2.1.1 Fuel Injector
DETROIT DIESEL 53
2300 and 3300 psi. The opening and closing action
should be sharp and produce a finely atomized spray.
If the valve opening pressure is below 2300 psi and/or
atomization is poor, the cause usually is a worn or
fatigued valve spring. Replace the spring.
If the valve opening pressure is within 2300-3300 psi,
proceed to check for spray tip seat leakage. Actuate the
pump handle several times, then hold the pressure at
1500 psi for 15 seconds. Inspect the spray tip seat for
leakage. There should be no fuel droplets although a
slight wetting of the end of the valve tip is permissible.
If the spray tip seat is satisfactory, proceed to check the
hold time for a pressure drop of from 1500 to 1000 psi.
The time should not be less than 5 seconds. If the valve
pressure drops from 1500 to 1000 psi in less than 5
seconds, replace the needle valve and tip assembly.
Fig. 20 - Position of Calibrator Fuel Flow Pipes
If the needle valve assembly passes the above test, the
needle valve lift check can be omitted. To check the
indicates the spray tip and needle valve assembly must
needle valve lift , use tool J 9462-01 (Fig. 15.) as
Reassemble the injector as outlined under Assemble
1. Zero the indicator by placing the bottom surface of
Injector and check it in the comparator or the calibrator.
the plunger assembly on a flat surface and zero the
FUEL OUTPUT TEST
The injector fuel output test can be performed in either
2. Place the spray tip and needle valve assembly tight
the comparator J 7041 or the calibrator J 22410.
against the bottom of the gage with the quill of the
needle valve in the hole in the plunger.
When injectors are removed from an engine for fuel
output testing and, if satisfactory, reinstalled without
3. While holding the spray tip and needle valve
disassembly, extreme care should be taken to avoid
assembly tight against the gage, read the needle valve
reversing the fuel flow. When the fuel flow is reversed,
lift on the indicator. The lift should be .008 " to .018 "; if
dirt trapped by the filter is back-flushed into the injector
it exceeds .018 ", the tip assembly must be replaced. If
it is less than .008 ", inspect for foreign material
between the needle valve and the tip seat.
Before removing an injector from the engine, note the
direction of the fuel flow. To avoid reversing the fuel
4. If the needle valve lift is within the limits, install a
flow when checking injector fuel output, use the
new needle valve spring and recheck the valve opening
appropriate adaptor. The position of the fuel pipes on
pressure and valve action. Low valve opening pressure
the comparator (Fig. 16.) depends on the adaptor being
or poor atomization with a new spring and seat
used and the direction of fuel flow through the injector.
The position of the braided fuel inlet tube and the plastic
FUEL OUTPUT CHECK CHART
fuel outlet tube on the calibrator (Fig. 20.) depends on
J 22410 Calibrator
J 7041 Compactor
the adaptor being used and the direction of fuel flow
through the injector.
The fuel passages in
Fig. 19. - Fuel Output Check Chart
adaptors J 7041-61, J-7041-72 and J
7041-88 are drilled straight
1972 General Motors Corp.