1991 OPEL ASTRA Spark

Downloaded from www.Manualslib.com manuals search engine 6.6 Dwell time calculation
Dwell time is the time during which the battery voltage must
be applied to the ignition coil's primary winding prior to
an ignition pulse. The correct dwell time is important to
ensure constant spark energy.
The correct dwell time depends on the battery voltage. A
look-up matrix contains dwell time versus battery voltage.
The prevailing battery voltage is measured and compared with
the voltages stored in the dwell look-up matrix. The corre-
sponding dwell time is used to energise the ignition coil.
6.7 Engine water temperature measurement
EWT measurement is accomplished by a NTC (Negative
Temperature Coefficient) sensor mounted on the engine block.
The base advance angles are increased with decreasing
engine temperatures. This is necessary because it takes
longer to reach maximum cylinder pressure after ignition
when an engine is cold. Typical additional advance required
for an engine at -20ø Celsius ranges from 3ø to 8ø with
respect to an engine operating at 100ø Celsius.

Downloaded from www.Manualslib.com manuals search engine 8 IDLE SPEED CONTROL
Idle speed is controlled by means of the IACV (Idle Air
Control Valve) mounted on the throttle body assembly. The
IACV is driven by the IACSM (Idle Air Control Stepper Motor)
which is controlled by the ECU.
The IACV maintains constant idle speed (temperature depend-
ent) under all engine loads.
The ECU makes use of closed loop control algorithms to
ensure the best idle conditions for warm and cold engines.
Whenever the ignition is first switched the ECU selects a
pre-set idle position which is temperature dependent, there-
after it operates in the closed loop control mode.
Idle speed control is only possible with the throttle in the
closed position.
Timing advance support is utilised in the idle range to
enhance idle speed control. Spark timing is advanced by up
to 10ø if the idle speed drops below the set point, result-
ing in increased engine torque to offset the drop in speed.
If the idle speed rises above the set point the timing will
be retarded up to 10ø to reduce engine torque.
Correct idle speed control is not possible when the battery
voltage is below 9 volt.

Downloaded from www.Manualslib.com manuals search engine 10 DEFAULT MODE SELECTION
When the ECU detects a faulty signal from one of its sensors
it will substitute a default signal value to enable the
vehicle to be driven with degraded performance (see para-
graph 10.1).
Faulty sensor Substitute value/sensor
_____________________________________________________
______
EWT Warm engine - 100 øC
MAT 31 øC
Fuel map selector Zero percent enrichment
Timing map selector Map T1 - RON 87D
TPS Idle speed - 1,000 to
2,000 r.p.m.
MAP TPS and idle speed -
1,000 to 2,000 r.p.m.
Disable distributor
bypass operation and
fix spark timing at
10ø BTDC
CO potentiometer Zero percent