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5. OpERATION
the use of a vacuum gauge is often overlooked when determining mechanical condition and carrying out fault diagnosis on internal combustion
engines. Monitoring actual manifold vacuum is invaluable when troubleshooting engine faults. This can only be carried out by using a good quality
vacuum gauge and this, coupled with a hand-operated vacuum pump, also allows static testing of all types of vacuum operated systems. Set out on
the following pages are applications that the VS4022 vacuum tester kit can be used for, but it must always be remembered that these are examples
only and reference to manufacturer's service manuals should always be made for correct testing procedures and specifications. In addition to this, it
is always recommended that additional tests, ie. compression tests, cylinder leakage tests, ignition timing checks etc. be carried out to confirm
indications of vacuum gauge readings.
5.1.
ANALYSING ENGINE MECHANICAL CONDITION VIA MANIFOLD READINGS
5.1.1.
The readings shown below are only examples of what may be observed.
It is important to remember that it is the action of the needle rather than the
actual reading that is more important. Varying engine types will run different
manifold vacuum pressures, depending on camshaft profile, valve overlap,
timing etc. so an exact vacuum reading cannot be specified. The main
criteria is that the needle reading is between 16 to 21inHg and steady.
5.1.2.
Manifold vacuum is also affected by altitude and it will drop approximately
1inHg for every 1000 feet above sea level so this must also be considered
when assessing manifold vacuum actual readings.
5.2.
BASIC DIAGNOSTIC TESTS
5.2.1.
carry out the following procedures:
5.2.2.
Step 1. run engine until normal operating temperature is reached. switch
engine off.
Step 2. connect the vacuum gauge to a port directly on the manifold (fig.1)
or on the carburettor/throttle body below the throttle butterfly.
Step 3. Start and run the engine at idle, observing the gauge reading.
5.2.3.
Refer to the following diagrams (1 to 9) to indicate any problems and their possible causes.
© Jack sealey limited
Original Language Version
fig.1
VS4022.V2
Issue 1 17/01/18
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