Nissan/Datsun 200SX/510/610/710/810/Maxima 1973-1984 Repair Guide

Diesel Engine Auto-Glow System

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Fig. Fig. 1 Glow plug electrical schematic-diesel engines

The glow plug circuit is used on diesel engines to initially start the engine from cold. The glow plugs heat up the combustion chambers prior to cranking the engine. This heat, combined with the first squirt of fuel from the injectors and the extremely high cylinder pressures, fires the engine during cold starts. After normal operating temperature is reached, the water temperature sensor wired in the glow plug system changes the system's electrical resistance and cancels glow plug operation during hot starting.

The fast glow control units on 810 and Maxima diesel engines have multiple functions, controlling various components of the glow plug system. The unit has a total of ten terminals:



No.1 Terminal: A terminal at which voltage being applied to the glow plug is measured. It serves two functions:
 

    1. Determines the pre-glow time (approx. 4 to 12 seconds)
    2.  
    3. Stops after-glow operations when a voltage of more than 7 volts is detected after pre-glow operation
    4.  




No.2 Terminal: Control unit's power source terminal
 
No.3 Terminal: Control unit's ground terminal
 
No.4 Terminal: A terminal that controls the ON/OFF operation of glow plug relay 1.
 
No.5 Terminal: A terminal connected to the water temperature sensor to serve three functions:
 

    1. Determines the period that the warning lamp remains illuminated (approx. 1 to 9 seconds)
    2.  
    3. Determines the after-glow time (approx. 5 to 32 seconds)
    4.  
    5. Stops pre-glow operation when coolant temperature is higher than 50°C (122°F)
    6.  




No.6 Terminal: A terminal connected to the START position of the ignition switch (When the ignition key is returned from START to ON, after-glow operation begins.)
 
No.7 Terminal: Controls the ON/OFF operation of glow plug relay 2.
 
No.8 Terminal: A grounding terminal for the water temperature sensor.
 
No.9 Terminal: A terminal for the flow/fuel filter warning lamp
 
No.10 Terminal: A terminal used to determine whether the engine has started or not (Glow plug relay is turned OFF by means of terminal (4) immediately after the engine has started.)
 

GLOW PLUG REMOVAL & INSTALLATION



LD28 Diesel Engine


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Fig. Fig. 2 Remove the fasteners (arrows) to remove the glow plug connector plate

  1. Disconnect the glow plug electrical leads. Remove the glow plug connecting plate.
  2.  
  3. Remove the glow plugs by unscrewing them from the cylinder head.
  4.  
  5. Inspect the tips of the plugs for any evidence of melting. If even one glow plug tip looks bad, all the glow plugs must be replaced. This is a general rule-of-thumb which applies to all diesel engines.
  6.  

To install:

To install the glow plugs, screw the glow plugs into the cylinder head just like spark plugs. Install the glow plug connecting plate. Tighten the glow plugs to 14-18 ft. lbs., and the glow plug connecting plate bolts to 12 inch lbs.

TESTING



Glow Plugs

Glow plugs are tested by checking their resistance with an ohmmeter. The plugs can be tested either while removed from the cylinder head or while still in position. To test them while removed, connect the ground side of the ohmmeter to the threaded section of the plug, and the other side to the plug's tip as shown in the illustration. If a minimum of continuity is shown on the meter, the plug is OK. If no continuity whatsoever is shown the plug must be replaced. To check the glow plugs without removing them from the cylinder head, connect the ground side of the ohmmeter to the engine block (or any other convenient ground) and the other end to the glow plug tip. Likewise, a minimum of continuity shown signifies that the plug is OK; a lack of continuity and the plug must be replaced.

GLOW PLUG CONNECTIONS





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Fig. Fig. 3 Check glow plug continuity with an ohmmeter (glow plug removed; connect the ground wire to the threaded portion)

A diesel engine's reluctance to start can often be traced to the glow plug busbar (the wire connections to the plugs.) Because diesel engines have a certain degree of vibration when running, they tend to loosen the glow plug busbars. This causes hard starting, as the plugs are not receiving their full current. Periodically tighten the wire connection to all glow plugs.


CAUTION
The Datsun/Nissan glow plug system is a 12 volt system equipped with a dropping resistor and fast glow control unit. The resistor reduces the amount of current flowing through the plugs during the after-glow period, and the glow plug control unit stops the after-glow when more than 7 volts is detected flowing through the glow plugs. Never apply a full 12 volts directly to any part of the glow plug system, especially the glow plugs themselves.

Pre-Glow System


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Fig. Fig. 4 Fast glow control unit connections



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Fig. Fig. 5 To check the pre-glow system, connect a test light to the blue/yellow wire leading into the fast glow control unit

  1. Connect a test light to the blue/yellow wire leading to the glow control unit. Measure the length of time that the test light is lighted.
  2.  
  3. Standard operation (except restart operation within 60 seconds):
  4.  

Restart operation (within 80 seconds): The length of time the light is ON should be less than 6.5 seconds. For example, when restarting the engine 5 seconds after the ignition switch is turned off, the lamp should be ON for 1.5 seconds (with engine coolant temperature below 122°F and glow plug voltage 10.5 volts).

After-Glow Operation


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Fig. Fig. 6 Check the after-glow operation as shown (terminal 7)



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Fig. Fig. 7 Test the on/off operation of the glow plug relays 1 and 2 as shown

  1. Connect a test light to the blue/red wire leading to the glow control unit. Measure the length of time that the light is lighted. In the normal condition, when the ignition switch is turned ON from ST or OFF, and the ignition switch in ST, the test light is on continuously. Refer to the accompanying illustration.
  2.  
  3. After the pre-glow system turns off, check the operation of the test light (2) in the accompanying illustration; (test light no. (1) in the illustration is OFF).
  4.  

Water Temperature Sensor

The water temperature sensor is connected to the fast glow control unit. Sensor resistance varies with changes in the temperature of the engine coolant.



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Fig. Fig. 8 Test the water temperature sensor with an ohmmeter

The sensor is tested by measuring resistance while removed from the engine and inserted in a vessel of water as shown in the illustration. Replace the sensor if resistance figures vary greatly from those shown.

 
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