Fuel,
Emission and Exhaust System
D.04.09
is
open 80 percent of the time and closed 20
percent of the
time
during one cycle of operation.
(Fig. 28)
To operate the frequency valve at a pulse ratio of
80 20, the ECU module will allow current to flow
through the frequency valve for 80 percent of one
cycle and stop the current flow for the remaining
20 percent of the cycle. When current is flowing
in
the frequency valve, the electromagnet will
energise and open the valve. (Fig. 29)
When the frequency valve
is
open, fuel from the
lower chambers of the fuel distributor
is
released
and routed back to the fuel tank. For example,
if
the exhaust gases reflect a lean condition, the
oxygen sensor
will
signal the ECU module to
change to a pulse ratio that will allow the
frequency valve to remain open for a longer period.
Therefore, an increased amount of fuel
is
fed from
the lower chambers. This reduction of pressure in
the lower chambers causes the diaphragm
in
the
fuel distributor to deflect, injecting more
fue) v??o
the engine; the fuel mixture is now
enriched
The
oxygen sensor will then sense the enriched mixture
and signal the ECU module to switch the
frequency valve back to a shorter pulse ratio that
will reduce the amount of fuel
injecteo.
This
process repeats constantly to maintain the "ideal"
air-fuel mixture ratio. (Fig. 30)
CLOSED
OPEN
Pulse
80/20
80%
20°;
Plr-,a Di ,I^Q
Pi/
D
Fig.
28
J
Fig. 29
CLOSED
OPEN
Pulse
Ratin
60 40
60% 40%
.
One Pulse Cycle
i
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