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5.4.
FUEL SYSTEMS
The vacuum tester can be used to evaluate the condition of a mechanical fuel pump by testing the vacuum that it is able to create. Locate
and remove the suction line from the pump. connect the vacuum tester to the suction port of the pump, start and run the engine at idle.
The vacuum reading that should be observed will vary slightly on different makes and models but as a general rule approximately 15inHg
of vacuum should be created. This should also be held for approximately 1 minute after engine shut down. If this vacuum reading is not
achieved or the vacuum drops off immediately with the engine shut down, the fuel pump requires either overhaul or replacement.
5.4.1.
CARBURETTORS
5.4.1.1.
There are many different types of vacuum control systems used on carburettors. Using the vacuum tester kit allows quick and accurate
testing of these systems. Listed below are just two examples of tests that can be carried out.
5.4.1.2.
Testing a Choke Break Diaphragm. With the engine at normal operating temperature but not running, disconnect the vacuum line to the
diaphragm module. Connect the vacuum tester (fig.3) and apply approximately 15inHg of vacuum and wait for 30 seconds. No drop in
gauge reading should be observed. With the vacuum still applied ensure that the choke butterfly is pulled to the fully open position.
5.4.1.3.
Testing Vacuum Operated Carburettor Secondary Barrel. With the engine at normal operating temperature but not running, remove the
vacuum line from the secondary diaphragm module. Connect the vacuum tester (fig.4), hold the throttle and secondary air valve flaps
open. Operate the hand pump whilst observing free and easy opening of the secondary throttle butterfly.
5.4.2.
TESTING FUEL INJECTION pRESSURE REGULATOR
5.4.2.1.
Multi-point fuel injection rail pressure must vary to suit changing engine loads and fuel delivery requirements. This is done using a
vacuum operated regulator which is connected to the engine manifold vacuum to sense the varying loads.
5.4.2.2.
To test the fuel rail pressure, a gauge is attached to the rail, then engine loads must be created to vary engine manifold vacuum. Simply
remove and block off the vacuum supply line to the pressure regulator, connect and operate the VS4022 vacuum pump (fig.5) to simulate
vacuum pressures in accordance with the manufacturer's specifications and note variation in fuel pressure reading.
5.4.3.
TESTING EMISSION CONTROL EXHAUST GAS RECIRCULATION VALVES (EGR)
5.4.3.1.
start engine and run at idle until normal operating temperature is reached. remove the vacuum line from the eGr valve and attach the
vacuum tester kit (fig.6). Operate the hand pump to apply approximately 15inHg of vacuum. If the EGR Valve is working correctly the
engine idle will become rough. If the idle remains unchanged the valve is possibly seized in the closed position. If the vacuum is not held,
the diaphragm in the valve has failed.
5.5.
ADDITIONAL VACUUM SYSTEMS
5.5.1.
TESTING ONE-WAY VALVES
5.5.1.1.
Many vacuum operated circuits use in-line one-way valves to apply vacuum in one direction only.
5.5.1.2.
To test the function of the valve remove it from the circuit. Attach the vacuum tester (fig.7) and operate pump to apply vacuum. In one
direction the valve should hold vacuum and in the opposite direction it should not.
5.5.2.
TESTING ELECTRICALLY OpERATED VACUUM SOLENOIDS
5.5.2.1.
electrically operated vacuum solenoids are commonly used in control circuits for air conditioning/ventilation systems, emission control
systems, idle step up systems etc. and testing the function of these when using the VS4022 is extremely simple.
5.5.2.2.
Locate the solenoid to be tested and remove the line that goes to the component being tested. Connect the vacuum tester to the solenoid
port (fig.8) and start the engine. With the system turned off there should be a zero gauge reading. Now turn the system to the 'on' position
and a gauge reading equal to the manifold vacuum should be observed, if no reading exists remove the vacuum supply line and test for
manifold vacuum at this point. If the vacuum does exist this indicates that the solenoid is faulty or it is not receiving a 'switch on' voltage
(use a multimeter to test this). If no vacuum exists trace the supply line back to the vacuum source checking for kinks and breaks.
5.5.3.
TESTING THERMAL VACUUM SWITCHES
5.5.3.1.
there are many vacuum controlled circuits that must only operate when the engine reaches normal operating temperature. this is done
using thermal switches that remain in an 'off' position until a given temperature is reached.
© Jack sealey limited
fig.2
fig.5
Original Language Version
fig.3
VS4022.V2
fig.4
fig.6
Issue 1 17/01/18
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