SWITCH AS-TOGGLE 1140421 - Caterpillar

Truck Engines (92U) With Direct Injection And TurbochargerSome 3406 Truck Engines have had problems with low idle instability (rpm that is not constant). Generally, an increase in the low idle rpm to 750 rpm will prevent this instability at low idle.
The specification for low idle has been changed from 700 rpm to 750 rpm on 3406 Truck Engines. This is in effect with Serial Number 92U42026. If low idle instability is still a problem, use the procedure that follows.
1. Start the engine and run it until it gets to normal engine temperature2. Check the low idle rpm.3. Increase the throttle to high idle rpm, and then let it come back to low idle rpm.4. If the rpm slowly increases 20 rpm or more above the original setting, increase the low idle setting 10 rpm.5. Do Steps 3 and 4 again until the rpm increase is no more than 10 rpm, or until the rpm increases suddenly with only a small turn of the low idle screw. This is the real point of stability (constant rpm). This point of stability must be no greater than 800 rpm. If you can not get rpm stability at 800 rpm or less, the governor servo mechanism can be removed and disassembled. Carefully remove any burrs found on the piston assembly, cylinder, etc. with very fine emery paper.