Isuzu engine C22NE / 22LE / 20LE. Manual — part 58

DRIVEABILITY AND EMISSIONS 6E1-61

A/C Clutch Control Circuit Diagnosis (Cont'd)

Step

Action

Value(s)

Yes

No

5

1. Ignition OFF.

2. Disconnect the Engine Control Module (ECM)

connectors from the ECM.

3. Check the A/C Compressor Clutch Relay control circuit

between the ECM and Underhood Electrical Center for

the following conditions:

• A Short to ground
• An open circuit
• A short to voltage
Was the problem found?

-

Verify Repair

Go to Step 6

6

1. Reinstall the A/C Compressor Clutch Relay.

2. Using a fused jumper, ground the A/C Compressor

Clutch Relay control circuit at the ECM connector.

3. Ignition ON, Engine OFF.

Does the A/C Compressor turn ON?

-

Go to Step 9

Go to Step 7

7

1. Ignition OFF.

2. Check the A/C Compressor Clutch circuit between the

A/C Compressor Clutch Relay and A/C Compressor

Clutch for the following conditions:

• A Short to ground
• An open circuit
• A short to voltage
Was the problem found?

-

Verify Repair

Go to Step 8

8

Replace the A/C Compressor Clutch Relay.

Is the action complete?

-

Verify Repair

-

9

Replace the EPROM or ECM.

Note) Refer to 6E1-243

-

-

-

6E1-62 DRIVEABILITY AND EMISSIONS

ELECTRONIC IGNITION SYSTEM

DIAGNOSIS

If the engine cranks but will not run or immediately

stalls, the Engine Cranks But Will Not Start chart

must be used to determine if the failure is in the

ignition system or the fuel system. If DTC19, or

DTC18 is set, the appropriate diagnostic trouble code

chart must be used for diagnosis.

If a misfire is being experienced refer to the

Symptoms section for diagnosis.

EVAP CANISTER PURGE CONTROL

SOLENOID (IF APPLICABLE)

A continuous purge condition with no purge

commanded by the ECM will set a DTC62. Refer to

the DTC charts for further information.

VISUAL CHECK OF THE

EVAPORATIVE EMISSION CANISTER

(IF APPLICABLE)

• If the canister is cracked or damaged, replace the

canister.

• If fuel is leaking from the canister, replace the

canister and check hoses and hose routing.

IDLE AIR CONTROL (IAC) VALVE

The Scan Tool displays the IAC pintle position in

counts. A count of “O” indicates the ECM is

commanding the IAC pintle to be driven all the way

into a fully-seated position. This is usually caused by

a vacuum leak.

The higher the number of counts, the more air is

being commanded to bypass the throttle blade. Refer

to IAC System Check in order to diagnose the IAC

system. Refer to Rough, Unstable, or Incorrect Idle,

Stalling in Symptoms for other possible causes of idle

problems.

FUEL SYSTEM PRESSURE TEST

A fuel system pressure test is part of several of the

diagnostic charts and symptom checks. To perform

this test, refer to Fuel System Diagnosis.

DRIVEABILITY AND EMISSIONS 6E1-63

FUEL METERING SYSTEM CHECK

Some failures of the fuel metering system will result

in an “Engine Cranks But Will Not Run” symptom. If

this condition exists, refer to the Cranks But Will Not

Run chart. This chart will determine if the problem is

caused by the ignition system, the ECM, or the fuel

pump electrical circuit.

Refer to Fuel System Electrical Test for the fuel

system wiring schematic.

If there is a fuel delivery problem, refer to Fuel System

Diagnosis, which diagnoses the fuel injectors, the fuel

pressure regulator, and the fuel pump.

Followings are applicable to the vehicles with

closed Loop System:

If a malfunction occurs in the fuel metering system, it

usually results in either a rich HO2S signal or a lean

HO2S signal. This condition is indicated by the HO2S

voltage, which causes the ECM to change the fuel

calculation (fuel injector pulse width) based on the

HO2S reading. Changes made to the fuel calculation

will be indicated by a change in the long term fuel trim

values which can be monitored with a Scan Tool. Ideal

long term fuel trim values are around 0%; for a lean

HO2S signal, the ECM will add fuel, resulting in a fuel

trim value above 0%. Some variations in fuel trim

values are normal because all engines are not exactly

the same. If the evaporative emission canister purge is

02 status may be rich condition. 02 status indicates the

lean condition, refer to DTC44 for items which can

cause a lean HO2S signal.

FUEL INJECTOR COIL TEST

PROCEDURE AND FUEL INJECTOR

BALANCE TEST PROCEDURE

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart:
2. Relieve the fuel pressure by connecting 5-8840-

0378-0 T-Joint to the fuel pressure connection on

the fuel rail.

Caution: In order to reduce the risk of fire and

personal injury, wrap a shop towel around the

fuel pressure connection. The towel will

absorb any fuel leakage that occurs during

the connection of the fuel pressure gauge.

Place the towel in an approved container

when the connection of the fuel pressure

gauge is complete.

Place the fuel pressure gauge bleed hose in an

approved gasoline container.

With the ignition switch OFF open the valve on the

fuel pressure gauge.

3. Record the lowest voltage displayed by the DVM

after the first second of the test. (During the first

second, voltage displayed by the DVM may be

inaccurate due to the initial current surge.)

Injector Specifications:

Resistance Ohms

Voltage Specification at

10°C-35°C (50°F-95°F)

11.8-12.6

5.7-6.6

• The voltage displayed by the DVM should be

within the specified range.

• The voltage displayed by the DVM may

increase throughout the test as the fuel injector

windings warm and the resistance of the fuel

injector windings changes.

• An erratic voltage reading (large fluctuations in

voltage that do not stabilize) indicates an

intermittent connection within the fuel injector.

5. Injector Specifications:

Highest Acceptable Voltage

Reading Above/Below

35°C/10°C (95°F/50°F)

Acceptable

Subtracted

Value

9.5Volts

0.6Volt

7. The Fuel Injector Balance Test portion of this

chart (Step 7 through Step 11) checks the

mechanical (fuel delivery) portion of the fuel

injector. An engine cooldown period of 10 minutes

is necessary in order to avoid irregular fuel

pressure readings due to “Hot Soak” fuel boiling.

6E1-64 DRIVEABILITY AND EMISSIONS

Injector Coil Test Procedure (Steps 1-6) and Injector Balance Test Procedure (Steps 7-11)

CYLINDER

1

2

3

4

1st Reading (1)

296kPa

(43psi)

296kPa

(43psi)

296kPa

(43psi)

296kPa

(43psi)

2nd Reading (2)

205kPa

(29psi)

205kPa

(29psi)

196kPa

(28psi)

274kPa

(39psi)

Amount of Drop

(1st Reading-2nd Reading)

91kPa

(14psi)

91kPa

(14psi)

100kPa

(15psi)

22kPa

(4psi)

Av. Drop = 166kPa/24psi

±10kPa/1.5psi

= 156

− 176kPa or

22.5

− 25.5psi

Faulty, Lean

(Too Little

Fuel Drop)

Faulty, Lean

(Too Little

Fuel Drop)

Faulty, Lean

(Too Little

Fuel Drop)

Faulty, Lean

(Too Little

Fuel Drop)

NOTE: These figures are examples only.