Isuzu engine 4j series. Instruction - page 91

QOSII PREHEATING SYSTEM 6D6 – 1

SECTION 6D6

QOSII PREHEATING SYSTEM

(4JB1/4JB1T/4JB1TC ONLY)

CONTENTS

PAGE

General Description....................................................................................................... 6D6 - 1

System Diagram............................................................................................................. 6D6 - 2

Inspection on QOS II system Operation ...................................................................... 6D6 - 3

QOSII System Troubleshooting.................................................................................... 6D6 - 4

GENERAL DESCRIPTION

QOS II preheating system features a quick-on glow
plug with thermometer control of the glowing time and
the afterglow time function.

The system consists of a controller, indicator lamp,
thermoswitch, relay, and glow plug ( 4 pcs).

With the employment of the thermoswitch, the glow
time changes according to the engine coolant
temperature, thus allowing optimum starting conditions
to be obtained.

6D6 – 2 QOSII PREHEATING SYSTEM

SYSTEM DIAGRAM

QOS II Timing Chart

6D6-2-1.tif

6D6-2-2.tif

QOSII PREHEATING SYSTEM 6D6 – 3

Inspection on QOSII System Operation
THERMO SWITCH

The thermo switch is located on the water outlet pipe.

Use a circuit tester to check the thermo switch for continuity.

OFF

!ON

: 7-13°C (44.6-55.4°F)

ON

!OFF

: Below 3°C (37.4°F)

10°C

ON

OFF

3°C

GLOW PLUG

Use a circuit tester to test the glow plugs for continuity.

Glow Plug Resistance (Reference)

Ohms

Conventional model

Approximately 1.5

Quick on start model

Approximately 0.9

6D6-3-1.tif

6D6-3-2.tif

6D6-3-3.tif

6D6 – 4 QOSII PREHEATING SYSTEM

QOSII SYSTEM TROUBLESHOOTING

Problems when the water temperature of the engine is 0°C below.

Condition

Cause

Circuit

Glow plug relay will
not be lit.

Bad connection of FLW between battery and starter.

Bad connection or disconnection of starter SW circuit

Bad connection or disconnection

Malfunction of other

of Fuse No . 8

circuits occurred
simultaneously.

Bad starter awitch.

Bad connection of glow plug relay terminal.

Disconnection of glow plug relay excitation coil.

Disconnection of circuit between glow plug relay and timer.

Bad glow relay. (The main contact does not pass electricity.)

Bad connection of timer.

Bad timer.

Bad earth circuit of timer.

Bad thermoswitch. (It remains ON even in water temperature below 0°C.)

Earth short-circuiting of thermo SW.

3

2

1

6

7

7

6D6-4-1.tif

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