What is the resistance of the wavy shunt on the GPR controllers?

ifrythings

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Keep in mind your pcm does compensate for the higher system voltage, your glowplugs are self regulating and draw about half the current that these idi glowplugs use.

The idi glowplugs are 0.25 ohms cold each, that’s around 300-400 amps (depending on battery voltage) initial current and will drop to about half after they are warmed up.

Personally I think your going to have more trouble trying to fix a problem that isn’t a problem, but another option if you are worried about the higher voltage hurting your plugs, delay the alternator from turning on till the glowplugs are turned off.

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Booyah45828

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Personally I think your going to have more trouble trying to fix a problem that isn’t a problem, but another option if you are worried about the higher voltage hurting your plugs, delay the alternator from turning on till the glowplugs are turned off.

My thoughts as well.

Like your screenshot says, the pcm uses battery voltage as one of the factors for determining glow plug on time. And the pcm is pretty good at what it does and doesn't usually burn the glow plugs out. The powerstrokes don't seem to have near the issues with glow plugs as the idi engines do, and that's because of the controller and plug design.

Truthfully, @Burnt , I wouldn't worry about it. And if you are, I'd put a toggle switch on the control wire of the glow plug relay, once started, flip it off and you don't need to worry about your alternator voltage. The only reason it runs the plugs after it's running is to reduce white smoke when it's cold.
 

Burnt

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Keep in mind your pcm does compensate for the higher system voltage

Like screenshot says, the pcm uses battery voltage as one of the factors for determining glow plug on time.

As the screenshot says, "If battery voltage is abnormally high, the duty cycle is shortened to extend plug life. The glow plug relay will only cycle on and off repeatedly if there is a system high voltage condition greater than 16 volts."

So while the PCM is monitoring system voltage, it is only programmed to take action to save the glow plugs if the voltage is greater than 16 volts.

The glow plugs are rated at 11 volts, and my concern is that they are now seeing 14.2 volts.

Prior to my alternator upgrade, the glow plugs only saw 12 volts, even with the engine running.

I'm trying to solve for the 2 extra volts that they are now seeing, that they didn't previously see.

The PCM does not offer any protection or control in this range.



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ifrythings

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These truck did come with the option of dual alternators which would have enough amps to get the charging voltage up to 14v and ford would of tested this scenario and figured 16v is the limit these plugs can handle.

Keep in mind also that your pcm is monitoring the current the plugs use to determine if one burns out, adding in extra resistance could mess up the pcm operation.

Have you measured the voltage actually going to the glowplugs after the relay and metal shunt resistor? You mite be only getting 12-13v after all the connection and wire losses.
 

Burnt

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These truck did come with the option of dual alternators which would have enough amps to get the charging voltage up to 14v and ford would of tested this scenario and figured 16v is the limit these plugs can handle.

My truck indeed has that dual alternator option, and Ford did indeed test that very scenario. And this must be why Ford commands the second alternator to remain off until the glow plugs are commanded off. So having two alternators is the same as having one alternator, as long as the glow plugs are commanded on. The one alternator that Ford brings online (a stock 110a alternator) only generates 50 amps at idle, and as such there is typically a system wide voltage drop to about 12v while the glow plugs are still commanded on, regardless of whether the truck is optioned with single or dual alternators, in the stock configuration.


Keep in mind also that your pcm is monitoring the current the plugs use to determine if one burns out, adding in extra resistance could mess up the pcm operation.

I'm not sure that this is the case in Federal 49 state trucks that do not have the California Glow Plug Monitor (GPM) Relay. Even in those trucks that have the GPM, the PCM is not able to determine individual glow plug failure, only a fault with the left bank or the right bank, as whole banks, not as individual plugs. Later California emissions equipped trucks came equipped with a solid state Glow Plug Control Module (GPCM). This device is able to provide diagnostic feedback on the status of individual glow plugs, but requires a PCM calibration, a pin populated PCM connector, and the engine wiring harness outfitted with all the wires required to connect a GPCM. I have none of these.

With just a simple Federal Glow Plug Relay (GPR), I don't know how the PCM can know the status of individual glow plugs, or even the status of the left or right banks of glow plugs. There doesn't seem to be the physical means present to communicate that information to the PCM.

While the language of the service manual suggests that the PCM "controls" the glow plugs based on barometric pressure (BARO, to infer altitude), engine oil temperature (EOT), and B+ voltage, the level of actual "control" does not appear to be as sophisticated as the language suggests, even though the language is truthful.

For EOT, the PCM refers to a look up table that assigns a certain number of seconds for on time, based on EOT, from 0 seconds at any temperature at or above 131°F, to the full 120 seconds at any temperature at or below 20°F, with a more or less linear rate of change between these two extremes, with only two changes of time/temp rates when graphed.

For BARO, if the absolute atmospheric pressure is 11.34 PSIA (equivalent to 7,000 feet elevation at 34°F) or below, the PCM will simply add 5 seconds to the time chart under EOT, still not to exceed 120 seconds total. While this simple additive measure can still be technically considered "control", it is not that sophisticated, and is not going to save glow plugs from idiots like me who feed them too much voltage with aftermarket parts.

We've already discussed the PCM's monitoring of voltage. If above 16 volts, throttle back. Else, let er' rip.

So this is why I became interested in looking back a decade, to the Glow Plug Controller (GPC), which at first glance to me appeared to have stand alone, autonomously functioning features to protect glow plugs. That's why I had to come to an IDI forum, to learn more about it.

Have you measured the voltage actually going to the glowplugs after the relay and metal shunt resistor? You mite be only getting 12-13v after all the connection and wire losses.

My truck, with a Federal relay, does not have any type of shunt resistor. The voltage at the power pin on the relay that feeds the glow plug is the same voltage as the B+ terminal behind the alternator. Some type of shunt resistor is what I was fantasizing about adding to my relay, to get the exact effect that you describe. This may or may not work as I imagined though, but I haven't learned enough one way or the other to discontinue pursuit of the idea.

I really appreciate all efforts to help. Even if my answers may seem to shoot down each question or idea presented, my intent is only to supply the actual facts of the situation, so that you can better help me with ideas and solutions.

In general, the folks who know how to keep older vehicles alive, tend to have a lot more can do that the folks who trade in their vehicles before the warranty expires, so I really do value the participation and help that I am receiving here.
 
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snicklas

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@Burnt

I hate to say it, but you are giving the 7.3 IDI Style "Solid State" glow plug controller WAY too much credit. There is really no intelligent control of the plugs. That Z-Shaped Resistor is there only to measure current draw, it does not limit the voltage to the glow plugs. The IDI controller, has only one "input". This one input, being a "key-on" hot, that energizes the controller when you turn on the key. The controller pulls the white wire on the relay to ground, to energize the relay. The relay closes and sends battery voltage through the Z-Shaped resistor and to the plugs. At this point the actual voltage at the plugs is in the 7-8 volt range due to the massive draw on the system. As the glow plugs heat up, their resistance increases, drawing less current. As the current decreases to a set point that is "sensed" by the controller, the controller should (I've had them do this, and not) go into afterglow. This afterglow pulses the relay on an off, to keep the plugs hot without overheating. This afterglow can last up to 2 minutes. There is no over-voltage protection in the IDI's. The controller going into afterglow quickly due to a burned out plug(s) is because the system is drawing less current to begin with, and gets to the "set" point faster, it's not to protect the rest of the plugs. The glow plugs that are used in an IDI are actually 6 Volt glow plugs. This was done so they would heat up quickly, so there was not a long delay in being able to start the truck. These trucks were competing with gassers, and there are customers that would not but a diesel if there were inconvenienced have to wait for an extended time for the plugs to heat.

This thing is basically an on-off system that monitors current draw to determine how hot the plugs are. You can make a very simple manual override of this controller (even keeping it connected to operate as it should) by connecting a grounded push button to the same post as the white wire. Push the button, and the plugs are on until you take your finger off the button, no matter what the controller is doing.
 

franklin2

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@Burnt

I hate to say it, but you are giving the 7.3 IDI Style "Solid State" glow plug controller WAY too much credit. There is really no intelligent control of the plugs. That Z-Shaped Resistor is there only to measure current draw, it does not limit the voltage to the glow plugs. The IDI controller, has only one "input". This one input, being a "key-on" hot, that energizes the controller when you turn on the key. The controller pulls the white wire on the relay to ground, to energize the relay. The relay closes and sends battery voltage through the Z-Shaped resistor and to the plugs. At this point the actual voltage at the plugs is in the 7-8 volt range due to the massive draw on the system. As the glow plugs heat up, their resistance increases, drawing less current. As the current decreases to a set point that is "sensed" by the controller, the controller should (I've had them do this, and not) go into afterglow. This afterglow pulses the relay on an off, to keep the plugs hot without overheating. This afterglow can last up to 2 minutes. There is no over-voltage protection in the IDI's. The controller going into afterglow quickly due to a burned out plug(s) is because the system is drawing less current to begin with, and gets to the "set" point faster, it's not to protect the rest of the plugs. The glow plugs that are used in an IDI are actually 6 Volt glow plugs. This was done so they would heat up quickly, so there was not a long delay in being able to start the truck. These trucks were competing with gassers, and there are customers that would not but a diesel if there were inconvenienced have to wait for an extended time for the plugs to heat.

This thing is basically an on-off system that monitors current draw to determine how hot the plugs are. You can make a very simple manual override of this controller (even keeping it connected to operate as it should) by connecting a grounded push button to the same post as the white wire. Push the button, and the plugs are on until you take your finger off the button, no matter what the controller is doing.

All that complicated stuff he was describing is on the newer truck he is working on. He came into our forum to figure out how the older system worked and possibly retro fit part of it into his newer system. I think he knows now how "dumb" our controllers are. My controller is even dumber, it's my thumb pushing a button.
 

Booyah45828

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All that complicated stuff he was describing is on the newer truck he is working on. He came into our forum to figure out how the older system worked and possibly retro fit part of it into his newer system. I think he knows now how "dumb" our controllers are. My controller is even dumber, it's my thumb pushing a button.

Mine too.

Like I said, if you're worried about it, put a toggle switch on the control side of the glow plug relay. When the engine is running, flip the switch off, and you don't have to worry about voltage or how long the computer keeps the plugs on.

Once the engine is running, the only reason they have the plugs on is to keep the chamber hot to clear up the exhaust.
 

Burnt

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Once the engine is running, the only reason they have the plugs on is to keep the chamber hot to clear up the exhaust.

And that is exactly why I was trying to find a way to go ahead and keep the glow plugs on for the factory time duration, and just limit their exposure to more voltage than the factory figured they would be exposed to.

A custom tune can also terminate the glow plugs from staying on, without even wiring a switch, but I actually was hoping to try and keep the glow plugs on for that brief period of time, so as to reduce cold start exhaust emissions, because the only one who will be breathing those emissions is me, as I'll be nearest to the truck while it is warming up.
 

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