6. BENCH TESTING THE METERING
Having made the initial adjustments, the
metering unit is tested to check the fuel output over the full operating range
(including maximum and minimum requirements).
The output requirements of the metering unit vary with the vehicle to which it
is fitted, so ensure that it is checked against the correct figures.
If the output performance does not conform to
specification, the metering unit requires recalibrating. The adjustment of the
calibration screws affects the fuel output and hence the performance of the
vehicle (see Figures 24 and 25).
(a) Testing Procedure
(i) Bolt the metering distributor to the
drive flange of the test bench. Ensure that the unit is mounted in the same
position as on the vehicle. (Control datum track should be vertical). Remove
rectangular cover plate.
(ii) Connect outlet unions to injector
(iii) Connect measuring glass to leak off
drain. Connect fuel supply to inlet connections.
Note: Test fuel should be Fawley White
Spirit No. 100; plus 50 parts per million Santoline ‘C’ inhibitor, or
Shell Calibrating Fuel ‘C’.
(iv) Switch on test bench and gradually
increase speed to 1000 rev/mm. Operate overfuel lever several times over
full movement. Check that there is approximately the same amount of fuel in
each sight glass. Fuel should be dripping from the leakage drain.
This check proves that there are no obvious
faults such as leaking or blocked pipes etc. It also ensures that all air is
removed from the pipes.
(v) Connect a variable vacuum supply 0-28”
Hg (711.2 mm) to the control unit depression chamber. Increase vacuum to
approximately 25” Hg (635 mm) and then reduce to zero. Repeat this at
least five times to eliminate any “sticking” in the depression chamber or
on the datum track.
(vi) Check that there is a clearance of 0.004-0.008” (0.10-0.20 mm)
between overfuel lever and adjustment screw which bears on the cam.
(vii) Maintain speed of test bench at 1000
rev/mm, and fuel supply pressure at 100 lbf/in2 (689.50 kN/m2).
Check performance of metering distributor/control unit.
Adjust vacuum to minimum figure in specification tables, and check the
amount of fuel delivered to each sight glass.
Then, adjust vacuum to next figure in the table, and again check amount
of fuel delivered.