Isuzu engine C22NE / 22LE / 20LE. Service manual — part 72

DRIVEABILITY AND EMISSIONS 6E1-117

A13

Fuel

Injectors

M

Battery Joint Cable

ECM

Fuse

15A

1.25

R/W

1.25

R/W

A4

A5

Engine

Fuse

15A

Canister Purge

Control Solenoid Valve

E16

Engine

Control

Module

(ECM)

Fuel

Pump

Relay

Fuel Pump Fuse

20A

0.5

P/W

0.85

B/Y

FUEL SYSTEM DIAGNOSIS

Circuit Description

When the ignition switch is turned ON, the engine

control module (ECM) 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 ECM is

receiving 58X crankshaft position pulses. If there are

no 58X crankshaft position pulses, the ECM 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 duel leakage that may

6E1-118 DRIVEABILITY AND EMISSIONS

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 283-376 kPa (41-55

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:
• The fuel pump check valve.
• The fuel pump flex line.
• The valve or valve seat within the fuel pressure

regulator.

• 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 Scan Tool.

Following are applicable to the vehicle with

closed Loop System:

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:
• 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.

• 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.
•••• Pressurize the fuel system by connecting a

20 amp fused jumper between B+ and the

fuel pump relay connector.

•••• 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 45 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 44 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 scan tool.

The fuel pressure should rise above 376 kPa (55

psi) as the fuel return line becomes partially

closed.

Notice: 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:
• It is necessary to relieve fuel system

pressure before connecting a fuel pressure

gauge. Refer to Fuel Pressure Relief

Procedure, below.

• 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 disconnect is

completed.

DRIVEABILITY AND EMISSIONS 6E1-119

Fuel Pressure Relief Procedure

1. Remove the fuel cap.

2. Located on the intake manifold which is at the top

right part of the engine.

3. Start the engine and allow it to stall.

4. Crank the engine for an additional 3 seconds.

Fuel Pressure Gauge Installation

1. Remove the shoulder fitting cap.

2. Install fuel pressure gauge 5-8840-0378-0 to the

fuel feed line located on the upper right side of the

engine.

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 Scan Tool 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?

283-376 kPa

(41-55 psi)

Go to Step 3

Go to Step 17

3

Does the fuel pressure indicated by the fuel pressure

gauge remain constant?

Note: The fuel pressure will drop when the fuel pump

stops running, then it should stabilize and remain constant.

-

Go to Step 4

Go to Step 12

4

1. When the vehicle is at normal operating 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:
• The in-pipe fuel filter.
• 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:
• The fuel pump strainer for a restriction.
• The fuel line for a leak.
• 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

6E1-120 DRIVEABILITY AND EMISSIONS

Fuel System Diagnosis (Cont'd)

Step

Action

Value(s)

Yes

No

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 Scan Tool.

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 the Scan Tool.

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 the Scan Tool.

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