Isuzu engine C22NE / 22LE / 20LE. Manual — part 73
DRIVEABILITY AND EMISSIONS 6E1-121
Fuel System Diagnosis (Cont'd)
Step
Action
Value(s)
Yes
No
19
Locate and correct the restriction in the fuel return line.
Is the action complete?
-
Verify repair
-
20
Visually and physically inspect the fuel rail outlet passages
for a restriction.
Was a restriction found?
-
Verify repair
Go to Step 11
21
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
22
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
23
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
B2
0.5
GRN
B7
A3
5 Volt
Reference
Signal
MAP Sensor
Input
Sensor
Ground
0.75
L
B8
0.75
G
B1
A B
C
Intake
Air Temperature
Sensor
Throttle Position
Sensor
Engine
Control
Module
(ECM)
HI
OUT
LO
0.5
G
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
No
1
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
2
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
3
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
4
Repair the seal rubber (color : orange) to ensure the hose
supplies vacuum to the MAP sensor only
Is the action complete?
-
Verify repair
-
5
Check the sensor connection.
Is the sensor connection good?
-
Go to Step 6
Go to Step 7
6
Replace the sensor. Refer to On-Vehicle Service, MAP
Sensor.
Is the action complete?
-
Verify repair
-
7
Repair the poor connection.
Is the action complete?
-
Verify repair
-
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