SYSTEM OVERVIEW
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 1)
Scheme 1
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 2)
Scheme 2
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 3) This indicates an internal heating element failure.
- Glow plug tip that is missing can be caused by incorrect timing or poor fuel quality (Scheme 4)
- Multiple, distorted glow plugs are usually caused by electrical overheating (Scheme 5) A complete evaluation of the glow plug control system should be made.
Scheme 3
Scheme 4
Scheme 5
PINPOINT TEST A1 - CHECK HARNESS
With Ignition switch in the OFF position, remove leads from glow plugs. Check for continuity between the glow plug terminal and the power source with the glow plugs installed in the engine. (Scheme 6) If okay, proceed to PINPOINT TEST A2 - CHECK HARNESS. If not okay, replace glow plug(s) and go to PINPOINT TEST A2 - CHECK HARNESS.
Scheme 6
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 7) Check continuity between each glow plug lead and test terminal of control unit. (Scheme 8)
If all leads test okay, go to PINPOINT TEST A3 - CHECK CONTROL UNIT . If leads are not okay, service or replace harness and go to PINPOINT TEST A3 - CHECK CONTROL UNIT .
Scheme 7
Scheme 8
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 9)
If less than 1 ohm, proceed to PINPOINT TEST A4 - CHECK SUPPLY VOLTAGE . If more than 1 ohm, clean or service ground connection, Repeat check and go to PINPOINT TEST A4 - CHECK SUPPLY VOLTAGE .
Scheme 9
PINPOINT TEST A4 - CHECK SUPPLY VOLTAGE
With ignition switch in the OFF position connect voltmeter to control unit power terminal and ground (Scheme 10)
If more than 10 volts, proceed to PINPOINT TEST A5 - CHECK VOLTAGE FROM IGNITION SWITCH . If less than 10 volts, service wiring or recharge the battery and proceed to PINPOINT TEST A5 - CHECK VOLTAGE FROM IGNITION SWITCH .
Scheme 10
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 11)
If voltage is more than 8 volts, go to PINPOINT TEST A6 - FUNCTIONAL TEST . If voltage is less than 8 volts, check fusible link, service wiring or recharge battery and go to PINPOINT TEST A6 - FUNCTIONAL TEST .
Scheme 11
PINPOINT TEST A6 - FUNCTIONAL TEST
With ignition switch in the OFF position connect 12 volt test light to test terminal on control unit (Scheme 12) 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 12
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 13) 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 13
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 14) Turn ignition switch to ON position.
If lamp goes ON, there is a Hard Start problem; glow plugs are okay. See appropriate TESTS W/O CODES article. If lamp does not go ON, replace bulb or service wiring.
