Isuzu engine C22NE / 22LE / 20LE. Manual — part 71

DRIVEABILITY AND EMISSIONS 6E1-113

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 ELECTRICAL TEST

Circuit Description

When the ignition switch is first turned ON, the engine

control module (ECM) energizes the fuel pump relay

which applies power to the in-tank fuel pump. The fuel

pump relay will remain ON as long as the engine is

running or cranking and the ECM is receiving 58X

crankshaft position pulses. If no 58X crankshaft

position pulses are present, the ECM de-energizes the

fuel pump relay within 2 seconds after the ignition is

turned ON or the engine is stopped.

The fuel pump delivers fuel to the fuel rail and

injectors, then to the fuel pressure regulator. The fuel

pressure regulator controls fuel pressure by allowing

excess fuel to be returned to the fuel tank. With the

engine stopped and ignition ON, the fuel pump can be

turned ON by using a command by the scan tool.

Diagnostic Aids

An intermittent may be caused by a poor connection,

rubbed-through wire insulation, or a wire broken inside

the insulation. Check for the following items:
• Poor connection or damaged harness - Inspect the

ECM harness and connectors for improper mating,

broken locks, improperly formed or damaged

terminals, poor terminal-to-wire connection, and

damaged harness.

6E1-114 DRIVEABILITY AND EMISSIONS

Test Description

Number(s) below refer to the step number(s) on the

Diagnostic Chart.

2. If the fuel pump is operating but incorrect pressure

is noted, the fuel pump wiring is OK and the “Fuel

System Pressure Test” chart should be used for

diagnosis.

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.

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 alow 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 in front of and above the right

side valve cover.

3. Reinstall the fuel pump relay.

Fuel System Electrical Test

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 Ignition “ON”.

2. Install Scan Tool

3. Command Fuel Pump “ON”.

Did the Fuel Pump turn on?

-

Go to Fuel

System

Diagnosis

Go to Step 3

3

1. Ignition OFF.

2. Remove the fuel pump relay.

3. Using a test light connected to ground, probe the

battery feed to the relay.

Did the light illuminate?

-

Go to Step 5

Go to Step 4

4

Repair short or open battery feed to fuel pump relay.

Is the action complete?

-

Verify repair

-

5

1. Connect a test light between the two wires that connect

to the fuel pump relay pull-in coil.

2. Ignition ON.

Did the test light illuminate for 2 seconds and then turn

off?

-

Go to Step 11

Go to Step 6

6

1. With a test light connected to battery (

−), probe the fuel

pump relay connector at the wire which runs form the

relay pull-in coil to the ECM.

2. Ignition ON.

Did the test light illuminate for 2 seconds and then turn off?

-

Go to Step 7

Go to Step 8

DRIVEABILITY AND EMISSIONS 6E1-115

Fuel System Electrical Test (Cont'd)

Step

Action

Value(s)

Yes

No

7

Locate and repair open in the fuel pump relay ground

circuit. Is the action complete?

-

Verify repair

-

8

Check for short or open between the ECM and the fuel

pump relay.

Was a problem found?

-

Verify repair

Go to Step 9

9

1. Check the fuel pump relay circuit for a poor terminal

connection at the ECM.

2. If a problem is found, replace terminal as necessary.

Was a problem found?

-

Verify repair

Go to Step 10

10

Replace the EPROM or ECM.

Is the action complete?

Note) Refer to 6E1-243.

-

Verify repair

-

11

1. Reconnect the fuel pump relay.

2. Disconnect the fuel pump electrical connector at the

fuel tank

3. Using a test light connected to ground, probe the fuel

pump feed wire (harness side).

4. Command the fuel pump ON with a scan tool.

Did the light illuminate for 2 seconds?

-

Go to Step 14

Go to Step 12

12

1. Honk the horn to verify that the horn relay is

functioning.

2. Substitute the horn relay for the fuel pump relay.

3. Leave the test light connected as in step 12.

4. Command the fuel pump ON with the scan tool.

Did the test light illuminate for 2 seconds when the fuel

pump was commanded ON?

-

Go to Step 16

Go to Step 13

13

1. Re-connect the horn relay in its proper location.

2. Check for a short circuit, blown fuse or open circuit

between the relay and the fuel tank.

Is the action complete?

-

Verify repair

-

14

1. With the fuel pump electrical connector at the fuel tank

disconnected, connect a test light between the feed

wire and the ground wire (harness side).

2. Command the fuel pump ON with a scan tool.

Did the test light illuminate for 2 seconds?

-

Go to Step 17

Go to Step 15

15

Repair the open circuit in the fuel pump ground wire.

Is the action complete?

-

Verify repair

-

16

1. Re-connect the horn relay in its proper location.

2. Replace the fuel pump relay.

Is the action complete?

-

Verify repair

-

17

Replace the fuel pump.

Is the action complete?

-

Verify repair

-

6E1-116 DRIVEABILITY AND EMISSIONS