Horsepower requirements on an engine may vary due to fluctuating loads. Therefore, some method must be
provided to control the amount of fuel required to hold the engine speed reasonably constant during load
fluctuations. To accomplish this control, a governor is introduced in the linkage between the throttle control and
the fuel injectors.
Engines subjected to varying load conditions that require an automatic fuel compensation to maintain a near
constant engine speed, which may be changed manually by the operator, are equipped with a variable speed
Check Governor Operation
Governor difficulties are usually indicated by speed variations of the engine. However, it does not necessarily
mean that all such speed fluctuations are caused by the governor. Therefore, when improper speed variations
are present, check the engine as follows:
1. Make sure the speed changes are not the result of excessive load fluctuations.
2. Check the engine to be sure that all of the cylinders are firing properly (refer to Troubleshooting). If any
cylinder is not firing properly, remove the injector, test it and, if necessary, recondition it as outlined in Fuel
3. Check for bind that may exist in the governor operating mechanism or in the linkage between the governor
and the injector control tube.
With the fuel rod connected to the injector control tube lever, the mechanism should be free from bind
throughout the entire travel of the injector racks. If friction exists in the mechanism, it may be located and
corrected as follows:
1. If an injector rack sticks or moves too hard, it may be due to the injector holddown clamp being too tight or
improperly positioned. To correct this condition, loosen the injector clamp, reposition it and tighten the clamp
bolt to 20-25 lb ft (27-34 Nm) torque.
2. An injector which is not functioning properly may have a defective plunger and bushing or a bent injector
rack. Recondition a faulty injector as outlined in Fuel Injector.
3. An injector rack may bind as the result of an improperly positioned rack control lever. Loosen the rack
control lever adjusting screws. If this relieves the bind, relocate the lever on the control tube and position the
rack as outlined in Engine Tuneup.
4. The injector control tube may bind in its support brackets, thus preventing free movement of the injector
racks to their no-fuel position due to tension of the return spring. This condition may be corrected by loosening
and realigning the control tube supporting brackets. If the control tube support brackets were loosened,
realigned and tightened, the injector racks must be repositioned as outlined in Engine Tuneup.
5. A bent injector control tube return spring may cause friction in the operation of the injector control tube. If
the spring has been bent or otherwise distorted, install a new spring.