SYSTEM OVERVIEW DESCRIPTION
The solid state glow plug system consists of the glow plug controller (mounted on rear of intake manifold), glow plug harness assembly, and glow plugs. The system determines glow plug temperature by electronically measuring the resistance of glow plugs. It then maintains this temperature regardless of ambient temperature.
The afterglow operation of the glow plugs continues after the "WAIT TO START" light turns off. The glow plugs cycle on and off for a period of time. This helps reduce white smoke after engine start-up. The system can be recycled by turning ignition off and on. The engine can be started as soon as the "WAIT TO START" light goes off.
GLOW PLUG DESCRIPTION
The system uses positive temperature coefficient (PTC) glow plugs. The resistance of the glow plugs changes as the temperature rises. The glow plugs use bullet type terminals. (Scheme 18)
Scheme 18
GLOW PLUG CONTROLLER DESCRIPTION
The power relay is mounted on top of the solid-state controller circuit board. The complete assembly is mounted on the rear of the intake manifold. (Scheme 19)
Scheme 19
WAIT TO START LAMP DESCRIPTION
The "WAIT TO START" lamp comes on when the ignition switch is turned to the RUN position, and the engine is below normal operating temperature. It will remain lit for 4 to 10 seconds, depending on engine temperature. If engine is at or above normal operating temperature the lamp will not turn on.
Note. If the ignition switch is left in the ON position for an extended period of time or the engine is not started within two minute cycling time, the glow plug system must be reset by turning the ignition switch to OFF position.
GLOW PLUG FAILURE ANALYSIS
The following are examples of glow plug failure. Each example gives a different clue to glow plug failure analysis.
- There is no visible damage, but glow plug is electrically open (Scheme 20) This indicates an internal heating element failure.
- Glow plug tip that is missing can be caused by incorrect timing or poor fuel quality (Scheme 21)
- Multiple, distorted glow plugs are usually caused by electrical overheating (Scheme 22) A complete evaluation of the glow plug control system should be made.
Scheme 20
Scheme 21
Scheme 22
PINPOINT TEST A1 - CHECK HARNESS
With Ignition switch in the OFF position remove leads from glow plugs. Check continuity between glow plug terminal and power source with glow plugs installed in engine. If OK, go to PINPOINT TEST A2. If not OK, replace plug(s) and go to PINPOINT TEST A2.
Scheme 23
PINPOINT TEST A2 - CHECK HARNESS
With Ignition switch in the OFF position remove leads from glow plugs. Remove the protective cover of control unit by squeezing sides (Scheme 24) Check continuity between each glow plug lead and test terminal of control unit. (Scheme 25)
Are all leads OK? If yes go to PINPOINT TEST A3. If no service or replace harness and go to PINPOINT TEST A3.
Scheme 24
Scheme 25
PINPOINT TEST A3 - CHECK CONTROL UNIT
With ignition switch in the OFF position contact ohmmeter to ground wire terminal eyelet and to ground post on each battery (Scheme 26)
If less than 1 ohm go to PINPOINT TEST A4. If more than 1 ohm clean or service ground connection, Repeat check and go to PINPOINT TEST A4.
Scheme 26
PINPOINT TEST A4 - CHECK SUPPLY VOLTAGE
With ignition switch in the OFF position connect voltmeter to control unit power terminal and ground (Scheme 27)
If more than 10 volts go to PINPOINT TEST A5. If less than 10 volts, service wiring or recharge battery and go to PINPOINT TEST A5.
Scheme 27
PINPOINT TEST A5 - CHECK VOLTAGE FROM IGNITION SWITCH
Connect voltmeter to ignition terminal on control unit and ground. Turn ignition switch to the ON position and all accessories off (Scheme 28)
If voltage is more than 8 volts go to PINPOINT TEST A6. If voltage is less than 8 volts, check fusible link, service wiring or recharge battery and go to PINPOINT TEST A6.
Scheme 28
PINPOINT TEST A6 - FUNCTIONAL TEST
With ignition switch in the OFF position connect 12 volt test light to test terminal on control unit (Scheme 29) Position test light so it can be viewed from driver's position. Turn ignition switch to ON position and monitor system operation. Compare test light times to test light table below.
Scheme 29
Note. Total Test Light "ON" Time includes time from the beginning of the initial "ON" cycle to the end of the last "ON-OFF" cycle measured in seconds.
| Control Unit Temp. °F (1) | "Wait-To-Start" Lamp "ON" Time (Sec.) | Test Light Total Time (Sec.) |
|---|---|---|
| 20°C | 7-15 | 35-70 |
| 0°F | 7-12 | 25-60 |
| 35°F | 5-12 | 15-35 |
| 70°F | 3-5 | 7-15 |
| 105°F | 1-3 | 3-5 |
| 140°F | 1 OR LESS | 1-3 |
| (1) Temperature of Control Unit, Not ambient temperature. | ||
| (1) | Temperature of Control Unit, Not ambient temperature. |
TEST LIGHT TIME
Note. The "Wait-To-Start" Lamp and/or Test Light may not illuminate if engine temperature is at or near normal operating Temperature.
If test light times are within specifications, system function is correct. If test light times are out of specifications, disconnect power at both batteries and replace control unit, repeat test.
PINPOINT TEST B1 - "WAIT-TO-START" LAMP STAYS ON
Disconnect the "Wait-To-Start" lamp connector at control unit (Scheme 30) Turn ignition switch to ON position.
If lamp goes ON service wiring to lamp. If lamp does not go ON disconnect power at both batteries and replace control unit.
Scheme 30
PINPOINT TEST B2 - "WAIT-TO-START" LAMP DOES NOT GO ON
Disconnect the "Wait-To-Start" lamp connector at control unit. Connect jumper wire from harness side to ground (Scheme 31) Turn ignition switch to ON position.
If lamp goes ON, there is a "Hard Start" problem; glow plugs are OK. See appropriate TROUBLE SHOOTING procedure in FUEL INJECTION SYSTEM - DIESEL. If lamp does not go ON replace bulb or service wiring.
