TRUCK SERVICE MANUAL
is being pulled and engine acceleration in the higher gears is
4. Operate engine at full throttle at setting BHP speed
slow.
shown in Table 521, and adjust bottom screw In aneroid (back
the screw out) until fuel pressure Is reduced the required
3. The least preferred method of checking maximum
amount as calculated under "fuel pump derating," in aneroid
engine fuel manifold pressure is the so called "snap" pressure
section of manual, for particular altitude.
check method.
a. The "snap" method is not as reliable as method 1 and
Note: This can be done by snap fuel pressure readings if
2 because the pressure reading is of very short duration.
necessary but engine loaded method is preferred.
Gauge inertia and/or the degree of throttle manipulation also
reduces the reliability of snap pressure readings.
5. Tighten locknut on adjusting screw and reconnect air
line between aneroid and Intake manifold.
b. To take snap pressure readings, attach the ST435
pressure gauge at the shutdown valve in the usual manner.
Checking and Adjusting Engine Fuel Rate
Fig.531
Engine fuel rate (fuel consumption) in lbs. per hr. is
measured by using ST1190 Flow Rater. Fig. 532 is a typical
installation of checking fuel with ST1190.
1. The fuel rate specified on fuel pump calibration
specifications is at full throttle and rated speed.
2. An engine dynamometer, chassis dynamometer or
other controlled means of loading engine must be used.
Accurate fuel manifold pressure and speed readings must also
be taken.
3. To check engine fuel rate, load engine to full throttle
until engine speed is pulled down to and kept at rated speed
Fig. 531, F5178. Checking fuel manifold pressure
(check governor cutoff speed as previously described while
loading engine). Note fuel manifold pressure at rated speed.
c. Disconnect the vehicle throttle control linkage at the
Hold engine speed and load stable at rated speed long
throttle lever. Move lever clockwise against stop.
enough for the flow meter float to stabilize. Take the fuel rate
reading.
d. Start engine and run engine speed up to 200 to 300
rpm above idle by opening throttle slightly, then snap throttle to
fully open position and permit engine to accelerate to
maximum speed while observing pressure gauge. Note
momentary maximum pressure. Take this reading several
times.
Notes:
(1) Due to its poor reliability and inherent inaccuracy this
check should not be used to gauge fuel pump test stand
calibration accuracy.
(2) On turbocharger engines having aneroid, it is
necessary that fuel routing through the aneroid be blocked or
removed when making snap pressure checks.
Fig. 532. F5247. Checking fuel rate with ST1190
Checking And Adjusting Aneroid Fuel Pressure Setting
Throttle Leakage
1. Plumb an ST435 pressure gauge into injector supply
line (fuel pressure check pipe plug in shutdown valve).
1. The purpose of throttle leakage is to keep fuel lines or
supply drillings and injector drillings full of fuel during closed
2. Operate
engine
until
all
systems
are
up
to
throttle engine motoring.
temperature.
2. Throttle leakage prevents engine response hesitation
3. Disconnect air line between aneroid bellows and
intake manifold.
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