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4.3 Ignition system vacuum Advance
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.
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.
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's specifications. In
the event that the vacuum advance is not operating, remove the vacuum
line from the distributor advance mechanism. Connect the VS403.V2
(fig.4) and create a 5-10 inHg 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 VS403.V2 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
or breaks.
fig.4
fig.5
fig.6
4.4 fueL sysTeMs: Testing Mechanical fuel Pumps
The VS403.V2 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 VS403.V2
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 15 inHg
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.
carburettors
There are many different types of vacuum control systems used on
carburettors. Using the VS403.V2 vacuum tester kit allows quick and
accurate testing of these systems. Below are just two examples of tests
that can be carried out.
example 1.
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 VS403.V2 vacuum tester (fig.5) and apply
approximately 15 inHg 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.
example 2.
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 VS403.V2 vacuum
tester (fig.6), hold the throttle and secondary air valve flaps open.
operate the hand pump whilst observing free and easy opening of the
secondary throttle butterfly.
Testing fuel Injection Pressure Regulator
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. 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 VS403.V2 vacuum pump
(fig.7) to simulate vacuum pressures in accordance with the
manufacturer's specifications and note variation in fuel pressure reading.
Testing emission control exhaust Gas Reclrculation
valves (eGR)
Start engine and run at idle until normal operating temperature is
reached. remove the vacuum line from the EGr valve and attach the
VS403.V2 vacuum tester kit (fig.8). operate the hand pump to apply
approximately 15 inHg 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
fig.7
fig.8
VS403.V2
Issue: 1 - 09/01/12
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