17B
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29
PETROL INJECTION
Richness regulation
L90, and K7J, and 710 – L90, and K7M, and 710
17B
I -SENSOR HEATING
The sensors are heated by the computer:
- when the engine is started for the upstream sensor,
- after the engine has been running for a certain length
of time, mapped according to the top dead centre and
the coolant temperature outside the no load position
for the downstream sensor.
The lambda sensors are heated constantly until the en-
gine is switched off.
II - UPSTREAM SENSOR VOLTAGE
Reading on the fault finding tool: parameter "PR009:
UPSTREAM OXYGEN SENSOR VOLTAGE": the va-
lue read represents the voltage supplied to the compu-
ter by the lambda sensor located upstream of the
catalytic converter. It is expressed in mV.
When the engine is operating in a closed loop, the vol-
tage must vary rapidly between two values:
- 20 mV
±±±±
50 for a lean mixture,
- 840 mV
±±±±
70 for a rich mixture.
The smaller the difference is between the minimum and
maximum values, the poorer the signal is from the sen-
sor (this difference is usually 500 mV).
III - DOWNSTREAM SENSOR VOLTAGE
Reading on the fault finding tool: parameter PR010:
DOWNSTREAM LAMBDA SENSOR VOLTAGE: the
value read represents the voltage supplied to the com-
puter by the lambda sensor located downstream from
the catalytic converter. It is expressed in mV.
The function of this sensor is to run diagnostics on the
catalytic converter and to perform a second, more pre-
cise, check on the richness (slow regulation loop). This
function only starts operating after the engine has been
running at normal operating temperature for a while
and does not operate at idle speed.
When the engine is operating in a closed loop, at stabi-
lised speed, the voltage should vary within the range
600 mV
±±±±
100. When decelerating, the voltage should
be less than 200 mV.
The voltage read on the control unit at idling speed
should be ignored.
IV - RICHNESS CORRECTION
The value read on the fault finding tool for parameter
"PR035: RICHNESS CORRECTION VALUE" repre-
sents the average of the richness corrections applied
by the computer depending on the richness of the fuel
mixture as determined by the oxygen sensor located
upstream of the catalytic converter (the oxygen sensor
in fact analyses the oxygen content of the exhaust fu-
mes.
The correction value has an average of 128 and for li-
mits 0 and 255:
- value less than 128: leaner mixture required,
- value greater than 128: richer mixture required.
V - ENTRY INTO RICHNESS REGULATION MODE
Entering the regulation phase takes effect after a timed
starting period if the coolant temperature is more than
22 ˚C and according to a timed period of 28 s after star-
ting the engine.
When the richness regulation phase has not yet been
entered, the value displayed is 128.
Non-loop mode
When richness regulation is occurring, the operating
phases when the computer ignores the voltage infor-
mation from the oxygen sensor are:
- at full load: variable and greater than 128,
- in strong acceleration: variable and greater than 128,
- in deceleration with the no load signal (injection cut-
out): 128,
- in the event of an oxygen sensor fault: 128.
VI - DEFECT MODE IN THE EVENT OF AN OXYGEN
SENSOR FAULT
When the voltage delivered by the lambda sensor is in-
correct (varying very little or not at all) in richness regu-
lation, the computer goes into defect mode (value =
128) if the fault has been recognised as present for 10
seconds. Only in that case will the fault be memorised.
If an oxygen sensor fault is present and recognised and
if the fault has already been stored, the system enters
the open loop mode directly. In this case, the PR035
"Richness correction value" parameter adopts the
value 128.
