Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Manual - part 1416

6E2–115

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Fuel System Diagnosis

060R200182

6E2–116

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Circuit Description

When the ignition switch is turned  “ON”, the powertrain
control module (PCM) will turn “ON” the in-tank fuel
pump.  The in-tank fuel pump will remain “ON” as long as
the engine is cranking or running and the PCM is receiving
58X crankshaft position pulses.  If there are no 58X
crankshaft position pulses, the PCM will turn the in-tank
fuel pump “OFF” 2 seconds after the ignition switch is
turned “ON” or 2 seconds after the engine stops running.
The in-tank fuel pump is an electric pump within an
integral reservoir.  The in-tank fuel pump supplies fuel
through an in-line fuel filter to the fuel rail assembly.  The
fuel pump is designed to provide fuel at a pressure above
the pressure needed by the fuel injectors.  A fuel pressure
regulator, attached to the fuel rail, keeps the fuel available
to the fuel injectors at a regulated pressure.  Unused fuel
is returned to the fuel tank by a separate fuel return line.

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. Connect the fuel pressure gauge to the fuel feed line

as shown in the fuel system illustration.  Wrap a
shop towel around the fuel pressure connection in
order to absorb any fuel leakage that may occur
when installing the fuel pressure gauge.  With the
ignition switch “ON” and the fuel pump running, the
fuel pressure indicated by the fuel pressure gauge
should be 333-376 kPa (48-55 psi).  This pressure
is controlled by the amount of pressure the spring
inside the fuel pressure regulator can provide.

3. A fuel system that cannot maintain a constant fuel

pressure has a leak in one or more of the following
areas:

D

The fuel pump check valve.

D

The fuel pump flex line.

D

The valve or valve seat within the fuel pressure
regulator.

D

The fuel injector(s).

4. Fuel pressure that drops off during acceleration,

cruise, or hard cornering may case a lean condition.
A lean condition can cause a loss of power, surging,
or misfire.  A lean condition can be diagnosed using
a Tech 2.  If an extremely lean condition occurs, the
oxygen sensor(s) will stop toggling.  The oxygen
sensor output voltage(s) will drop below 500 mV.
Also, the fuel injector pulse width will increase.

IMPORTANT:

Make sure the fuel system is not

operating in the “Fuel Cut-Off Mode”.

When the engine is at idle, the manifold pressure is
low (high vacuum).  This low pressure (high vacuum)
is applied to the fuel pressure regulator diaphragm.
The low pressure (high vacuum) will offset the
pressure being applied to the fuel pressure regulator
diaphragm by the spring inside the fuel pressure
regulator.  When this happens, the result is lower fuel
pressure.  The fuel pressure at idle will vary slightly as
the barometric pressure changes, but the fuel
pressure at idle should always be less than the fuel
pressure noted in step 2 with the engine “OFF”.

16.Check the spark plug associated with a particular

fuel injector for fouling or saturation in order to
determine if that particular fuel injector is leaking.  If
checking the spark plug associated with a particular
fuel injector for fouling or saturation does not
determine that a particular fuel injector is leaking,
use the following procedure:

D

Remove the fuel rail, but leave the fuel lines and
injectors connected to the fuel rail.  Refer to

 Fuel Rail

Assembly in On-Vehicle Service.

D

Lift the fuel rail just enough to leave the fuel injector
nozzles in the fuel injector ports.

CAUTION: In order to reduce the risk of fire and
personal injury that may result from fuel spraying on
the engine, verify that the fuel rail is positioned over
the fuel injector ports and verify  that the fuel injector
retaining clips are intact.

D

Pressurize the fuel system by connecting a 10 amp
fused jumper between B+ and the fuel pump relay
connector.

D

Visually and physically inspect the fuel injector
nozzles for leaks.

17.A rich condition may result from the fuel pressure

being above 376 kPa (55 psi).  A rich condition may
cause a DTC P0132 or a DTC P0172 to set.
Driveability conditions associated with rich
conditions can include hard starting (followed by
black smoke) and a strong sulfur smell in the
exhaust.

20.This test determines if the high fuel pressure is due

to a restricted fuel return line or if the high fuel
pressure is due to a faulty fuel pressure regulator.

21.A lean condition may result from fuel pressure

below 333 kPa (48 psi).  A lean condition may
cause a DTC P0131 or a DTC P0171 to set.
Driveability conditions associated with lean
conditions can include hard starting (when the
engine is cold ), hesitation, poor driveability, lack of
power, surging , and misfiring.

22.Restricting the fuel return line causes  the fuel

pressure to rise above the regulated fuel pressure.
Command the fuel pump “ON” with the Tech 2.  The
fuel pressure should rise above 376 kPa (55 psi) as
the fuel return line becomes partially closed.

NOTE: Do not allow the fuel pressure to exceed 414 kPa
(60 psi).  Fuel pressure in excess of 414 kPa (60 psi) may
damage the fuel pressure regulator.

CAUTION: To reduce the risk of fire and personal
injury:

D

It is necessary to relieve fuel system pressure
before connecting a fuel pressure gauge.  Refer to
Fuel Pressure Relief Procedure, below.

D

A small amount of fuel may be released when
disconnecting the fuel lines.  Cover fuel line
fittings with a shop towel before disconnecting, to
catch any fuel that may leak out.  Place the towel in
an approved container when the procedure is
completed.

6E2–117

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Fuel Pressure Relief Procedure

1. Remove the fuel cap.
2. Remove the fuel pump relay from the underhood

relay center.

3. Start the engine and allow it to stall.
4. Crank the engine for an additional 3 seconds.

Fuel Gauge Installation

1. Remove the shoulder fitting cap.
2. Install fuel gauge J 34730-1 to the fuel feed line

located in front of and above the right side valve train
cover.

3. Reinstall the fuel pump relay.

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 the Tech 2 to command the fuel pump
“ON”.

(Refer to the Miscellaneous Test.)

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

6E2–118

RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Fuel System Diagnosis

  (Cont'd)

Step

No

Yes

Value(s)

Action

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

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 the Tech 2.
2. After pressure has built up, turn off the pump and

clamp the supply hose shut with suitable locking
pliers which will not damage the hose.

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, which will not damage

the hose, clamp the fuel return line to prevent fuel
from returning to the fuel tank.

3. Run the fuel pump with the 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