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Isuzu engine C22NE / 22LE / 20LE. Manual - part 73

DRIVEABILITY AND EMISSIONS 6E1-121

Fuel System Diagnosis (Cont'd)

Step

Action

Value(s)

Yes

Locate and correct the restriction in the fuel return line.

Is the action complete?

Verify repair

Visually and physically inspect the fuel rail outlet passages

for a restriction.

Was a restriction found?

Verify repair

Go to Step 11

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

1. Command the fuel pump ON with the Scan Tool.

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.

Does the fuel pressure indicated by the fuel pressure

gauge rise above the first specified value?

Caution: Do not let the fuel pressure exceed the

second specified value.

376 kPa

(55 psi)

414 kPa

(60 psi)

Go to Step 11

Go to Step 7

1. Command the fuel pump ON with the Scan Tool.

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

6E1-122 DRIVEABILITY AND EMISSIONS

DRIVEABILITY AND EMISSIONS 6E1-123

0.5

YEL/

GRN

0.5

GRN

0.5

RED

0.5

RED

0.5

GRN

0.5

RED

Manifold

Absolute

Pressure

(MAP)

Sensor

F10

0.5

GRN

5 Volt

Reference

Signal

MAP Sensor

Input

Sensor

Ground

0.75

A B

Intake

Air Temperature

Sensor

Throttle Position

Sensor

Engine

Control

Module

(ECM)

OUT

0.5

MANIFOLD ABSOLUTE PRESSURE (MAP) OUTPUT CHECK

Circuit Description

The manifold absolute pressure (MAP) sensor

measures the changes in the intake MAP which result

from engine load (intake manifold vacuum) and engine

speed changes; and converts these into a voltage

output. The engine control module (ECM) sends a 5-

volt reference voltage to the MAP sensor. As the MAP

changes, the output voltage of the sensor also

changes. By monitoring the sensor output voltage, the

ECM knows the MAP. A lower pressure (low voltage)

output voltage will be about 1-2 volts at idle. Higher

pressure (high voltage) output voltage will be about 4-

4.8 volts at wide open throttle. The MAP sensor is also

used, under certain conditions, to measure barometric

pressure, allowing the ECM to make adjustments for

different altitudes.

Test Description

Important: Be sure to use the same diagnostic test

equipment for all measurements.

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

the Diagnostic Chart.

1. When you compare the Scan Tool readings to a

known good vehicle, it is important to compare

vehicles that use MAP sensors that have the same

part number.

2. Applying 34 kPa (10 Hg) vacuum to the MAP

sensor should cause the voltage to be 1.5-2.1 volts

less than the voltage at step 1. Upon applying

vacuum to the sensor, the change in voltage

should be instantaneous. A slow voltage change

indicates a faulty sensor.

3. Check the vacuum hose to the sensor for leaking

or restriction. Be sure that no other vacuum

devices are connected to the MAP hose.

Important: Make sure the electrical connector

remains securely fastened.

4. Disconnect the sensor from the bracket. Twist the

sensor with your hand to check for an intermittent

connection. Output changes greater than 0.10 volt

indicate a bad sensor.

6E1-124 DRIVEABILITY AND EMISSIONS

Manifold Absolute Pressure (MAP) Output Check

Step

Action

Value(s)

Yes

1. Turn the ignition OFF and leave it OFF for 15 seconds.

2. Ignition ON. Do not crank engine.

3. The Scan Tool should indicate a manifold absolute

pressure (MAP) sensor voltage.

4. Compare this scan reading to the scan reading of a

known good vehicle obtained using the exact same

procedure as in Steps 1-4.

Is the voltage reading the same +/

−0.40 volt?

Go to Step 2

Go to Step 5

1. Disconnect the MAP sensor and plug the hole on the

intake manifold.

2. Using an adequate rubber hose, connect a hand

vacuum pump to the MAP sensor.

3. Check for the following condition:

• MAP port sealing rubber damaged or split?
• Intake vacuum leaks at;
• Vacuum leaks at throttle body;
If a problem is found, repair as necessary.

Was a problem found?

4. Start the engine.

5. Apply 34 kPa (10 Hg) of vacuum and note the voltage

change.

Is the voltage change 1.5-2.1 volts less than step 1?

Go to Step 3

Go to Step 4

No trouble found. Check the sensor seal rubber (color :

orange) for leakage or restriction.

Does the hose supply vacuum to the MAP sensor only?

Go to Step 5

Go to Step 4

Repair the seal rubber (color : orange) to ensure the hose

supplies vacuum to the MAP sensor only

Is the action complete?

Verify repair

Check the sensor connection.

Is the sensor connection good?

Go to Step 6

Go to Step 7

Replace the sensor. Refer to On-Vehicle Service, MAP

Sensor.

Is the action complete?

Verify repair

Repair the poor connection.

Is the action complete?

Verify repair

Content .. 71 72 73 74 ..