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I got one of these older trucks in the other day for a no start and the clicking relay problem. Of course coming into the business in 2005 I have only worked on these a few times before so its all new to me. This seems to be a common issue that is unique to this Glow plug system and is more complicated than even the newer 7.3L Powerstroke versions. After all the reading up on the system in the Ford manuals etc. I have come to have a good understanding of the system. In doing so I wanted to walk you through how to diagnose it and how it works sounds and reacts to bad glow plugs. This way costly good parts don't get changed out.

 

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90 7.3 idi non-turbo 4x4
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this is extreamly helpful thank u for doing this video my truck is doing the exact same thing and im going to fix it this weekend thank u
 

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your information is off base. these are very simple systems, not over complicated or over engineered.
the reason they are completely different than the powerstroke system is because the powerstroke glow plug system is computer controlled.
the idi dos not have a computer. so it needs a solid state controller to make the relay work.
also, ht eunit is temp controlled. once the engine reaches around 110-120 degrees it shuts off. the "clicking" of the system is actually an afterglow function to limit smoke on warmup.
 

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Discussion Starter #5
your information is off base. these are very simple systems, not over complicated or over engineered.
the reason they are completely different than the powerstroke system is because the powerstroke glow plug system is computer controlled.
the idi dos not have a computer. so it needs a solid state controller to make the relay work.
also, ht eunit is temp controlled. once the engine reaches around 110-120 degrees it shuts off. the "clicking" of the system is actually an afterglow function to limit smoke on warmup.
My information is dead on straight from the book, the complicated thing is a matter of opinion and is debatable. If you have ever seen a 7.3l powerstroke with just a relay how can you argue these IDI's are simple, there is just no need for all this extra modules and wires and measuring system.
Of course the powerstroke relay is pcm controlled that's what makes it so simple. If you watch the video the constant clicking on and off is not normal and at the end after I fixed the truck you can see when it was done heating up the cylinders it just shut off. Now CYCLING on and off for a period of time after startup is normal yes to reduce white smoke and emission yes, but that is cycling not constant clicking. All constant clicking does is wear the internal high amperage contacts in the relay not normal. See here- A copy and paste from the Ford PCED explaining the system. I do not fix Fords everyday by not knowing how these systems work.

------Figure 15: Solid State Glow Plug Control System
The system determines the glow plug temperature by electronically measuring the resistance of the glow plugs. It then maintains this temperature regardless of ambient temperatures.

The system is actuated when the ignition switch is turned to the RUN position. The "WAIT TO START" indicator lights until the glow plugs reach the proper temperature. The indicator goes out and the engine can be started.

The afterglow operation of the glow plugs continues after the "WAIT TO START" indicator turns off. The glow plugs cycle on and off for a period of time. This helps to reduce white smoke after engine start-up.

The glow plug system can be recycled by turning the ignition off and on. This immediately restarts the glow plug cycle. The engine can be started as soon as the "WAIT TO START" indicator goes off.

Glow Plugs
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 (Figure 17).
 

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i don't pay attention to books, there are way to many mistakes in them, even ford service manuals. i go by owning and working on them for the past 30 years.
they are very simple systems. as long as you do not try to over think repairing them.
 
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