there will be enough fuel for rapid acceleration and there will not be too much exhaust smoke. If the adjustment is not correct, the engine will accelerate too slowly or there will be too much exhaust smoke. Excessive smoke can result in high levels of soot in the engine oil. Tests show that high levels of soot in the oil can shorten the service life of engine bearings and other internal components. Also, high levels of soot will increase the viscosity of the oil and cause early plugging of the engine oil filters. These can result in engine damage.
The operation of the air fuel ratio control is most important in applications that have frequent accelerations and decelerations.
The fuel settings on on-highway truck engines must be adjusted to EPA-approved specifications by a serviceman who has had the necessary training for fuel system maintenance.
To keep smoke and soot at an acceptable level:
1. Use the correct tools and a dial indicator to make sure the air fuel ratio control is set at the specification shown in the fuel setting microfiche. Also, during the adjustment procedure make sure the engine is at normal operating temperature and approximately 800 rpm. This will permit consistent results. Do not try to set the air fuel ratio control visually (without a dial indicator). If the air fuel ratio control is set visually, the setting is usually to high (rich).2. Periodically, check the air fuel ratio control for correct operation. To do this, install a dial indicator to make sure that the setting repeats itself.Some other possible causes for high levels of soot in the engine oil are: 1. A restriction in the air intake or exhaust system.2. Extended oil and filter change intervals.3. Worn pistons rings and cylinder liners.4. Excessive fuel settings.5. Wrong fuel.6. A turbocharger which does not operate correctly.