Opel Frontera UBS. Service 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.
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