provided. All pump tests should be made with the testing
fuel oil temperature between 90°F and 100°F. Now you
are ready to conduct the test.
Open the fuel shutoff valve and manifold orifice
valve. Open the stand throttle, start and run the pump at
500 rpm until the manifold pressure gauge shows the
recommended pressure. If the pump does not pickup the
specified pressure, check for closed valves in the suction
line or an air leak.
If the pump is newly re-built, run it at 1500 rpm for
5 minutes to flush the pump and allow the bearings to
seat. Continue to run the pump at 1500 rpm and turn the
rear throttle stop screw in or out to find the maximum
manifold pressure at full throttle.
With a standard governed pump, the
throttle screws will be readjusted later. If the
pump has a variable speed governor, the throttle
shaft is locked in full-throttle position; do not
readjust. On a dual or torque converter governor
pump, the throttle must be locked in the shutoff
position and the converter-driven governor
idle-adjusting screw turned in until the spring is
compressed. The converter-driven governor
must be set on the engine.
The pump idle speed is set by closing the bypass and
manifold orifice valves and opening the idle orifice
valve. Set the pump throttle to idle and run at 500 rpm.
To decrease or raise the idle pressure, add or remove
shims from under the idle spring. Remember not to set
the idle screw until you have adjusted the throttle
Once the tests and adjustments have been completed
according to the specifications recommended by the
manufacturer, remove the pump from the test stand.
Make sure the suction fitting is not removed or
disturbed. Next, loosen the spring pack cover and drain
the pump body. Cover all openings and bind fittings with
tape until you are ready to install the pump.
Injector Maintenance and Testing
In the PT fuel system, fuel is metered by fuel
pressure against the metering orifice of the injector. Any
change in fuel pressure, metering orifice, or timing will
affect the amount of fuel delivered to the combustion
chamber. The following two things will interfere with
the normal functions of injector orifices:
1. Dirt or carbon in the orifices or in the passages
to and from the orifices; and
2. A change in the size or shape of the orifices,
particularly caused by improper cleaning of the orifices
After soaking dirty injectors in a cleaning solvent to
remove the carbon, be sure to dip the injectors in a
neutral rinse, such as mineral spirits, and then dry them.
Never use cleaning wires on PT fuel
Be sure to use a magnifying glass to inspect the
injector orifices for damage. When the injector orifices
are damaged, they cannot be made to function properly
and must be replaced.
Check the injector for a worn plunger or injector
body. Worn injectors may cause engine oil dilution from
excessive plunger to body clearances. Dilution may also
result from a cracked injector body or cup or a damaged
O ring. To check the injector for leakage, assemble it.
Remember to plug off the injector inlet and drain
connection holes; then mount the injector on the injector
Test the injector at a maximum of 1000 psi with the
fuel flowing upward through the cup spray holes. If the
counterbore at the top of the injector body falls with fuel
in less than 15 seconds, the plunger clearance is
excessive and may cause engine oil dilution. During this
check inspect the injector for leaks around the injector
cup, body, and plugs. If the injector does not pass the
test and checks, remove the damaged parts and replace
them with new parts.
Any time you remove an injector plunger, use the
lubricant recommended by the manufacturer when you
replace the plunger in the injector body.
If the injector plunger does not seat in the injector
cup, change the cup rather than trying to lap the plunger
and cup together. Lapping changes the relationship
between the plunger groove and metering orifice and
disturbs fuel metering. Always use a new injector cup
gasket when you assemble the cup to the injector body
to avoid distortion of the cup. When the cup is tightened
to the injector body, the gasket compresses everywhere,
except under the milled slot on the end of the injector
body. Then, if the gasket is reused, the uncompressed
areas may cause the injector cup to cock and prevent the
injector plunger from seating properly.