TRUCK SERVICE MANUAL
a. Note position of throttle l eakage adjusting screw.
when throttle is opened after down grade closed throttle
motoring and prevents the engine from stalling when it
b. Back screw out while checking engine deceleration
decelerates to idle.
as described previously until engine tends to stall after
decelerating from hi-idle. Turn screw in until deceleration time
a. Excessive throttle leakage will cause engine to
is increased 1 to 2 seconds. Lock screw in position and check
decelerate too slowly.
idle speed. Adjust idle speed as required.
b. Insufficient throttle leakage will cause engine
response hesitation after closed throttle motoring and stalling
after decelerating to idle.
Adjusting Dual Power Torque Limiting Valve
Note: If throttle leakage is adjusted correctly on fuel pump
This valve must be adjusted when engine is on a
dynamometer.
test stand, adjustment after fuel pump installation on engine is
not required.
1. When fuel pump is calibrated, the valve solenoid is
energized or valve adjusting sleeve is bottomed, allowing full
3. If throttle leakage adjustment on engine is required, it
fuel flow.
should be performed in the following manner.
2. Normal engine testing may be completed with valve
4. Engine must be operated long enough to purge all air
locked open in this manner.
from fuel system and at operating temperature.
3. To adjust valve, remove aneroid fuel lines and plug
CAUTION
holes, remove valve solenoid wires and remove sealing plug
Never check engine deceleration or adjust throttle leakage
from front of valve body.
on a cold engine. Engine will decelerate faster when cold
due to greater friction drag.
4. With solenoid De-energized,
start
engine
and
increase speed to high idle.
5. Vehicle throttle linkage must be adjusted so pump
throttle just contacts the front throttle stop screw when throttle
5. Apply load on dyno until 1200 rpm is reached. Adjust
is closed.
valve sleeve until your application specification is obtained.
6. Install valve sealing plug and record value ob tained
6. A fuel manifold pressure gauge must not be in use.
7. Connect solenoid wires, remove aneroid plugs and
replumb aneroid.
7. A stop watch or other suitable timer and tachometer
8. Recheck engine power at rated speed.
must be used to perform the following check.
Engine Power
8. With transmission in neutral or clutch disengaged,
open throttle fully and let engine run at hi-idle (maximum no
1. Engine power cannot be gauged accurately in any
load speed).
way except on an engine dynamometer. Any other method of
gauging engine power requires the use of assumptions, feel,
a. Release or move throttle to closed position quickly
opinions regarding accessory drive train power losses and
and start stop watch simultaneously.
load measuring equipment accuracy.
b. Stop the stop watch when engine reaches 1000 rpm
and note deceleration time. Repeat several times.
2. Fuel pump adjustments should not be made based
c. If engine begins to stall (idle governor does not catch
on estimated power arrived at by this means unless full
engine) after decelerating from hi-idle, throttle leakage must
performance data (fuel manifold pressure, fuel rate, speed
be increased.
settings,
smoke,
coolant
temperature,
smoothness, exhaust restriction, fuel quality, air intake
(1) Note position of throttle leakage adjusting screw
restriction, crankcase oil level and engine power derate
(front throttle stop screw).
factors) also indicates the adjustments are justified. Under no
circumstances should these specifications be exceeded.
(2) Turn screw in while checking engine deceleration as
described previously until deceleration time is increased 1 to 2
seconds. Lock screw in this position and recheck idle speed.
Note: As in all fuel systems and engine performance checks,
Readjust as necessary.
accurate instruments must be used.
9. If engine decelerates too slowly, it may be necessary
3. Engine rated power (maximum power at engine rated
to decrease throttle leakage. Before decreasing throttle
speed) should be checked in the same way as "checking and
leakage, be sure it is required by first checking deceleration
adjusting engine fuel manifold pressure" and "checking and
time when shutdown valve is closed (engine is shutdown)
adjusting engine fuel rate" as previously described.
while running at hi-idle. If deceleration is no faster by this
4. Check governor cutoff setting to assure this is not
method, throttle leakage is not the problem. If deceleration is
influencing rated power
significantly faster by this method, throttle leakage should be
reduced.
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