Lotus TURBO ESPRIT Service Manual page 391

The
E.C.U.
sets fixed duty cycles under the following conditiors:
i) 75% duty cycle a t engine o i l temperatures below 3 5 ' ~ as sensed by the
the low temperature switch.
ii)
65% duty cycle on engine overun, when fuel by-pass valve (LD.16)
i s
opera t i ng
.
iii)
65% duty cycle a t throttle butterfly openings of more than
30°,
as
sensed by the throttle position switch.
i v )
65%
duty cycle at engine speeds higher than 3250 rpm as sensed by
'fuel enrichment module' mounted on
R H
fuel tank board.
v)
50% duty cycle i f a defect i n the Lambda sensor
i s
detected (unless
conditions
i, ii, iii
or i v above apply).
a
A t idle speed, the E.C.U. updates the closed loop duty cycle rate more quickly i n
order t o stabilize idle rpm.
LD.
16
-
FUEL
BY-PASS
VALVE
The fuel shut off valve has been incorporated into the fuel system to improve economy
during engine overun by returning the air sensor plate to its rest position, shutting off
the fuel supply. This i s achieved by collapsing the depression below the sensor plate
b y allowing air from the a i r cleaner homing to be fed directly into the a i r ducting
below the plate.
The valve i s controlled by a n electric power supply and manifold vacuum but governed
by the engine coolant temperature, engine speed and the position of the throttle.
The
valve has an a i r inlet and outlet w i t h the inlet spigot pressed into a grommet i n the a i r
cleaner main body while the outlet i s connected by hose to the a i r flow sensor lower
housing. When the valve i s triggered to its open position air w i l l be drawn through the
valve into the lower housing collapsing the vacuum below the plate. The sensor plate
movement w i l l be restored as soon
as
the valve closes.
The following conditions must occur for the valve to be acti\cqted:
The coolant temperature, sensed by the high temperature switch must
be above
7 0 °
C
This i s to ensure that the driveability i s not affected
during engine warm up.
The throttle must be 'closed'.
A
throttle position switch controls this
operation ensuring that the by-pass valve only operates i n the i d l e
position.
The engine must be decelemting from a speed greater than 16d0 rprn
.
Two critical speeds control the valve operation.
It w i l l not be
activated unless the engine
is
deceierating from above
1600
rpm and
.
i t
w i l l cut out once the speed dropsdown to !400cpm. The engine
speeds are monitored by a speed sensing relay, mounted i n the ignition
box at the rear of the engine bay.