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Daewoo Nubira. Service manual - part 123

1F – 376

ENGINE CONTROLS

DAEWOO V–121 BL4

BACKFIRE

Fuel ignites in the intake manifold, or in the exhaust
system, making a loud popping noise.

Important : Before diagnosing the symptom, check ser-
vice bulletins for updates.

Step

Action

Value(s)

Yes

Were the Important Preliminary Checks performed?

Go toStep 2

Go to”Impor-

tant Preliminary

Checks”

1. Inspect for crossed or crossfiring ignition wires.
2. Check the ignition system output voltage for all

cylinders using a spark tester.

3. Inspect the spark plugs for excessive wear,

burned electrodes, improper gap, or heavy de-
posits..

Is the problem found?

Go toStep 3

Go toStep 4

Repair or replace any ignition system components
as needed.
Is the repair complete?

System OK

1. Check the fuel system operation.
2. Check the fuel injectors by performing an injec-

tor diagnosis.

Is the problem found?

Go toStep 5

Go toStep 6

Repair or replace any fuel system components as
needed.
Is the repair complete?

System OK

1. Inspect the Exhaust Gas Recirculation (EGR)

gasket for a leak or a loose fit.

2. Check the EGR valve for proper operation.
3. Inspect the intake manifold and the exhaust

manifold for a casting flash.

Is the problem found?

Go toStep 7

Go toStep 8

Repair or replace any components as needed.
Is the repair complete?

System OK

1. Inspect the timing belt for proper installation

and tension.

2. Check the engine compression.
3. Inspect the intake manifold gasket and the ex-

haust manifold gasket for leaks.

4. Check for sticking or leaking valves.
5. Repair or replace any components as needed.

Are all checks and corrections complete?

System OK

1F – 404

ENGINE CONTROLS

DAEWOO V–121 BL4

GENERAL DESCRIPTION

AND SYSTEM OPERATION

IGNITION SYSTEM OPERATION

This ignition system does not use a conventional distribu-
tor and coil. It uses a crankshaft position sensor input to
the powertrain control module (PCM)/engine control mod-
ule (ECM). The PCM/ECM then determines Electronic
Spark Timing (EST) and triggers the direct ignition system
ignition coil.

This type of distributorless ignition system uses a ”waste
spark” method of spark distribution. Each cylinder is
paired with the cylinder that is opposite it (1–4 or 2–3). The
spark occurs simultaneously in the cylinder coming up on
the compression stroke and in the cylinder coming up on
the exhaust stroke. The cylinder on the exhaust stroke re-
quires very little of the available energy to fire the spark
plug. The remaining energy is available to the spark plug
in the cylinder on the compression stroke.

These systems use the EST signal from the PCM/ECM to
control the electronic spark timing. The PCM/ECM uses
the following information:

Engine load (manifold pressure or vacuum).

Atmospheric (barometric) pressure.

Engine

temperature.

Intake air temperature.

Crankshaft

position.

Engine speed (rpm).

ELECTRONIC IGNITION SYSTEM
IGNITION COIL

The Electronic Ignition (EI) system ignition coil provides
the spark for two spark plugs simultaneously. The EI sys-
tem ignition coil is not serviceable and must be replaced
as an assembly.

CRANKSHAFT POSITION SENSOR

This direct ignition system uses a magnetic crankshaft
position sensor. This sensor protrudes through its mount
to within approximately 0.05 inch (1.3 mm) of the crank-
shaft reluctor. The reluctor is a special wheel attached to
the crankshaft or crankshaft pulley with 58 slots machined
into it, 57 of which are equally spaced in 6 degree intervals.
The last slot is wider and serves to generate a ”sync
pulse.” As the crankshaft rotates, the slots in the reluctor
change the magnetic field of the sensor, creating an in-
duced voltage pulse. The longer pulse of the 58th slot
identifies a specific orientation of the crankshaft and al-
lows the powertrain control module (PCM)/engine control
module (ECM) to determine the crankshaft orientation at
all times. The PCM/ECM uses this information to generate
timed ignition and injection pulses that it sends to the igni-
tion coils and to the fuel injectors.

CAMSHAFT POSITION SENSOR

The Camshaft Position (CMP) sensor sends a CMP sen-
sor signal to the powertrain control module (PCM)/engine
control module (ECM). The PCM/ECM uses this signal as
a ”sync pulse” to trigger the injectors in the proper se-
quence. The PCM/ECM uses the CMP sensor signal to in-
dicate the position of the #1 piston during its power stroke.
This allows the PCM/ECM to calculate true sequential fuel
injection mode of operation. If the PCM/ECM detects an
incorrect CMP sensor signal while the engine is running,
DTC P0341 will set. If the CMP sensor signal is lost while
the engine is running, the fuel injection system will shift to
a calculated sequential fuel injection mode based on the
last fuel injection pulse, and the engine will continue to run.
As long as the fault is present, the engine can be restarted.
It will run in the calculated sequential mode with a 1–in–6
chance of the injector sequence being correct.

IDLE AIR SYSTEM OPERATION

The idle air system operation is controlled by the base idle
setting of the throttle body and the Idle Air Control (IAC)
valve.

The powertrain control module (PCM)/engine control
module (ECM) uses the IAC valve to set the idle speed de-
pendent on conditions. The PCM/ECM uses information
from various inputs, such as coolant temperature, man-
ifold vacuum, etc., for the effective control of the idle
speed.

FUEL CONTROL SYSTEM
OPERATION

The function of the fuel metering system is to deliver the
correct amount of fuel to the engine under all operating
conditions. The fuel is delivered to the engine by the indi-
vidual fuel injectors mounted into the intake manifold near
each cylinder.

The two main fuel control sensors are the manifold abso-
lute pressure (MAP) sensor and the oxygen sensor O2S
1).

The MAP sensor measures or senses the intake manifold
vacuum. Under high fuel demands the MAP sensor reads
a low vacuum condition, such as wide open throttle. The
powertrain control module (PCM)/engine control module
(ECM) uses this information to richen the mixture, thus in-
creasing the fuel injector on–time, to provide the correct
amount of fuel. When decelerating, the vacuum in-
creases. This vacuum change is sensed by the MAP sen-
sor and read by the PCM/ECM, which then decreases the
fuel injector on–time due to the low fuel demand condi-
tions.

The O2S sensor is located in the exhaust manifold. The
O2S sensor indicates to the PCM/ECM the amount of oxy-
gen in the exhaust gas and the PCM/ECM changes the air/
fuel ratio to the engine by controlling the fuel injectors. The
best air/fuel ratio to minimize exhaust emissions is 14.7 to
1, which allows the catalytic converter to operate most effi-

ENGINE CONTROLS 1F – 405

DAEWOO V–121 BL4

ciently. Because of the constant measuring and adjusting
of the air/fuel ratio, the fuel injection system is called a
”closed loop” system.

The PCM/ECM uses voltage inputs from several sensors
to determine how much fuel to provide to the engine. The
fuel is delivered under one of several conditions, called
”modes.”

Starting Mode

When the ignition is turned ON, the PCM/ECM turns the
fuel pump relay on for two seconds. The fuel pump then
builds fuel pressure. The PCM/ECM also checks the En-
gine Coolant Temperature (ECT) sensor and the Throttle
Position (TP) sensor and determines the proper air/fuel ra-
tio for starting the engine. This ranges from 1.5 to 1 at
–97

F (–36

C) coolant temperature to 14.7 to 1 at 201

(94

C) coolant temperature. The PCM/ECM controls the

amount of fuel delivered in the starting mode by changing
how long the fuel injector is turned on and off. This is done
by ”pulsing” the fuel injectors for very short times.

Clear Flood Mode

If the engine floods with excessive fuel, it may be cleared
by pushing the accelerator pedal down all the way. The
PCM/ECM will then completely turn off the fuel by eliminat-
ing any fuel injector signal. The PCM/ECM holds this injec-
tor rate as long as the throttle stays wide open and the en-
gine is below approximately 400. If the throttle position
becomes less than approximately 80 percent, the PCM/
ECM returns to the starting mode.

Run Mode

The run mode has two conditions called ”open loop” and
”closed loop.”

Open Loop

When the engine is first started and it is above 400 rpm,
the system goes into ”open loop” operation. In ”open loop,”
the PCM/ECM ignores the signal from the O2S and calcu-
lates the air/fuel ratio based on inputs from the ECT sensor
and the MAP sensor. The sensor stays in ”open loop” until
the following conditions are met:

The O2S sensor has a varying voltage output,
showing that it is hot enough to operate properly.

The ECT sensor is above a specified temperature.

A specific amount of time has elapsed after starting
the engine.

Closed Loop

The specific values for the above conditions vary with dif-
ferent engines and are stored in the Electronically Eras-
able Programmable Read–Only Memory (EEPROM).
When these conditions are met, the system goes into
”closed loop” operation. In ”closed loop,” the PCM/ECM
calculates the air/fuel ratio (fuel injector ontime) based on
the signal from the oxygen sensor. This allows the air/fuel
ratio to stay very close to 14.7 to 1.

Acceleration Mode

The PCM/ECM responds to rapid changes in throttle posi-
tion and airflow and provides extra fuel.

Deceleration Mode

The PCM/ECM responds to changes in throttle position
and airflow and reduces the amount of fuel. When decel-
eration is very fast, the PCM/ECM can cut off fuel com-
pletely for short periods of time.

Battery Voltage Correction Mode

When battery voltage is low, the PCM/ECM can compen-
sate for a weak spark delivered by the ignition module by
using the following methods:

Increasing the fuel injector pulse width.

Increasing the idle speed rpm.

Increasing the ignition dwell time.

Fuel Cut–Off Mode

No fuel is delivered by the fuel injectors when the ignition
is OFF. This prevents dieseling or engine run–on. Also, the
fuel is not delivered if there are no reference pulses re-
ceived from the central power supply. This prevents flood-
ing.

EVAPORATIVE EMISSION CONTROL
SYSTEM OPERATION

The basic Evaporative (EVAP) Emission control system
used is the charcoal canister storage method. This meth-
od transfers fuel vapor from the fuel tank to an activated
carbon (charcoal) storage device (canister) to hold the va-
pors when the vehicle is not operating. When the engine
is running, the fuel vapor is purged from the carbon ele-
ment by intake airflow and consumed in the normal com-
bustion process.

Gasoline vapors from the fuel tank flow into the tube la-
beled TANK. These vapors are absorbed into the carbon.
The canister is purged by the powertrain control module
(PCM)/engine control module (ECM) when the engine has
been running for a specified amount of time. Air is drawn
into the canister and mixed with the vapor. This mixture is
then drawn into the intake manifold.

The PCM/ECM supplies a ground to energize the EVAP
emission canister purge solenoid valve. This valve is Pul-
seWidth Modulated (PWM) or turned on and off several
times a second. The EVAP emission canister purge PWM
duty cycle varies according to operating conditions deter-
mined by mass airflow, fuel trim, and intake air tempera-
ture.

Poor idle, stalling, and poor driveability can be caused by
the following conditions:

An inoperative EVAP emission canister purge sole-
noid valve.

A damaged canister.

Hoses that are split, cracked, or not connected to
the proper tubes.

1F – 406

ENGINE CONTROLS

DAEWOO V–121 BL4

EVAPORATIVE EMISSION CANISTER

The Evaporative (EVAP) Emission canister is an emission
control device containing activated charcoal granules.
The EVAP emission canister is used to store fuel vapors
from the fuel tank. Once certain conditions are met, the
powertrain control module (PCM)/engine control module
(ECM) activates the EVAP canister purge solenoid, allow-
ing the fuel vapors to be drawn into the engine cylinders
and burned.

POSITIVE CRANKCASE
VENTILATION CONTROL SYSTEM
OPERATION

A Positive Crankcase Ventilation (PCV) system is used to
provide complete use of the crankcase vapors. Fresh air
from the air cleaner is supplied to the crankcase. The fresh
air is mixed with blowby gases which are then passed
through a vacuum hose into the intake manifold.

Periodically inspect the hoses and the clamps. Replace
any crankcase ventilation components as required.

A restricted or plugged PCV hose may cause the following
conditions:

Rough

idle

Stalling or low idle speed

Oil

leaks

Oil in the air cleaner

Sludge in the engine

A leaking PCV hose may cause the following conditions:

Rough

idle

Stalling

High idle speed

ENGINE COOLANT TEMPERATURE
SENSOR

The Engine Coolant Temperature (ECT) sensor is a
thermistor (a resistor which changes value based on tem-
perature) mounted in the engine coolant stream. Low cool-
ant temperature produces a high resistance (100,000
ohms at –40

F [–40

C]) while high temperature causes

low resistance (70 ohms at 266

F [130

C]).

The powertrain control module (PCM)/engine control
module (ECM) supplies 5 volts to the ECT sensor through
a resistor in the PCM/ECM and measures the change in
voltage. The voltage will be high when the engine is cold,
and low when the engine is hot. By measuring the change
in voltage, the PCM/ECM can determine the coolant tem-
perature. The engine coolant temperature affects most of
the systems that the PCM/ECM controls. A failure in the
ECT sensor circuit should set a diagnostic trouble code
P0117 or P0118. Remember, these diagnostic trouble
codes indicate a failure in the ECT sensor circuit, so prop-
er use of the chart will lead either to repairing a wiring prob-
lem or to replacing the sensor to repair a problem properly.

THROTTLE POSITION SENSOR

The Throttle Position (TP) sensor is a potentiometer con-
nected to the throttle shaft of the throttle body. The TP sen-
sor electrical circuit consists of a 5 volt supply line and a
ground line, both provided by the powertrain control mod-
ule (PCM)/engine control module (ECM). The PCM/ECM
calculates the throttle position by monitoring the voltage
on this signal line. The TP sensor output changes as the
accelerator pedal is moved, changing the throttle valve
angle. At a closed throttle position, the output of the TP
sensor is low, about 0.5 volt. As the throttle valve opens,
the output increases so that, at Wide Open Throttle
(WOT), the output voltage will be about 5 volts.

The PCM/ECM can determine fuel delivery based on
throttle valve angle (driver demand). A broken or loose TP
sensor can cause intermittent bursts of fuel from the injec-
tor and an unstable idle, because the PCM/ECM thinks the
throttle is moving. A problem in any of the TP sensor cir-
cuits should set a diagnostic trouble code (DTC) P0121 or
P0122. Once the DTC is set, the PCM/ECM will substitute
a default value for the TP sensor and some vehicle perfor-
mance will return. A DTC P0121 will cause a high idle
speed.

CATALYST MONITOR OXYGEN
SENSORS

Three–way catalytic converters are used to control emis-
sions of hydrocarbons (HC), carbon monoxide (CO), and
oxides of nitrogen (NOx). The catalyst within the convert-
ers promotes a chemical reaction. This reaction oxidizes
the HC and CO present in the exhaust gas and converts
them into harmless water vapor and carbon dioxide. The
catalyst also reduces NOx by converting it to nitrogen. The
powertrain control module (PCM)/engine control module
(ECM) can monitor this process using the Bank 1 Sensor
1 and Bank 1 Sensor 2 sensors. These sensors produce
an output signal which indicates the amount of oxygen
present in the exhaust gas entering and leaving the three–
way converter. This indicates the catalyst’s ability to effi-
ciently convert exhaust gasses. If the catalyst is operating
efficiently, the Bank 1 Sensor 1 sensor signals will be more
active than the signals produced by the Bank 1 Sensor 2
sensor. The catalyst monitor sensors operate the same
way as the fuel control sensors. The sensor’s main func-
tion is catalyst monitoring, but they also have a limited role
in fuel control. If a sensor output indicates a voltage either
above or below the 450 mv bias voltage for an extended
period of time, the PCM/ECM will make a slight adjust-
ment to fuel trim to ensure that fuel delivery is correct for
catalyst monitoring.

A problem with the Bank 1 Sensor 1 sensor circuit will set
DTC P0131, P0132, P0133 or P0134 depending, on the
special condition. A problem with the Bank 1 Sensor 2 sen-
sor signal will set DTC P0137, P0138, P0140 or P0141,
depending on the special condition.

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