Opel Frontera UBS. Manual - part 1181

6E–90

ENGINE DRIVEABILITY AND EMISSIONS

Fuel System Diagnosis

 

Step

Action

Value(s)

Yes

No

1

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to 

Step 2

Go to 

OBD

System

Check

2

1. Turn the ignition “OFF.”
2. Turn the air conditioning system “OFF.”
3. Relieve fuel system pressure and install the fuel

pressure gauge.

4. Turn the ignition “ON.”

NOTE: The fuel pump will run for approximately 2
seconds.  Use Tech 2 to command the fuel pump “ON”.

5. Observe the fuel pressure indicated by the fuel

pressure gauge with the fuel pump running.

Is the fuel pressure within the specified limits?

290-376 kPa

(42-55 psi)

Go to 

Step 3

Go to 

Step 17

3

NOTE: The fuel pressure will drop when the fuel pump
stops running, then it should stabilize and remain
constant.

Does the fuel pressure indicated by the fuel pressure
gauge remain constant?

—

Go to 

Step 4

Go to 

Step 12

4

1. When the vehicle is at normal operation

temperature, turn the ignition “ON” to build fuel
pressure and observe the measurement on the
gauge.

2. Start the engine and observe the fuel pressure

gauge.

Did the reading drop by the amount specified after the
engine was started?

21-105 kPa

(3-15 psi)

Go to 

Step 5

Go to 

Step 9

5

Is fuel pressure dropping off during acceleration,
cruise, or hard cornering?

—

Go to 

Step 6

Check for

improper fuel

6

Visually and physically inspect the following items for a
restriction:

D

The in-pipe fuel filter.

D

The fuel feed line.

Was a restriction found?

—

Verify repair

Go to 

Step 7

7

Remove the fuel tank and visually and physically
inspect the following items:

D

The fuel pump strainer for a restriction.

D

The fuel line for a leak.

D

Verify that the correct fuel pump is in the vehicle.

Was a problem found in any of these areas?

—

Verify repair

Go to 

Step 8

8

Replace the fuel pump.

Is the action complete?

—

Verify repair

—

9

1. Disconnect the vacuum hose from the fuel pressure

regulator.

2. With the engine idling, apply 12-14 inches of

vacuum to the fuel pressure regulator.

Does the fuel pressure indicated by the fuel pressure
gauge drop by the amount specified?

21-105 kPa

(3-15 psi)

Go to 

Step 10

Go to 

Step 11

6E–91

ENGINE DRIVEABILITY AND EMISSIONS

Fuel System Diagnosis

  (Cont'd)

Step

No

Yes

Value(s)

Action

10

Locate and repair the loss of vacuum to the fuel
pressure regulator.

Is the action complete?

—

Verify repair

—

11

Replace the fuel pressure regulator.

Is the action complete?

—

Verify repair

—

12

1. Run the fuel pump with Tech 2.
2. After pressure has built up, turn off the pump and

clamp the supply hose shut with suitable locking
pliers.

Does the fuel pressure indicated by the fuel pressure
gauge remain constant?

—

Go to 

Step 13

Go to 

Step 15

13

Visually inspect the fuel supply line and repair any
leaks.

Was a problem found?

—

Verify repair

Go to 

Step 14

14

Remove the fuel tank and inspect for leaky hose or
in-tank fuel line.

Was a problem found?

—

Verify repair

Go to 

Step 8

15

1. If the pliers are still clamped to the fuel supply hose,

remove the locking pliers.

2. With suitable locking pliers, clamp the fuel return

line to prevent fuel from returning to the fuel tank.

3. Run the fuel pump with Tech 2.
4. After pressure has built up, remove power to the

pump.

Does the fuel pressure indicated by the fuel pressure
gauge remain constant?

—

Go to 

Step 11

Go to 

Step 16

16

Locate and replace any leaking fuel injector(s).

Is the action complete?

—

Verify repair

—

17

Is the fuel pressure indicated by the fuel pressure
gauge above the specified limit?

376 kPa

(55 psi)

Go to 

Step 18

Go to 

Step 21

18

1. Relieve the fuel pressure.  Refer to the 

Fuel

Pressure Relief.

2. Disconnect the fuel return line from the fuel rail.
3. Attach a length of flexible hose to the fuel rail return

outlet passage.

4. Place the open end of the flexible hose into an

approved gasoline container.

5. Run the fuel pump with Tech 2.
6. Observe the fuel pressure indicated by the fuel

pressure gauge with the fuel pump running.

Is the fuel pressure within the specified limits?

290-376 kPa

(42-55 psi)

Go to 

Step 19

Go to 

Step 20

19

Locate and correct the restriction in the fuel return line.

Is the action complete?

—

Verify repair

—

20

Visually and physically inspect the fuel rail outlet
passages for a restriction.

Was a restriction found?

—

Verify repair

Go to 

Step 11

21

Is the fuel pressure indicated by the fuel pressure
gauge above the specified value?

0 kPa (0 psi)

Go to 

Step 22

Go to 

Step 23

6E–92

ENGINE DRIVEABILITY AND EMISSIONS

Fuel System Diagnosis

  (Cont'd)

Step

No

Yes

Value(s)

Action

22

1. Command the fuel pump “ON” with Tech 2.
2. Using suitable pliers which will not damage the fuel

hose, gradually apply pressure with the pliers to
pinch the flexible fuel return hose closed.

CAUTION: Do not let the fuel pressure exceed
the second specified value.

Does the fuel pressure indicated by the fuel pressure
gauge rise above the first specified value?

376 kPa

(55 psi)

414 kPa

(60 psi)

Go to 

Step 11

Go to 

Step 7

23

1. Command the fuel pump “ON” with Tech 2.
2. Remove the fuel filler cap and listen for the sound of

the fuel pump running.

3. Turn the pump off.

Was the fuel pump running?

—

Go to 

Step 7

Go to 

Fuel

System

Electrical Test

Chart

6E–93

ENGINE DRIVEABILITY AND EMISSIONS

Idle Air Control (IAC) System Check

Circuit Description

The powertrain control module (PCM) controls engine
idle speed with the idle air control (IAC) valve.  To increase
idle speed, the PCM retracts the IAC valve pintle away
from its seat, allowing more air to bypass the throttle bore.
To decrease idle speed, it extends the IAC valve pintle
towards its seat, reducing by pass air flow.  Tech 2 will
read the PCM commands to the IAC valve in counts.
Higher counts indicate more air bypass (higher idle).
Lower counts indicate less air is allowed to bypass (lower
idle).

Diagnostic Aids

A slow, unstable, or fast idle may be caused by a non-IAC
system problem that cannot be overcome by the IAC
valve.  Out of control range IAC Tech 2 counts will be
above 60 if idle is too low, and zero counts if idle is too
high.  The following checks should be made to repair a
non-IAC system problem:

D

Vacuum leak (high idle) – If idle is too high, stop the
engine.  Fully extend (low) IAC with the Tech 2.  Start
the engine.  If idle speed is above 800 RPM, locate and
correct the vacuum leak, including the PCV system.
Check for binding of the throttle blade or linkage.

D

Lean heated oxygen sensor signal (high air/fuel ratio) –
The idle speed may be too high or too low.  Engine
speed may vary up and down, and disconnecting the
IAC valve does not help.  Diagnostic trouble codes
P0131, P0151, P0171, or P0174 may be set.  Tech 2
oxygen (O2) voltage will be less than 100 mV (0.1 V).
Check for low regulated fuel pressure, water in fuel, or
a restricted injector.

D

Rich heated oxygen sensor signal (low air/fuel ratio) –
The idle speed will be too low.  Tech 2 IAC counts will
usually be above 80.  The system is obviously rich and
may exhibit black smoke in the exhaust.

Tech 2 O2 voltage will be fixed at about 750 mV (0.75
V).  Check for high fuel pressure, or a leaking or
sticking injector.  A silicon-contaminated heated
oxygen sensor will show an O2 voltage slow to
respond on Tech 2.

D

Throttle body – Remove the IAC valve and inspect the
bore for foreign material.

D

IAC valve electrical connections – IAC valve
connections should be carefully checked for proper
contact.

D

PCV valve – An incorrect or faulty PCV valve may
result in an incorrect idle speed.  Refer to 

Diagnosis,

Rough Idle, Stalling.  If intermittent poor driveability or
idle symptoms are resolved by disconnecting the IAC,
carefully recheck the connections and valve terminal
resistance, or replace the IAC.

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.
1. The Tech 2 is used to extend and retract the IAC

valve.  Valve movement is verified by an engine
speed change.  If no change in engine speed
occurs, the valve can be resettled when removed
from the throttle body.

2. This step checks the quality of the IAC movement in

step 1.  Between 700 revolutions per minute (RPM)
and about 1500 RPM, the engine speed should
change smoothly with each flash of the tester light
in both extend and retract.  If the IAC valve is
retracted beyond the control range (about 1500
RPM), it may take many flashes to extend the IAC
valve before engine speed will begin to drop.  This
is normal on certain engines.  Fully extending the
IAC may cause engine stall.  This may be normal.