4.3.
Ignition system Vacuum Advance
4.3.1. on standard points systems and some electronic ignition systems there are two types of advance methods used, both of which must function correctly to
obtain maximum performance and fuel economy.
4.3.2. the first method Is
Mechanical
or
centrifugal
, which operates by the use of weights located in the base of the distributor. the weights move outwards
advancing ignition timing as engine rPM increases. this is tested by firstly removing the vacuum advance line to disable the system, then with a timing light
connected, run the engine rPM up checking that the timing advances in accordance with the manufacturer’s specification.
4.3.3. the second method is
Vacuum Advance
, which senses engine load via manifold vacuum. A vacuum diaphragm is mounted onto the distributor and
connected to a rotating internal base plate which advances or retards timing as required to suit varying engine loads. to test this system for correct
operation, again with the timing light connected, raise the engine rPM and check timing advance against manufacturer specifications. In the event that the
vacuum advance is not operating, remove the vacuum line from the distributor advance mechanism. connect the Vs4021 (fig.2) and create a 5-10inHg
vacuum, monitoring the timing at the same time. If a timing advance is noted this confirms that the vacuum diaphragm and mechanical links are in order and
that the fault is a vacuum supply. to confirm this, connect the Vs4021 to the vacuum supply line and check the gauge reading. no vacuum should be
noted at idle but when the engine rPM is increased a vacuum increase should be observed. If this does not occur, trace the vacuum line back checking for
restrictions and breaks.
5.1.
Testing Mechanical fuel pumps
5.1.1. the Vs4021 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 Vs4021 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.
5.2.
carburettors
5.2.1. there are many different types of vacuum control systems used on carburettors. Using the Vs4021 vacuum tester kit allows quick and accurate testing of
these systems. listed below are just two examples of tests that can be carried out:
5.2.2. 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 Vs4021 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.
5.2.3. 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 Vs4021 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.
5.3.
Testing fuel Injection pressure Regulator
5.3.1. 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.
5.3.2. 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 Vs4021 vacuum pump (fig.5) to simulate vacuum pressures in accordance
with the manufacturer’s specifications and note variation in fuel pressure reading.
5.4.
Testing emission control exhaust Gas Reclrculation Valves (eGR)
5.4.1. start engine and run at idle until normal operating temperature is reached. remove the vacuum line from the EGr valve and attach the Vs4021 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.
Original Language Version
© Jack sealey limited
fig.2
fig.3
fig.4
5. fuel sysTeMs
fig.5
fig.6
Vs4021 Issue: 1 - 08/06/12
