1991 OPEL ASTRA Electronic Workshop Manual

Downloaded from www.Manualslib.com manuals search engine 7.9.2 Engine operating conditions.
The following engine operating conditions require additional
modifications to the base injection map.
7.9.3 Intake air temperature.
The oxygen content of the intake air is proportional to the
air density and inversely proportional to the air tempera-
ture. It is therefore necessary to correct the base map for
intake air temperature variations. An air intake tempera-
ture correction factor which is normalised with respect to
303.7øK is therefore used.
7.9.4 Engine temperature.
Cold engines exhibit more friction and therefore require
slightly richer A/F ratios to ensure smooth running. Cor-
rections are made for engine temperatures from -13øC to
110øC and normalised with respect to 100øC.
Cold intake manifolds result in considerable wall-wetting
which means that all the injected fuel does not atomise to
form a combustionable mixture. Additional fuel has to be
injected to overcome this effect.

Downloaded from www.Manualslib.com manuals search engine 7.9.5 Cold starting conditions.
Definition: Engine speed < 450 r.p.m.
During cold start conditions the low inlet manifold tempera-
tures cause considerable fuel condensation on the inner
walls of the manifold. This condition is known as wall
wetting. To ensure correct A/F ratios it is necessary to
increase the quantity of fuel injected during cold starting
conditions to counteract wall wetting. A correction factor
is applied to the base map for engine temperatures between
-40øC and 100øC.
To prevent the engine from flooding the enrichment factor is
not only engine temperature dependent, but also time depend-
ent. This is implemented by reducing the enrichment factor
over a number of crankshaft revolutions, regardless of
engine temperature. If the ignition is turned off and an
attempt is made to re-start the engine the process is re-
peated.
7.9.6 Post start and warm-up conditions.
Definition: Engine speed > 450 r.p.m.
Engine temperature < 80øC
During these conditions the engine temperature is monitored
and the A/F ratio is decreased by lengthening the base map
injection duration to ensure smooth running of the engine
and to compensate for inlet manifold wall-wetting.

Downloaded from www.Manualslib.com manuals search engine 7.9.7 Acceleration conditions.
During a sudden increase in throttle opening at constant
engine speed the air mass entering the manifold and combus-
tion chamber increases almost immediately due to the low
density of air, whilst the higher density fuel lags behind.
This leads to lean mixtures for a short duration if no
compensation is applied. This effect manifests itself as a
hesitation, at the onset of vehicle acceleration.
To compensate for this effect a pre-determined rate of
throttle opening is detected and the effective injection
duration is increased. This enrichment will be gradually
decreased over a number of crankshaft revolutions.
7.9.8 Deceleration lean-out conditions
While driving with the throttle in the part load region a
slight reduction in power demand (throttle opening being
reduced) will result in a momentary enrichment of the A/F
ratio. The ECU prevents this decrease in A/F by making the
injection time shorter for a limited period when detecting
the above conditions.
7.9.9 Coasting conditions.
When the throttle is closed and the engine speed is above
the coasting cut-out speed the ECU will shut the fuel supply
off to save fuel. The engine speed at which fuel is cut
off is temperature dependent to prevent engine stalling
under cold conditions.

Downloaded from www.Manualslib.com manuals search engine 7.9.10 Flooded engine conditions.
When the engine speed is below 450 r.p.m. and WOT is de-
tected the ECU will reduce the base map injection durations
by 40% and ignore all cold and post-start corrections in an
attempt to prevent further flooding.
7.9.11 Full load operation
Under full load operation the engine is required to deliver
maximum power and requires a richer A/F ratio. This condi-
tion is detected when the engine speed is above 450 r.p.m.
and WOT is selected allowing the ECU to increase the base
map injection duration by a given factor to ensure maximum
power delivery.

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 9 IMMOBILISER OPERATION
The system contains an immobiliser function which prevents
hot-wiring. When the ignition is switched on the ECU will
wake up and prompt the ACU for its ID (Identification Code).
The ACU will respond by sending its ID to the ECU for com-
parison with an ID code stored in the ECU's ROM. Only if the
ACU's ID matches the ECU's ID normal engine
management
control will be allowed to take place.NO ENGINE CONTROL IS POSSIBLE IN THE ABSENCE OFTHE CORRECTACU ID.

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

Downloaded from www.Manualslib.com manuals search engine 11 DIAGNOSTICS
Various possible methods of fault finding are listed below
to reduce down-time of the vehicle.
11.1 Diagnostic codes
The CPU continuously monitors its own activities and sensor
inputs. If a fault is detected during operation the diagnos-
tic lamp is turned on and a default signal value is used to
allow the car to be driven with slightly reduced perform-
ance. The fault code is stored in RAM for later evaluation
by the Dealer. If the fault disappears the unit will immedi-
ately use the sensor data instead of the default data, thus
ensuring optimum performance. The fault will be erased from
RAM after 7 starts (ignition turned on 7 times) during which
no fault was detected.
The fault stored in RAM could be accessed by grounding the
diagnostic initialisation input terminal. The fault will
then be flashed out by the diagnostic lamp.