Finishing the job
Once a satisfactory synchronisation has been achieved, switch over once again to the RPM function
and reset the engine idling speed as required. Switch off the engine, disconnect the VacuumMate’s
electrical input from the source and from the enclosure, and disconnect the pneumatic engine
connections taking care not to burn your fingers ! The connection adapters and other accessories
are best kept for safe-keeping together with the VacuumMate itself either in the custom travel case
or, if you have a
StandMate
(see page 5), in the compartmentalised steel tray and instrument holder.
8. DIAGNOSTICS : HOW TO USE THE “DYN” DYNAMIC MODE
IMPORTANT: If you have not yet read section 3. “AVE & DYN VACUUM MEASUREMENT
MODES”, please do so before reading the following section.
By monitoring and displaying the DYNAMIC intake vacuum waveform characteristics one can reveal
the existence and nature of engine seal defects which distort & thwart attempts at synchronisation. In
case of difficulty in arriving at a satisfactory synchronisation, even after several attempts, (in which
case you may also have noticed an irregular engine rhythm), select the
DYN
mode (but only after
trying as best you can to synchronise in
AVE
mode).
Some engine seal defects quickly diagnosed in
DYN
mode are Leaking intake or exhaust valves
'False' air entering the intake system
Compression loss….
Background information
The diagrams below show some more realistic examples of pressure waveforms which can occur in
the intake manifold of a 4-stroke engine. Compare with the drawings on page 2.
The pressure scale orientation has been deliberately inverted so as to rather show vacuum scale so
as to correlate with the LED displays of the VacuumMate.
The display appears as a shimmering column of light. In reality a single LED on each connected
display channel follows the wave-form curve (from left to right) at great speed rather like a very fast
roller-coaster car, tracing the vacuum wave-form between troughs and crests. Because the speed of
observation of the human eye cannot match that of the running engine’s vacuum wave-form your eye
sees the resulting display as a column of light of height and position equating to the troughs and
crests.
NORMAL INTAKE
VACUUM WAVE-FORM
– ENGINE SEALS O.K.
The
LED-column
display illustrated with
a typical intake
pressure wave-form
During the intake stroke
the intake valve is open
and the piston moves
down, increasing the
vacuum until the crest of
the vacuum wave-form
(inverted pressure wave-
form) is attained.
When the intake valve closes, suction ceases and the mixture coming through the throttle valve fills
up the vacuum, so that the vacuum is “released” to atmospheric pressure (Pa mark) at the trough of
the vacuum wave-form. The slight apparent “over-shooting” of the Pa mark datum can be thought of
as due to “shock” effect.
7
