fuel OPEL ASTRA 1991 Electronic Owner's Manual

Downloaded from www.Manualslib.com manuals search engine Volumetric efficiency depends mainly on the:
a) Inlet valve and camshaft design
b) Inlet manifold design
c) Engine speed
The volumetric efficiency is normally less than one (1) and
has the effect that the actual air mass entering the cylin-
der will be less than the measured value.
Peak volumetric efficiency co-insides with the engine speed
where the maximum torque is developed.
7.4 FUEL METERING
Now that a method has been established to determine the air
mass entering the engine it is possible to calculate the
quantity of fuel to be injected to achieve the required A/F
ratio. An electric fuel pump delivers fuel at a constant
pressure to the injector which is opened for the required
injection duration. The fuel pressure is regulated by a
mechanical pressure regulator.
The fuel mass to be injected is:
Fm = Am/(A/F) Where Fm = Fuel mass
Am = Air mass
Since the fuel is injected in bursts it is necessary to know
the fuel flow rate of the injector, pump and regulator
system, as well as the injector opening and closing delays
at various battery voltages to enable calculation of the
injection duration.

Downloaded from www.Manualslib.com manuals search engine 7.5 CONTINUOUS FUEL FLOW RATE
The continuous fuel flow rate at a constant battery voltage
is dependent on the injector design, fuel pump and fuel
pressure used. Tests have shown that the fuel flow rate,
for the Rochester TBi system, is dependent on the applied
battery voltage.
The fuel flow rate becomes lower with reduced battery volt-
age. The ECU compensates for this effect by lengthening the
injection pulses at low battery voltages.
7.6 INJECTOR OPENING AND CLOSING TIME
The current, through the injector coil, creates a magnetic
field which moves the armature, thus opening the nozzle
allowing fuel to be injected. Short opening times therefore
require a fast build up of current in the injector. This
requires a low inductance or a high applied voltage. Short
closing times require a low holding current which is ob-
tained by reducing the opening current while the injector is
open to a current just large enough to keep the injector
open. Since the available voltage in automotive applications
is restricted to the battery voltage (6 to 13.8V) the injec-
tors are normally designed to have low inductance.
The measured characteristics of the test injector are:Inductance = 4mHResistance = 1.5 ohmStatic opening current = 1.1A *Static closing current = 0.5A ** Static opening and closing current is independent of fuelpressure.

Downloaded from www.Manualslib.com manuals search engine The injector drive circuit allows a pull-in current of 4A
and a holding current of 1A. Once an injector current of 4A
is reached the circuit will automatically reduce it to 1A.
Injector opening and closing times vary with battery voltage
and vary between 0.2 ms at 14 volt and 1.35 ms at 6.5 volt.
The ECU takes this into account by measuring the battery
voltage before calculating the injection times.
The electrical opening duration of the injector consists of
the sum of the opening and closing delays and the true
required injection duration.
7.7 INJECTION TIMING
Under static conditions (constant engine load and speed)
fuel will be injected in synchronisation with the crankshaft
position and speed reference signal, i.e. once per intake
stroke. Fuel injection will commence 0.5 ms after the 10ø
BTDC reference.

Downloaded from www.Manualslib.com manuals search engine 7.8 INJECTION DURATION
The base injection duration for different loads and engine
speeds is calculated and fine tuned by mapping to ensure
that the required A/F ratio is obtained under static operat-
ing conditions. (Lambda = 1) Injection durations vary from 1to 5 milliseconds.
The following operating parameters were assumed for the
purpose of obtaining the base map:
a) Continuous fuel flow rates with battery voltage
at 14 volt.
b) Intake air temperature at 303.7 øKelvin.
c) Zero injector delay.
d) One injection cycle per intake stroke.
7.9 CORRECTION FACTORS
Correction factors are applied to the base map to correct
for injection hardware deficiencies and engine operating
conditions.
7.9.1 Injection hardware deficiencies.
The reduced fuel flow rate at low battery voltages necessi-
tates an increase in the injection duration. The factor by
which the injection durations from the base map has to be
multiplied is obtained by normalising the fuel flow rate at
different battery voltages with respect to 14.0 volt.
In addition to the above multiplication factor the base map
injection times are further increased by the injector delays
to ensure that the correct quantity of fuel is injected.

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 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 DIAGNOSTIC CODES
Code Cause
_____________________________________________________
14 Coolant temperature sensor voltage too low
15 Coolant temperature sensor voltage too high
21 TPS voltage too high
22 TPS voltage too low
25 MAT sensor voltage too low
26 MAT sensor voltage too high
33 MAP sensor voltage too high
34 MAP sensor voltage too low
35 Idle control stepper motor failure
36 Timing map selector error
42 Reference signal error/Engine stall
(Diagnostic lamp will not turn ON)
44 Fuel map selector error
48 Battery voltage too low
49 Battery voltage too high
65 CO potentiometer voltage out of range

Downloaded from www.Manualslib.com manuals search engine 11.2.8 Timing map selector: The resistance between terminal
19B and 22B measured on the harness connector with the
ECU removed should be:
97 RON - 470 ohm
93 RON - 220 ohm
87 RON - 4,700 ohm
87D RON - 5,600 ohm
11.2.9 Fuel mixture selector: The resistance between terminal
18B and 11A measured on the harness connector with the
ECU removed should be:
-15% - 274 ohm
-10% - 340 ohm
-05% - 412 ohm
+05% - 619 ohm
+10% - 768 ohm
+15% - 931 ohm
+20% - 1180 ohm
+25% - 1500 ohm