rockbender
Full Access Member
I was fortunate enough to receive a file folder full of receipts and miscellaneous information when I got my van, and amongst that information is a copied page which looks to be an excerpt from a service manual for a 6.9. The page that I have describes how the glow plug controller works and it is a bit different than I've read here in my some of my searches so I thought I would share. Feel free to chime in if you know this to be true, false, or otherwise. It's a bit long, so I apologize in advance:
"The 'quick start; afterglow' system is used to enable the engine to start more quickly when the engine is cold. It consists of the flour* (???) glow plugs, the control module, two relays, a glow plug resistor assembly, coolant temperature switch, clutch and neutral switches and connecting wire. Relay power and feedback circuits are protected by fuse links in the wiring harness. The control module is protected by a separate 10A fuse in the fuse panel."
"When the ignition is turned to the on position, a Wait-to Start signal appears near the cold-start knob on the panel. When the signal appears, relay No. 1 also closes and full system voltage is applied to the glow plugs. If engine coolant temperature is below 86 deg F, relay No. 2 also closes at this time. After three seconds, the control module turns off the WTS light indicating that the engine is ready for starting. If the ignition switch is left in the ON position about three seconds more without cranking, the control opens relay No. 1 and current to the plugs stops to prevent overheating. However, if coolant temperature is below 86 deg F when relay No. 1 opens, relay No. 2 remains closed to apply reduced voltage to the plugs through the glow plug resistor until the ignition switch is turned off. "
"When the engine is cranked, the control module cycles relay No. 1 intermittently. Thus, glow plug voltage will alternate between 12 and zero volts with relay No. 2 open. After the engine starts, alternator output signals the control module to stop the No. 1 relay cycling and the afterglow function takes over."
"If the engine coolant temperature is below 86 deg. F, the No. 2 relay remains closed. This applies reduced (4.2 - 5.3) voltage to the glow plugs through the glow plug resistor. When the vehicle is under way (clutch and neutral switches closed), or coolant temperature is over 86 deg F, the control module opens relay No. 2, cutting off all current to the glow plugs."
*flour - this was copied verbatim from the sheet. I'm not sure if this was suppose to be 'four' making it for some other application? Everything else including the adjacent schematic points towards the 6.9 system.
In a nutshell, what this tells me is that the stock controller would hold the plugs at 12V for no longer than 6 seconds, and then reduce the voltage. I never realized that the system changed the voltage output. I had heard information about appropriately sized wire to force a voltage drop to the plugs, but don't recall reading that it worked in this manner. All of a sudden it makes since as to why we have plugs that are rated for 6 volts and how we would rarely burn them out off of a good functioning controller but roast them all the time with our pushbutton systems. It also makes me think that it would be better for the plugs on a manual system to hold for 6 seconds, and then alternate a bit - on 3, off three, on 3 off three.
Ideally, I'd like to have a second pushbutton (or a three way momentary toggle would be perfect!) so that I could apply 12v for 6 seconds or so to get things fired up, and then hold them in their warmed up state with the 6V for another 6-10 seconds without worry about burning them up.
I'm hoping that Mel might be able to chime in or update his thread on the new 6.9 controller that he put it. Now that I understand the actual logic of the controller I'm thinking it is going to be smarter than me and my big fat thumb!
"The 'quick start; afterglow' system is used to enable the engine to start more quickly when the engine is cold. It consists of the flour* (???) glow plugs, the control module, two relays, a glow plug resistor assembly, coolant temperature switch, clutch and neutral switches and connecting wire. Relay power and feedback circuits are protected by fuse links in the wiring harness. The control module is protected by a separate 10A fuse in the fuse panel."
"When the ignition is turned to the on position, a Wait-to Start signal appears near the cold-start knob on the panel. When the signal appears, relay No. 1 also closes and full system voltage is applied to the glow plugs. If engine coolant temperature is below 86 deg F, relay No. 2 also closes at this time. After three seconds, the control module turns off the WTS light indicating that the engine is ready for starting. If the ignition switch is left in the ON position about three seconds more without cranking, the control opens relay No. 1 and current to the plugs stops to prevent overheating. However, if coolant temperature is below 86 deg F when relay No. 1 opens, relay No. 2 remains closed to apply reduced voltage to the plugs through the glow plug resistor until the ignition switch is turned off. "
"When the engine is cranked, the control module cycles relay No. 1 intermittently. Thus, glow plug voltage will alternate between 12 and zero volts with relay No. 2 open. After the engine starts, alternator output signals the control module to stop the No. 1 relay cycling and the afterglow function takes over."
"If the engine coolant temperature is below 86 deg. F, the No. 2 relay remains closed. This applies reduced (4.2 - 5.3) voltage to the glow plugs through the glow plug resistor. When the vehicle is under way (clutch and neutral switches closed), or coolant temperature is over 86 deg F, the control module opens relay No. 2, cutting off all current to the glow plugs."
*flour - this was copied verbatim from the sheet. I'm not sure if this was suppose to be 'four' making it for some other application? Everything else including the adjacent schematic points towards the 6.9 system.
In a nutshell, what this tells me is that the stock controller would hold the plugs at 12V for no longer than 6 seconds, and then reduce the voltage. I never realized that the system changed the voltage output. I had heard information about appropriately sized wire to force a voltage drop to the plugs, but don't recall reading that it worked in this manner. All of a sudden it makes since as to why we have plugs that are rated for 6 volts and how we would rarely burn them out off of a good functioning controller but roast them all the time with our pushbutton systems. It also makes me think that it would be better for the plugs on a manual system to hold for 6 seconds, and then alternate a bit - on 3, off three, on 3 off three.
Ideally, I'd like to have a second pushbutton (or a three way momentary toggle would be perfect!) so that I could apply 12v for 6 seconds or so to get things fired up, and then hold them in their warmed up state with the 6V for another 6-10 seconds without worry about burning them up.
I'm hoping that Mel might be able to chime in or update his thread on the new 6.9 controller that he put it. Now that I understand the actual logic of the controller I'm thinking it is going to be smarter than me and my big fat thumb!