Glow plug controller?

[dmaxjoe]

My 84 was converted to the solid state controller and bullet glow plugs. The wait to start light stays on for 30 seconds. I changed the controller thinking it was sticking, but the new one is the same. What would make this happen?

 

[franklin2]

What type glowplugs do you have? If they are not stock motorcraft or international, they will affect the glow time.

 

[dmaxjoe]

Motorcraft Beru's. I also changed the plug on the main harness because the old one was corroded.

 

[Dave 001]

What is the ambient temperature?

 

[Wyreth]

What is the ambient temperature?

"Location: Burton, Michigan"

I'm guessing F'ing cold.... which would lead to long WTS times.

 

[dmaxjoe]

My 91 on the same day will glow for 16 seconds. I guess if the glow plugs are ok with it, I am also. I just don't know what the difference in the 2 are.

 

[Wyreth]

Well something is causing low impedance. The solid state controller uses impedance to check GP temp. As the temp on the plugs goes up, so does their impedance. So, if you're getting excessive glow cycles, either there is a short to ground on the hot side of the circuit, or the controller isn't grounded properly.

That's my WAG at least.

 

[Dave 001]

"Location: Burton, Michigan"

I'm guessing F'ing cold.... which would lead to long WTS times.

That was my line of thinking also.

 

[dmaxjoe]

I have been searching and reading gp controller threads, and I am still confused about the way this controller works. With one bad gp it will stay on for about 15 seconds. Change that plug for a new one, 28-32 seconds depending on outside temp. My 91 has never glowed longer than 18 seconds on the coldest of days.

 

[franklin2]

You must be registered for see images attach

See that shiny flat piece of metal that goes from the one large stud to the spot that says "glowplugs"? That is a calibrated piece of metal called a "shunt". There will be a very slight voltage drop across this piece of metal when the current is flowing to the glowplugs. The more current that flows, the more voltage across the shunt. The less current that flows, the less voltage across the shunt. This is one of the ways the controller gets info to make it's glow time decisions. That's why a faulty glowplug will throw off the current flow through the shunt, which gives the controller brain bad information. I do not know if there is any other input to the controller, like a temperature sensor or something like that.

I guess in this situation you have to make up your mind that you are going to figure this out no matter what, and start swapping things between the two trucks till you figure out what it is.

 

[dmaxjoe]

So the wires between the controller and the gp's would change glow time. I have changed the wires feeding power to the controller but not the wires to the gp's themselves. I will check them next.

 

[opusd2]

It's amazing how these things work, huh? And even greater how much some people know on this site.

 

[dmaxjoe]

This site is the reason my old trucks run as good as they do.