Figure 5-16.-Gauge installed for checking transfer pump pressure.
Since most tests are more conveniently made
under no load conditions, all possible readings are
determined at high idle. If the supply pressure is
lower than normal, an engine can still operate
smoothly at approximately the correct high-idle
speed. The governor opens the metering valve
further to make up for the lower pressure;
therefore, you can take successful readings at high
First, disconnect the throttle linkage. Then,
with the engine running, hold the throttle lever all
the way to the rear. Adjust the high-idle stop
screw until the specified high-idle speed is
obtained to test the fuel pressure at high idle.
Install the gauge
assembly in the pressure trap of the transfer
pump, as shown in figure 5-16. If this reading does
not fall within the prescribed range, the pump will
not deliver sufficient fuel to obtain full power
under load. The most common causes of low
pressure are restricted fuel supply, air leaks on
the suction side of the pump, worn transfer pump
blades, or a malfunctioning regulator valve.
To test for excessive pressure (fig. 5-17),
remove the injection fuel pump timing plate. Be
sure you make a small hole in the timing plate
gasket as you install the gauge on the pump. This
hole allows pump pressure to reach the gauge as
you operate the engine at both low
Figure 5-17.-Testing pump housing pressure.