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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 fu nction 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
t
he
base of the
distributor.
The w
eights
move
outwards
advancing
ignition timing
as engine RPM
increases.
This
is
tested
by
firstly
removing the
vacuum advance
line to
disable the
system, then
w
ith
a
timing
light
connected,
run
the engine
RPM
up
checking that
the
!Jrr ng
advaoces 1n accordance
with
the
manufacturer's specification.
4.3.3.
The second method
is
Vacuum
Advance, which
senses
engine
load via
manifold
vacuum.
A vacuum
d iaphragm
is
mounted
onto the
distnl)lllor
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
oper2ting, re move
the
vacuum line
from
the
distributor
advance mechanism. Connect
the VS 402.V2 (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
diaph
ragm
and
mechanical
l
i
nk~
are
in
order and
that the fault
is
a
vacuum
supply.
To
confirm
this,
connect the
VS402.
•12
tc the
vacuum
supply
line
and
check
the g
auge
reading. No
vacuum should
be
noted
at
idle but
when
the engine RPM
is
increased
a
vacuum
increase
should
be
observed. If
this d oe::; not
occur,
1race the
va~uPm
i<ne
back <:ht.
king
for
restrictions
and breaks.
--
-...
(fig.3
lj
/
5.\
FUEL SYSTEMS
5.1.
Testing Mechanical Fuel
Pumps
5.1.1.
The VS402.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 VS402.V2
vacuum
tester to the
suction
port
of
the
pump,
start and run
the engine at
idle.
The
vacuum
reading
that
should
be observed
wHI
vary
slightly on
different makes and
models
but as a general
rule
approximately
15inHg
of
vacuum should be
created.
Th
is
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 pul'np requires either overhaul or replacement.
5.2.
Carburettors
'~
~
5.2.1. There
are many
different
types c;>f vacuum control systems used on carburettors. Using the VS402.V2 vacuum tester kit
allows
quick and accurate
testing
of
these systems.
L
isted 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 VS402.V2
vacuum
tester (fig.3) and apply approximately 15inHg
of vacuum
and wait
for 30 seconds. No
d
rop
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
Barret
Wrth
the
engine
at
normal operating temperature but
not
running,
remove
the
vacuum
line from
the
secondary diaphragm
module.
Connect
the VS402.V2
vacuum tester
{fig.4
),
hold
the throttle
and secondary air
valve
fla
ps
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.
S imply remove and block
off the
vacuum
supply
line to the pressure regulator, connect and operate the VS402.V2
vacuum pump
(fig.5)
to simulate va
cuum
pressures
in
accordance
with the manufacturer's specifications
and
note variation
in
fuel pressure
reading.
5.4.
Testing
Emission
Control
Exhaust
Gas Recirculation
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
a
nd
attach
the
VS402.V2
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.
(
© Jack
Sealey
Limited
Original Language Version
I
VS402.V2
I
Issue:
1
•
22/05/1
2 )
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