My Glow Plug System Dilemma....AntennaClimber this is for you...:)

[Asmoday]

Hello All,

I've been reviewing some posts on here about the proper operation, etc. of the Glow Plug system including the controller card and even though I'll probably sound like a goof for admitting this I finally realized my current system does not work correctly...LOL.

A little history...

When I purchased my M1009 the GP system was stock with the firewall resistor intact, everything wired correctly and functioning perfectly. It had the heavy duty USA made later model GP relay (higher coil resistance) and the controller card functioned correctly as per the TM's. When I would start it the glow plugs always cycled on and off correctly during the "afterglow" phase.

I began to become very paranoid about GP swelling and after having my fears confirmed I decided to do the popular "GP Relay mod" and removed the firewall resistor, sourced the 12V source for the GP relay directly from the 12v distribution bus above the rear battery, replaced the GP relay with a brand new Trombetta 974-1215-011-09 as this relay exactly matched the one removed with reference to Ohm resistance, load etc. It's a direct military replacement, US made and Trombetta was a supplying contractor. Glow plugs were replaced with the AC-60G's and all contacts on the controller card were cleaned. All connectors for the wiring at the GP relay were replaced, soldered and heat shrinked and glow plug connectors were replaced with the proper ones for the 60G's.

The system has performed flawlessly with one exception...The system does not cycle on and off during the 'afterglow' phase. After starting the GP relay just stays closed for a particular duration energizing the glow plugs and then that is it.

My system in original stock form ALWAYS cycled the glow plugs on and off. The modified system has NEVER cycled them on and off.
The GP controller card was replaced with a CUCV Electric "Legacy" card and it made no difference. All the wiring was checked as per the TM -20 and it's all correct. Voltage is correct...no low voltage issues and even the batteries are now new.

My question is...why... What has changed to cause the system to NOT cycle the glow plugs on and off correctly?

 

[antennaclimber]

You have a good question.
I have noticed the same situation with my three CUCV vehicles as well. Two have the resistor bypass and one was converted to 12 volts by the previous owner.


When you modify the voltage source to the glow plugs (resistor bypass procedure) from the factory 24 volt source, it is highly unlikely that the GP card will see a voltage high enough at the monitoring point for it to go in to a GP protection mode. The GP card starts to cycle the GP relay to protect the GP's from being supplied with excessive voltage normally above a nominal 12.5 VDC.

As stated in the GP Module Theory of Operation:
"If the voltage on the GP side of the relay exceeds approximately 12.5 volts, the GPM will cycle the glow plug relay on and off to protect the glow plugs......"

The next paragraph states:

"If the glow plugs are supplied directly with 12 volts and resistor is not connected, the GPM will continue to monitor the voltage to the glow plugs and will cycle the relay if the voltage exceeds the 12.5 volt threshold."
Your system is not exceeding the protection threshold.

Now one may ask "But my alternators are putting out 14.2 volts once the engine is running".
True, however a properly functioning GP system with all 8 GP's lit up, will be drawing about 100 amps. The IR (voltage) drop in the (now modified) wiring to the GP's will drop the voltage at the monitoring point on the GP card to below the nominal 12.5 volt protection threshold.

So the simple answer is:
Due to voltage drops across the wiring, the glow plug card does not need to cycle the glow plugs to protect them.

If you vehicle does start to cycle the glow plugs, I would check the glow plugs to see if any fail the resistance check. Or you may have an alternator putting out excessive voltage.

Karl

 

[doghead]

Karl, your reply sounds like you are referring only to the rapid clicking that occurs when the GPs are burned out or when the relay is bad.

What about the afterglow issue that he was asking about.


Mine does afterglow and is supplied with 12v.

 

[antennaclimber]

Eric,

I apologize for not being clear. I was referring to the afterglow in my answer, not relay chatter or fast cycles. I should have specified this.

It all depends on the voltage that the GP card monitor is seeing to determine afterglow cycle rate if its needed.

Some vehicles may indeed have a higher GP voltage than others due to condition of batteries, alternator output, wiring condition, splices, improper crimp connections, poor connections, starter cranking time, ambient temperature, age of glow plug card, component tolerances and the resistance of the glow plugs themselves. There are quite a few variables that will affect the outcome. Each one of them or a combination of them will lower the monitor voltage, especially when the supply voltage is only a couple of volts above the threshold to begin with. This is a high current circuit and voltage drop is going to happen especially if there are poor connections. And we all know that the CUCV is full of them.

I have a M1009 that sometimes it does the afterglow and sometimes it does not. No clue as to why but fortunately the system works when it needs to.

Usually relay chatter is caused by a defective GP card. And as many of us know, faster than normal relay cycling is usually one or more defective glow plugs.

I hope this helps to clear things up.

Karl

 

[Asmoday]

Awesome info...! Thank you...!

 

[Recovry4x4]

Hello All,


A little history...


I began to become very paranoid about GP swelling and after having my fears confirmed I decided to do the popular "GP Relay mod" and removed the firewall resistor, sourced the 12V source for the GP relay directly from the 12v distribution bus above the rear battery, replaced the GP relay with a brand new Trombetta 974-1215-011-09 as this relay exactly matched the one removed with reference to Ohm resistance, load etc. It's a direct military replacement, US made and Trombetta was a supplying contractor. Glow plugs were replaced with the AC-60G's and all contacts on the controller card were cleaned. All connectors for the wiring at the GP relay were replaced, soldered and heat shrinked and glow plug connectors were replaced with the proper ones for the 60G's.



My question is...why... What has changed to cause the system to NOT cycle the glow plugs on and off correctly?

Isn't the buss above the rear battery 24V?

 

[Asmoday]

Good catch... I was mistaken... I wound up going to the junction block on the firewall... That is what I meant to write...

 

[Asmoday]

So...while looking for another issue recently posted on the forum I double checked by voltages at the GP relay both before and after starting the truck while the GP relay in on providing voltage to the glow plugs.

The one thing I found that still baffles me is once started...the voltage being delivered to the glow plugs is over 14v. I verified the voltage source lead (orange) that goes to the controller card is good and the controller card is also seeing the 14v while the glow plugs are energized yet my glow plugs do not do the after glow on and off cycle...

They just stay on for a duration....cycle off and that's it....

I swapped in a new CUCV Electrics controller card and no change...

 

[sierrajcharlie]

So...while looking for another issue recently posted on the forum I double checked by voltages at the GP relay both before and after starting the truck while the GP relay in on providing voltage to the glow plugs.

The one thing I found that still baffles me is once started...the voltage being delivered to the glow plugs is over 14v. I verified the voltage source lead (orange) that goes to the controller card is good and the controller card is also seeing the 14v while the glow plugs are energized yet my glow plugs do not do the after glow on and off cycle...

They just stay on for a duration....cycle off and that's it....

I swapped in a new CUCV Electrics controller card and no change...

I installed a voltmeter, 12v, on the output of my gpr so I could monitor the voltages. I have done the resistor bypass so it's just the 12 volts supplying the relay.

I saw that I was only getting about 9-10 volts at the turn of the key. As seconds passed the voltage would increase to just below 12 volts, if I let the plugs heat until the card shut down to protect the plugs. There was no afterglow once they shut down. This is during the summer months when the temps were anywhere from 75-100 degrees. I was concerned about the low readings so I again cleaned up all connections and even replaced the engine ground and the wires for the batteries. Now my voltages at the turn of the key were 11 volt. Success.

Now the weather has turned cooler, below 40, and I'm having start up issues. It'll start but it takes 3 starts of 5 seconds and the right amount of fuel. They also now do the afterglow and at that time it 's getting 14.4 volts, right where the alt's are charging. In reading this thread I'm again thinking of replacing the plugs, Bosch's. I checked them before I replaced the wires and they all tested at 1.1-1.8 ohms.

So, is it time for a new set of plugs..... Replace the fuel filter...... (Crap) Have the IP rebuilt.........don't have the funds for that one.......... Or my favorites......... Sell it, blow it up, use it for target practice, beat it with a ball bat. etc etc etc These probably aren't the most productive things but after 3 years of fighting it I'm just about ready to throw in the towel.

 

[Asmoday]

Well....it has been getting colder where I'm at now and after starting the output of the relay where it's distributed to the GP's shows about 14.4 volts as well but my system still does not do an "after glow" on and off cycle. I thought the controller card was supposed to do this but no go on my truck...

 

[forest522]

I have the same issue...have had no troubles at all but I can tell there is no afterglow occuring. With the exception of the thermistor, everything checks out.

This is a great thread. The discussions regarding the GP system here are exactly why some many come to this forum. Outstanding advice and information from AntennaeClimber!! Thank you!!

 

[sierrajcharlie]

An update on my 09. I was having longer start-ups than I was happy with so I decided to replace the plugs with 60g’s. The Bosch’s were a couple of years old so I thought it wouldn’t hurt anything. I had checked the resistance of the plugs in the motor a month or so ago and they tested between 1.1 and 1.8 on the 6 I checked.


So after the swap it’s starting in a couple of seconds, a big improvement. I tested the old plugs again and found 7 at 0 and one at 2.5 ohms. Apparently testing them in the block gives a second or two of greater resistance. Lesson learned.

The controller still would give the 12 second wait light and keep power to the plugs for 40-45 seconds. I would start it a couple of seconds after the wait light would go out. Now once in a while I would get the afterglow. If it did it three times after it was running I would get a second of relay chatter on the last heat cycle. I didn’t care for that, so I removed the card and am just using the push-button. According to the voltmeter I had installed, using the card I would get 9 volts that would increase to 11 volts at the turn of the key. Using the push button I get the 12 volts right away.

So it looks like the card is giving me a problem, thanks for the explanation in this thread!
[FONT=&quot]We’ll see, I’ll just use the button for now, maybe I’ll get a new card later[/FONT]

 

[scottladdy]

I just want to check my understanding:

Afterglow = energizing the glow plugs after a successful engine start for a time determined by the glow plug module based on sensor inputs. This is not to be confused with glow plug over voltage protection which will cause the relay to cycle DURING the afterglow.

Relay Cycling (off/on) = performed by the glow plug module to prevent an over voltage condition from occurring and burning out the glow plugs. Trigger voltage on the glow plug side of the glow plug relay is 12.5 volts for off.

So, if I don't observe relay cycling during the afterglow, that means the glow plug module never "sees" an over voltage (> 12.5V) on the glow plug side of the relay. Assuming all components are working properly.

Now, assuming my understanding is correct, I think there may be some common confusion that the relay cycling is an indication of afterglow. When, in fact it is an indication that the glow plug module is "seeing" greater than 12.5 V and working to protect the glow plugs.

Personally, I determine whether or not my trucks are in afterglow based on the voltage meter. With about a 100 watt draw, system voltage drops noticeably to the top of the yellow band. All of my trucks have the resistor bypass implemented, with no relay cycling occurring since the bypass.

Relay cycling due to over voltage is more likely to occur when the glow plugs are fed by the 24 volt bus through the resistor bank. It is also more likely to occur with the older style non-current limiting glow plugs.

I will start a diagnostic if I notice relay cycling, as this is likely an indication that something is wrong. I will also start a diagnostic if I do not see the voltage meter drop to it's "usual" spot, as this is likely an indication that the overall current draw is low, possibly due to a faulty glow plug.

Please correct/amend where my understanding is inaccurate or incomplete.

Thanks.

 

[antennaclimber]

Scottladdy.

I agree with your statement. Very nice write up.

The only thing I would change is;

Relay Cycling (off/on) = performed by the glow plug module during the afterglow period to prevent an over voltage condition from occurring and burning out the glow plugs. Trigger voltage on the glow plug side of the glow plug relay is approximately 12.5 volts for off.

And you have that stated correctly here:

Afterglow = energizing the glow plugs after a successful engine start for a time determined by the glow plug module based on sensor inputs. This is not to be confused with glow plug over voltage protection which will cause the relay to cycle DURING the afterglow.

Relay cycling occurs during the afterglow period to protect the GP's.

If I notice any of my vehicles cycling during the afterglow period, I might have a problem that needs attention. Watching the voltmeter is a good way to keep an eye on things.

I added a second voltmeter to Blazer B that monitors the GP voltage when the GP relay is closed then switches to the 12 volt side of the electrical system when the GP relay opens. This lets me know the voltage to the GP's to see if the GP relay and associated components are functioning properly.

Karl

 

[scottladdy]

... I added a second voltmeter to Blazer B that monitors the GP voltage when the GP relay is closed then switches to the 12 volt side of the electrical system when the GP relay opens. This lets me know the voltage to the GP's to see if the GP relay and associated components are functioning properly.

Nice. Could I impose on you for a wiring diagram of that hookup?

Thanks for the critique. Hoping this thread reduces confusion.

 

[antennaclimber]

Nice. Could I impose on you for a wiring diagram of that hookup?

Thanks for the critique. Hoping this thread reduces confusion.

I finally had time to find my second voltmeter drawing.

It is very important to install a fuse in the orange and positive lines going to the relay. This is not shown in the drawing. The fuse should be as close as possible to the source.
Karl

View attachment GP Voltage Monitor Relay.pdf