glow plug controller questions.

[Redneck]

I was inspired today to start getting my road slug back on the road. I spent the required time lying on top of the engine wondering if I was undoing the appropriate bolts, and giving my hands a coating of that special brand of grease and gunk only a diesel can produce.
Now I'm at the point when I can actually see the offending piece of electronics, and I'm trying to decide what route to go.
I've checked the service records, and the GP controller hasn't been touched since '01.
I've been told there's a way to bypass the controller completely by creating my own extension for the GP harness, that would connect to a "ford starter solenoid" and be on a momentary switch from in the cab.
This appeals to me for the price ($25 a solenoid, instead of $250 for a new controller). However, I can't find anymore info on it...Any of you Oilburners know how this deal works???
The other option is to buck up and buy a new controller, and wire a momentary switch to it like in the tech article at the top of the forum.

Anyone have any info for me??

 

[franklin2]

Is this the 91? If so, just take the white wire off the controller and tape it. Take a new wire and hook it to the terminal where the white wire used to be, run it into the cab to a momentary pushbutton switch. Hook the wire to one side of the switch, and hook another wire to the other side of the switch and run and bolt it to a good ground under the dash. Best thing I ever did to my truck, and a friend's truck also.

 

[Redneck]

I'm pretty sure the controller's pooched though because all the plugs are good, but the plugs aren't cycling.

 

[plywood]

That solenoid on top is a separate entity really. It may be good where as the controller under it is bad.

To find out just turn the key on and hook a jumper wire from the terminal with the white wire to ground for just a second, if it clicks solid, your solenoid is probably good.

Then you can do as posted, and have a manual control just like that.

 

[Redneck]

Well hot damn wouldn't that be schnazzy if I could have the tow rig up and runnin that easy! I know what I'm doin tomorrow after work..

 

[argve]

in most cases I have found that the controller is good along with the solenoid - what the problem typically is either bad glow plugs (which you have tested and ruled out) then typically what I see is the problem is just plain ole bad connections. Clean up all the connections on the glow plug controller and the solenoid and see what happens.

I did up how the controller works for ya... hold on...

 

[argve]

Here is how the system works.

When you turn on the key the controller is activated and it closes the relay that is mounted on top of the controller then it reads how much voltage is dropped across the Glow Plugs. As current flows through the system it has a fixed resistance in which to use (the big zig zag piece of metal on the controller) so it waits until the voltage on the glow plugs comes up to a set point. We don't know what this voltage set point is and really we don't need to know.

What happens is as the glow plugs heat they change resistance value - they actually increase in ohmic value so as they increase in ohms they become more of a restriction to current flow and so they will increase their voltage drop. Once the voltage drop gets high enough the controller knows that they are HOT HOT HOT and so it switches to a pulsing action so to keep them at that temp and not burn out. Once it switches to the pulsing it will turn off the WAIT TO START LAMP in the cab to let you know to start the truck. Once it has pulsed the glow plugs with power for I think it's 10 seconds or so it will shut down and wait for another key cycle before they will work.

By key cycle I mean OFF and then back ON.

In 70 degree weather the glow plugs are sitting at a higher temp from the get go than in 30 degree weather so the controller will not run the glow plugs for as long because remember as the glow plugs heat they gain resistance and since they are already warmer (it's summer time now) the controller will see it's magical set point voltage sooner because the plugs don't have to heat as long as say they do when the outside temp is at 30 degrees.

Now if you have at least one glow plug that is not working this will fool the controller in that it thinks the plugs are warmer than they actually are.

This is because the glow plugs are in parallel so we know from OHM's law that you as remove resistors in a parallel circuit that the overall resistance increases for that section of the circuit. Well because the resistance increased then so will our voltage drop across that section of the circuit, so the controller is looking at the voltage from backside of the zig zag resistor to ground and it will see that magical voltage sooner so the plugs did not get enough time to heat fully.

This is what causes short cycling as some call it. Where the controller only ran the wait to start lamp for a very short period of time and will go right into pulsating the plugs. So then you have a hard start condition.

Typically you can get away with one bad glow plug and not really see too much of difference unless you really pay close attention - with two glow plugs not working your gonna have a hard time getting her to start and you'll know there is a problem. With 3 or more bad glow plugs if you get it started in the cold you got dang lucky.

 

[Redneck]

So all the plugs are good, and when I hit the switch, I hear the controller clicking loudly.
When I attach a test light to the end of the gp harness wire though, the light doesn't light up when the switch is pressed.
Harness is pooched?

 

[Redneck]

Ok, called Wilson and Proctor, the local heavy diesel shop and talked to their head mechanic.
He said to go to Lordco (our local jobber), and get a constant heavy duty solenoid, PN SNLS512A.
It's a 4 post solenoid, 2 heavy posts, connect power from the battery to one, and the end of the GP harness to the other large post.
There are two smaller posts on the front, attach a ground to one, and the momentary switch wire to the other.
Bam there ya go.

Is that right?

 

[plywood]

Pretty much, although I would check first to see if your harness is bad, usually when the solenoid is clicking loudly it's good, but it still could be bad.

Also, the controller will not work right if you have a bad harness, it causes the same issue as having bad plugs.

You can build your own harness, and that may be all you need.

 

[Redneck]

Built my own harness.
Wired it as I was told.
Right now I have a switch that has a ground wire and a wire to the solenoid, it's a two terminal switch.
If I put 12v to the solenoid post the switch is connected to the solenoid clicks and heats the glowplugs. If I click the switch though, nothing happns. Should I have 12v to the switch, then to the solenoid?
Seems to me there should be a ground involved, not just the one on the solenoid.

 

[Redneck]

Well it seems my previous post was correct. Ran power to switch and then from switch to small solenoid post, clicked switch for 15 seconds and it started.
We congratulated ourselves for awhile, then noticed a puddle of diesel under it.
Tomorrow we tackle that gremlin.
Also ended up with an extra bolt somehow, but can't find any hole for it...maybe I found it rolling loose and mistakenly added it to the bolt bucket.
Also gotta loose that soup bowl.