NEO TOOLS 11-267 Mode D'emploi page 7

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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 R 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 CT3258 (fig.3) 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 CT3258 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.
4.4. FUEL SYSTEMS: Testing Mechanical Fuel Pumps
The CT3258 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 CT3258 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 this 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 CT3258 (fig.4) 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 CT3258 (fig.5), 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,
All manuals and user guides at all-guides.com
connect and operate the CT3258 vacuum pump (fig.6) 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 CT3258 vacuum
tester kit (fig.7). 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.
4.5. Testing One-Way Valves
Many vacuum operated circuits use in-line one-way valves to apply vacuum
in one direction only. To test the function of the valve remove it from the
circuit. Attach the CT3258 vacuum tester (fig.8) and operate pump to apply
vacuum. In one direction the valve should hold vacuum and in the opposite
direction it should not.
4.6. Testing Electrically Operated Vacuum Solenoids
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
CT3258 is extremely simple. Locate the solenoid to be tested and remove
the line that goes to the component being tested. Connect the CT3258
to the solenoid port (fig.9) 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 or breaks.
4.7. Testing Thermal Vacuum Switches
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.
To test this type of switch, remove the vacuum supply line coming from
the manifold to the switch and test for manifold vacuum. If this vacuum is
correct refit the supply line to the thermal switch and remove the opposing
line from the switch. Attach the CT3258 vacuum tester to the port (fig.10)
and start the engine. With a cold engine no reading should be noted. When
the engine reaches normal operating temperature a manifold vacuum
reading should be seen.
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