TRUCK SERVICE MANUAL
4. Replace pipe plug when idle speed is correct.
Engine Hi-idle or Maximum No-Load Speed
1. Operate engine to purge all air from fuel system arind
7. Some problems with excessive vibrations have
bring up to operating temperature.
occurred at engine idle speeds particularly in truck
2. With transmission in neutral or the clutch disengaged,
applications that also have power takeoffs.
open throttle and hold fully open. Note the inaxilLimum engine
particularly true of applications with cement mixers.
speed. This speed will be 10 to 12% greater than the
governor "cutoff" speed, depending upon engine parasitic
8. In these cases it has been found that a substantial
loads (fans, pumps, etc.)
amount of vibration can be eliminated by an adjustment of
3. This check should not be used to check or make
the engine idle speed to compensate for component cyclic
governor speed adjustments. This check is of secondary
vibrations p)resent In each particular application.
importance and must be considered as such unless the no-
load speed is significantly greater than specifications in which
9. These are recommended speeds and are intended as
case the governor assembly should be examined for
reference points. Slight deviations can be made from these
malfunction or improper parts.
speeds although it should be noted that extreme care must be
taken so that new problems are not created by extreme
Checking and Adjusting Fuel Manifold Pressure
variations in idle speed.
Listed below are three methods of checking fuel manifold
10. Problems such as difficult gear engagement can be
pressure. The engine must be at operating temperature and
encountered with excessively high idle speeds. Poor load
fuel system purged of all air.
pickup can be a problem if idle speeds are adjusted to low.
1. The preferred method of checking engine manifold
12. Before concluding that the governor plunger is the
pressure is to load engine on an engine or chassis
cause of idle surge, check the weight assist protrusion against
dynamometer as follows.
a. Check governor cutoff as detailed previously.
1. A means of loading the engine must be used to
b. At full throttle, increase load until engine is pulled
perform in this check. The tachometer and fuel manifold
down to rated speed (accurate tachometer must be used).
pressure gauge must be of high accuracy. The engine fuel
Read fuel manifold pressure. If engine fuel manifold pressure
system must be purged of all air and at operating temperature.
is below minimum or above maximum specifications, make the
2. The preferred method of checking governor setting is
to "load" the engine on an engine or chassis dynamometer.
To Raise Pressure
3. Maximum engine speed is adjusted by adding or
(1) Screw out maximum throttle opening stop screw and
removing shims under the high speed governor spring.
utilize throttle restriction thay may be present.
Normally, this adjustment is made on the fuel pump test stand
as the fuel pump is calibrated and does not need to be
changed on the engine.
Do not screw the screw out beyond maximum throttle
opening point otherwise a dead throttle travel may occur.
1. At full throttle increase load until the speed is )pulled
(2) Remove throttle shaft and add fuel adjusting shims as
down to at least 100 rpm below engine rated speed, then
required. To Decrease Pressure (1) Remove throttle shaft and
decrease the load gradually while observing the fuel manifold
remove shims as required.
pressure gauge. (The fuel manifold pressure will increase with
decreasing load until the governor begins restricting fuel and
then the pressure will begin decreasing with decreasing load.)
Under no circumstances should engine manifold pressure
be set above maximum specifications. Doing so will void
2. Continue decreasing load until fuel manifold pressure
reaches its peak and decreases 1 to 2 psi. This is the so
called "governor goes dead", "governor break or "governor
(2) It should not be necessary to adjust fuel manifold
cutoff" point. This speed is between 30 to 50 rpm higher than
pressure on a newly calibrated pump more than + 2 psi [0.14
engine rated speed to assure that governor restricting before
kg/sq. cm]. If adjustments greater than this are required, fuel
rated speed. (Example1 on a 2100 rpm engine this speed
pump test, injector test stand or engine problems may exist.
should be 2130 to 2150 rpm.)
2. The next best method of checking maximum engine
3. If the governor cutoff point is higher or lower than
fuel manifold pressure is to note maximum pressure while
specifications, shims should be removed or added from behind
accelerating at full throttle when going up through the
governor high speed spring accordingly.
transmission ratios. With proper gauge snubbing, this method
can be relatively accurate, especially if a heavy load
4. Recheck the governor cutoff point adjustment.