Ok, let me start off by saying I don't own any diesels and haven't any opportunities to tinker with one and figure things out, so if I sound ignorant to subject it's cause I am. How do glow plugs work? I've been told three ways: First, the plugs run non-stop until the truck is warm; Second, the plugs fire with an intense heat into the cylinder before startup to ease startup(this would kinda explain the "wait to start" light on the dash); Third, they fire shortly before TDC similar to the operation of a spark plug. If these are all wrong please correct me so I can correct the guys that told me! Thanks for all your help, as always!
Scott

 

Here is some info, the GPs are glow plugs so they glow red hot under controlled conditions, they warm up the cylinder and precombustion air. Since diesel fuel ignites with heat and extreme pressure, so the gp provide the heat, the injectors provide the squirt of fuel, and the cylinder compression makes it all explode........at the righ time.


93 year info.......other than fuses mentioned the 7.3 system is basically the same.

GLOW PLUG CONTROL
HOW THE CIRCUIT WORKS
The Glow Plug Control circuit applies power to the Glow Plugs, which heat the combustion chambers so that the diesel engine can be started.

Glow Plug Controller
The solid-state Glow Plug Controller, attached to the top of the engine block, controls the Glow Plug pre-glow and after-glow time. It also controls the circuit’s operation by sensing engine temperature, Glow Plug voltage and after-glow voltage
from the start/run circuit.

When the Ignition Switch is turned to START or RUN, voltage from Maxi-fuse K is applied through the Glow Plug Controller to the Wait-To-Start Indicator Lamp.
The Glow Plugs heat up in zero to fifteen seconds, depending on engine coolant temperature. After the Glow Plugs heat up, the controller cycling switch opens and turns the Wait-To-Start Indicator Lamp off. The Glow Plugs are now warm enough for the engine to be started.

At the same time the Ignition Switch is turned to RUN, voltage from Maxi-fuse K is applied to the after-glow timer (located inside the Glow Plug Controller). The after-glow timer cycles the Glow Plugs for up to two minutes, depending on engine temperature. The after-glow timer then opens. The Wait-To-Start Indicator Lamp will not light during the after-glow period.
If the Ignition Switch is turned OFF, it can be turned to ON immediately, and the Glow Plug heating cycle will start again.

Diesel Start/Run
The diesel engine uses two batteries to provide extra power for starting and Glow Plug heating. Power is applied from the batteries, through heavy gauge wires, to the Starter Solenoid (located in the Starter Motor assembly). When the Wait-To-Start Indicator goes out, the Ignition Switch can be turned to START.

With the Ignition Switch in START or RUN, voltage is supplied to the Fuel Heater, Fuel Shutoff Solenoid, and the Engine Temperature Switch through Maxi-fuses K and U.
The Fuel Heater is in the Fuel Filter/Separator. It heats the diesel fuel, melting any wax that might clog the filter. The heater has an internal thermostat to turn it on as needed at 32*F.

The Fuel Shutoff Solenoid controls the flow of fuel into the injection pump. With the Ignition Switch in START or RUN, the Solenoid is energized, and fuel is allowed to flow into the injection pump. When the Ignition Switch is turned off, the solenoid is deenergized, fuel flow stops, and the engine stops running.

The Engine Temperature Switch provides voltage to the Cold Timing Advance Solenoid and the Cold Idle Solenoid. When the engine temperature is below 112°F (44°C), the Engine Temperature Switch is closed. When the Ignition Switch is turned to START or RUN, the solenoids are energized, advancing injection pump timing and engine idle, allowing the engine to run more smoothly when cold. When the engine temperature reaches 112°F (44°C), the Engine Temperature Switch opens. This deenergizes the solenoids, returning the timing and idle to normal.

 

So the GP run before startup to preheat the cylinder, and run non-stop during engine operation...correct?
Scott

 

The GPs will cycle after the WTS light goes out, ON THE SOLID STATE CONTROLLER you should hear a click, click and your volt meter should swing back and forth when... ""The after-glow timer cycles the Glow Plugs for up to two minutes, depending on engine temperature. "" Now when the volt meter is steady 12V the GPs are done working.....

 

So the glow plugs, in short, are to keep a cold diesel running to warm up a bit.
Scott

 

In a round about way.......... the GPs continue to cycle to assist in eliminating the white smoke generated in a cold cylinder(s) when the engine has been started. GP cycling is shut down when their resistance increases to a point where the cylinder temps are suitable so as to not cause further smoke. The controller reads the higher resistance and shuts down the after glow/start sequence. If the controller is operating correctly.......

 

Thanks for your help
Scott

 

Does anyone have a diagram of the sensor? What wires go where, it says in one thread about the small wires and an orange one but my has neither. Does anyone have that diagram and how much voltage should be in each.