Isuzu N-Series. Service manual - part 452

6E-144 EMISSION AND ELECTRICAL DIAGNOSIS

6. Vacuum Switching Valve; Intake Throttle

Inspection

Connect the vacuum switching valve connector
terminals No.1 and No.2 to (+) terminal and (-) ter-
minals of battery respectively, and check the conti-
nuity between the ports. 
If the check result is abnormal, repair or replace the
valve.

Caution:
When measuring resistance with a circuit tester, be
careful not to damage or deform the terminals.

Legend

1. Resistance (k

Ω)

2. ECT 

°F (°C)

N6A1254E

N6A1255E

N6A1251E

EMISSION AND ELECTRICAL DIAGNOSIS 6E-145

Fast Idle Control Device (FICD) System Malfunction

N6A1677E

6E-146 EMISSION AND ELECTRICAL DIAGNOSIS

Inspection

Vacuum Switching Valve (VSV)
Resistance Check
Check the resistance between the VSV connector termi-
nals using a circuit tester. 
Cold Resistance
: 37 — 44 (

Ω) (for 12 Volt)

: 159 — 169 (

Ω) (for 24 Volt)

Connect the battery voltage between VSV connector
terminals and make sure of the continuity between the
ports.

Airtight Check
Apply negative pressure to the negative pressure input
port as illustrated on the left.

Although there is leakage, it is no problem if the negative
pressure rises to -46.7 kPa (-350 mmHg / -6.77 psi) or
more.

Caution:
When measuring resistance with a circuit tester, be
careful not to damage or deform the terminals.

Working Check
Apply powervoltage between the terminals, there is no
problem if the negative pressure does not rise when ap-
plied to the input port.

1. Diaphragm is built in the actuator, by which the in-

side of the actuator is divided into two, atmospheric
room and negative pressure room.

Legend

1. 2 Pin
2. Port

N6A1264E

N6A1265E

Legend

1. FICD actuator
2. Aneroid compensator actuator
3. Full rod set lever

N6A1266E

N6A1289E

EMISSION AND ELECTRICAL DIAGNOSIS 6E-147

2. Fast Idle Control Device (FICD) actuator link is

connected to FICD lever, setting speed control le-
ver at a specified speed when FICD is at work at
the time of idling.

3. The link of the actuator for the aneroid compensa-

tor is connected to full load set lever. The full load
set lever is connected to a U-lever. When the atmo-
spheric sensor built in Engine Control Module
(ECM) makes the actuator work, the full load set le-
ver and U-lever are rotated to a specified position

so that the control rack is drawn in the direction of
reducing fuel injection amount.

Legend

1. Vacuum chamber
2. Atmospheric chamber
3. Diaphragm

Legend

1. Speed control lever
2. FICD actuator
3. FICD lever

N6A1273E

N6A1291E

Legend

1. Aneroid compensator actuator
2. Full load set lever

N6A1274E