Daewoo Nubira. Manual - part 121

1F – 368

I

ENGINE CONTROLS

DAEWOO V–121 BL4

Step

No

Yes

Value(s)

Action

11

Replace any restricted or leaking fuel injectors.
Is the repair complete?

System OK

12

Check the fuel system pressure after a cold start or
during moderate or full throttle acceleration.
Is the fuel pressure within specifications?

41–47 psi

(284–325 kPa)

Go toStep 14

Go toStep 13

13

Repair the restriction in the fuel system or replace
the faulty fuel pump.
Is the repair complete?

System OK

14

1.  Check for faulty ignition wires.
2.  Inspect for fouled spark plugs.
3.  Check the ignition system output on each cylin-

der with a spark tester.

Is the problem found?

Go toStep 15

Go toStep 16

15

Repair or replace any ignition components as need-
ed.
Is the repair complete?

System OK

16

1.  Check the generator output voltage.
2.  Repair or replace the generator if the generator

output is less than the value specified.

3.  Check the Exhaust Gas Recirculation (EGR)

valve operation.

Are all checks and needed repairs complete?

12–16 v

System OK

 

CUTS OUT, MISSES

This Involves a steady pulsation or jerking that
follows engine speed, usually more pronounced as
engine load increases. The exhaust has a steady
spitting sound at idle or low speed.

Step

Action

Value(s)

Yes

No

1

Were the Important Preliminary Checks performed?

Go toStep 2

Go to”Impor-

tant Preliminary

Checks”

2

Check the ignition system output voltage for all of the
cylinders using a spark tester.
Is spark present on all of the cylinders?

Go toStep 3

Go to”Ignition

System Check”

3

1.  Inspect the spark plugs for excessive wear,

insulation cracks, improper gap, or heavy de-
posits.

2.  Check the resistance of the ignition wires. Re-

place any ignition wires that have a resistance
greater than the value specified.

Is the problem found?

30,000 

Ω

Go toStep 4

Go toStep 5

4

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

System OK

5

With the engine running, spray the ignition wires with
a fine water mist to check for arcing and shorting to
ground.
Is the problem found?

Go toStep 6

Go toStep 7

6

Replace the ignition wires.
Is the repair complete?

System OK

ENGINE CONTROLS  1F – 369

DAEWOO V–121 BL4

Step

No

Yes

Value(s)

Action

7

1.  Perform a cylinder compression test.
2.  If the compression is low, repair the engine as

needed.

3.  Inspect for proper valve timing, bent pushrods,

worn rocker arms, broken or weak valve
springs, and worn camshaft lobes.

4.  Inspect the intake manifold and the exhaust

manifold passages for casting flash.

Is the problem found?

Go toStep 8

Go toStep 9

8

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

System OK

9

1.  Check the fuel system for a plugged in–line fuel

filter.

2.  Check the fuel system for low fuel pressure. If

the fuel pressure is below the value specified,
service the fuel system as needed.

3.  Inspect for contaminated fuel.

Is the problem found?

41–47 psi

(284–325 kPa)

Go toStep 10

Go toStep 11

10

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

System OK

11

1.  Disconnect all of the fuel injector harness con-

nectors at the fuel injectors.

2.  Connect an injector test light to the harness

terminals of each fuel injector connector.

3.  Note the test light while cranking the engine for

each fuel injector.

Does the test light blink for all of the fuel injectors?

Go toStep 13

Go toStep 12

12

1.  Repair or replace the faulty injector drive circuit

harness, the connector, or the connector termi-
nal.

2.  If the harness, the connectors, and the termi-

nals are OK, replace the powertrain control
module (PCM)/engine control module (ECM).

Is the repair complete?

System OK

13

Measure the resistance of each fuel injector. The re-
sistance will increase slightly at higher tempera-
tures.
Is the injector resistance within the value specified?

11.6–12.4 

Ω

Go toStep 15

Go toStep 14

14

Replace any fuel injectors with a resistance that is
out of specifications.
Is the repair complete?

System OK

15

Perform an injector balance test.
Is the problem found?

Go toStep 16

Go toStep 17

16

Replace any restricted or leaking fuel injectors.
Is the repair complete?

System OK

1F – 370

I

ENGINE CONTROLS

DAEWOO V–121 BL4

Step

No

Yes

Value(s)

Action

17

1.  Check for electromagnetic interference.
2.  Monitor the engine rpm with a scan tool.

Does the scan tool rpm change greatly with little
change in actual engine rpm?

Go toStep 18

18

1.  Inspect the routing of the ignition wires.
2.  Inspect all of the ignition system grounds.
3.  Correct the routing or repair the ground con-

nections as needed.

Are all checks and needed repairs complete?

System OK

 

POOR FUEL ECONOMY

Fuel economy, as measured by an actual road test, is
noticeably lower than expected. Also, fuel economy
is noticeably lower than it was on this vehicle at one
time, as previously shown by an actual road test.

Important : Driving habits affect fuel economy. Check the
owner’s driving habits by asking the following questions:

1.  Is the A/C system (i.e. defroster mode) turned on

all the time?

2.  Are the tires at the correct air pressure?
3.  Have excessively heavy loads been carried?
4.  Does the driver accelerate too much and too often?

Suggest the driver read the section in the owner’s
manual about fuel economy.

Step

Action

Value(s)

Yes

No

1

Were the Important Preliminary Checks performed?

Go toStep 2

Go to”Impor-

tant Preliminary

Checks”

2

1.  Inspect the air filter for excessive contamina-

tion.

2.  Inspect for fuel system leaks.

Are all needed checks complete?

Go toStep 3

3

1.  Inspect the spark plugs for excessive wear,

insulation cracks, improper gap, or heavy de-
posits.

2.  Replace any faulty spark plugs.
3.  Inspect the ignition wires for cracking, hard-

ness, and proper connections.

Are all needed checks and repairs complete?

Go toStep 4

4

1.  Inspect the engine coolant level.
2.  Check the thermostat for being always open or

for an incorrect heat range.

3.  Replace the thermostat as needed.

Are all needed checks and repairs complete?

Go toStep 5

5

1.  Check the transaxle shift pattern. Ensure all

transaxle gears are functioning.

2.  Check the Torque Converter Clutch (TCC) op-

eration with a scan tool. The scan tool should
indicate rpm drop when the TCC is command-
ed on.

3.  Check for proper calibration of the speedome-

ter.

4.  Check the brakes for dragging.
5.  Check the cylinder compression.
6.  Repair, replace, or adjust any components as

needed.

Are all checks and needed repairs complete?

System OK

 

ENGINE CONTROLS  1F – 371

DAEWOO V–121 BL4

ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING

The engine runs unevenly at idle. If the condition is
bad enough, the vehicle may shake. Also, the idle
varies in rpm (called ”hunting”). Either condition may
be severe enough to cause stalling. The engine idles
at incorrect idle speed.

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

Step

Action

Value(s)

Yes

No

1

Were the Important Preliminary Checks performed?

Go toStep 2

Go to”Impor-

tant Preliminary

Checks”

2

1.  Connect the scan tool to the Data Link Con-

nector (DLC).

2.  Monitor the Oxygen Sensor (O2S) reading at

different throttle positions.

Does the O2S sensor change quickly from rich to
lean at the different throttle positions?

Go toStep 5

Go toStep 3

3

Check the O2S sensor for contamination from fuel
or improper use of Room Temperature Vulcanizing
(RTV) sealant.
Is the O2S sensor contaminated?

Go toStep 4

Go toStep 5

4

Replace the contaminated O2S sensor as needed.
Is the repair complete?

System OK

5

1.  Check for a sticking throttle shaft or binding

throttle linkage that may cause incorrect
Throttle Position (TP) sensor voltage.

2.  Check the TP sensor voltage reading with the

throttle closed.

Is the TP sensor voltage within the value specified?

0.4–0.8 v

Go toStep 6

Go to”Diagnos-

tic Aids for

DTC P0123”

6

1.  Check the Engine Coolant Temperature (ECT)

sensor voltage reading using the scan tool.

2.  Compare the ECT reading with the ambient

temperature when the engine is cold.

Does the ECT temperature reading differ from the
ambient temperature by more than the value speci-
fied?

5

³

F (3

³

C)

Go toStep 7

Go toStep 9

7

Check for high resistance in the ECT sensor circuit
or the sensor itself.
Is the problem found?

Go toStep 8

Go toStep 9

8

Replace the ECT sensor or repair the circuit as
needed.
Is the repair complete?

System OK

9

Check the Manifold Absolute Pressure (MAP) sen-
sor for response and accuracy.
Is the problem found?

Go toStep 10

Go toStep 11

10

Replace the MAP sensor or repair the MAP sensor
circuit as needed.
Is the repair complete?

System OK