Is there an 24 volt application where LB7s are used? Maybe some bigger vehicle or a boat? I'm looking for 24 volt parts like starter, glow plugs, glow plug controller. The rest, I think, can stay 12 volts as it doesn't need a lot of current.

why do you need 24volts?

Everything works fine on 12volts....especially with the junk stock batteries.

You are not going to be able to find a 24 volt glow plug controller for sure, and probably no 24volt glow plugs or starter either.

ben

why do you need 24volts?

Everything works fine on 12volts....especially with the junk stock batteries.


The rest of the vehicle this is going into is 24 volts. One of the options is to switch the duramax to 24 volts for high-amp parts (I can provide 60 amps on 12 volt subsystem right now through an existing 24->12 DC-DC converter).

You are not going to be able to find a 24 volt glow plug controller for sure, and probably no 24volt glow plugs or starter either.

ben

Bummer. I guess I'll have to figure out a different way. At this point I either have a dual 12/24 system (either by using 12->24 DC-DC converter or just using one battery for 12 and 2nd battery for 24) or I'd have to change the light bulbs/horn (not a big deal) and a few motors (could be a pain).

Thanks for the info, ben.

The starter might even work on 24 volts. Its quite heavy duty and its not like you are going to be cranking it for more than 3 seconds at a time...I know with the old VW's that were 6 volt, a lot of people converted them to 12 volt and just left the original 6 volt starter. They sure start quickly with double the voltage! :D

The glowplug controller, as I said, will be the main hurdle. It is not a simple timer with a relay like the old diesels. Its completely computer controlled by the ECM. On the LB7, you MAY be able to make it work, because all the glow plugs are bussed together, on the LLY's eachof the glow plugs are on their own individual circuit and the controller is even more advanced.

So what you might be able to do is get a really heavy duty solenoid or relay, and wire up the 24 volt glow plugs to 24volts, and to the 24 volt heavy duty relay. Then just tie the trigger of the 24 volt relay to the 12 volt output of the GPCM (glow plug control module)..so the ECM and GPCM will think its powering the glow plugs normally, when in relaity its just triggering a relay. That way the GPCM and ECM and other interior/electrical related stuff can be run on your 24v-12v DC-DC inverter, and it wont take more than 60 amps. I cant say for sure if that will work tho, the GPCM might monitor current as well, in that case it would throw a code because its sensing that there is no load on it.

How are you going to run the instrumentation? Are you going to run a stock dmax instrument cluster? You will need a custom ECM tune that has VATS (anti-theft) disabled, that way you wont need the original steering column and passlock ignition cylinder assembly...

Ben

sorry..I forgot one thing...

Is this a federal or california emmissions truck? on the cali. emmissions trucks, the glow plugs are wired individually....

Also...Im looking at the schematics and you might be able to eliminate the GPCM altogether. On the ECM, the C2 connector (I forget if C2 is the red or blue one), pin 6 is the GPCM relay control. Basically that goes +12v when the ECM wants the glow plugs ON.

Then on the ECM C1 connector, Pin 52 is the glow plug on signal wire. Its basically a feedback signal, to let the ECM know that the glow plugs are actually on; its tied to the same bus as the glow plugs, so when the glow plugs are on, its feeding 12v back into the ECM.

So you might be able to make it work by taking that GPCM relay control wire from the ECM and hooking it into your heavy duty relay (relay has to have a 12 volt coil). THen wire the 24v glow plugs to that relay. SO the ECM will trigger the relay, relay will close and turn on the 24v glow plugs. To make the ECM happy, maybe just wire the glow plug trigger wire and the glow plug on signal wire together??

I cant confirm this will work...but If I had to make a guess, thats how I would do it...

ben

The starter might even work on 24 volts. Its quite heavy duty and its not like you are going to be cranking it for more than 3 seconds at a time...I know with the old VW's that were 6 volt, a lot of people converted them to 12 volt and just left the original 6 volt starter. They sure start quickly with double the voltage! :D


Yeah, in all the 6->12 volt conversions the starter is not replaced, very true. I just thought there may have been an official 24 volt application with proper parts.


So what you might be able to do is get a really heavy duty solenoid or relay, and wire up the 24 volt glow plugs to 24volts, and to the 24 volt heavy duty relay. Then just tie the trigger of the 24 volt relay to the 12 volt output of the GPCM (glow plug control module)..so the ECM and GPCM will think its powering the glow plugs normally, when in relaity its just triggering a relay. That way the GPCM and ECM and other interior/electrical related stuff can be run on your 24v-12v DC-DC inverter, and it wont take more than 60 amps. I cant say for sure if that will work tho, the GPCM might monitor current as well, in that case it would throw a code because its sensing that there is no load on it.


I like this idea, I'll read up on the codes in the books and see what I can visually figure out from inspecting the GPCM connections. A decent DPDT relay should be able to handle the current for the glow plugs. I would have to find different glow plugs though (or modify the cycle in the computer). I suspect that glow plugs are somewhat standart (kinda like spark plugs are not engine-specific usually) and I'd just need something that won't swell at 24 volts and will have 4 times the resistance of the original 12 volt glow plugs (so that current is halved and the energy released (V^2/R) stays the same).

How are you going to run the instrumentation? Are you going to run a stock dmax instrument cluster? You will need a custom ECM tune that has VATS (anti-theft) disabled, that way you wont need the original steering column and passlock ignition cylinder assembly...

Ben

I think I'll try to incorporate the stock instrument cluster. I sent you a PM a couple of days ago asking to take a look at this thread:

http://www.dieselplace.com/forum/showthread.php?t=177721

I list what I have out of the donor vehicle and what some of the concerns I have about missing bits.

It also looks like I'll be going to dual tanks, so I'd have to sort this out in the ECM as well (as well as calibrate it to the actualy tanks/senders that I end up using). Plus it so happens that the donor vehicle was a 2wd, whereas the result is to be 4wd, so a few other ECM bits may have to be enabled.

sorry..I forgot one thing...

Is this a federal or california emmissions truck? on the cali. emmissions trucks, the glow plugs are wired individually....



I don't think it is. It wasn't shipped from CA to me, but where the truck was originally from (or even what the donor's VIN is) is not known to me. I am in CA, but I don't have to worry about emissions (not that it's really relevant to the task at hand).

I will visually inspect the GPCM when I get home to see whether I can infer how it's wired.

As for getting rid of GPCM alltogether, I could do this easily. I'll read the books and check the visual to try to infer whether GPCM is anything more than just a fancy relay. I can think of 2 things it could do:

a) Actually do the cycling

b) Keep track of the overall "GP on" time to avoid burning the glow plugs.

But then again, ECM may be the one doing all of that anyway. Unfortunately, the books and the engine are at home, so I can't run and check it out just yet, but in a couple of hours I should know.

Indeed, getting rid of the GPCM would be a good thing if I stay with the 24 volt system. I'd have to move it out of the way as it is anyway, most likely. I may have to have the exhaust go forward right over where the GPCM is.

Thanks for the good ideas, Ben :-)

sorry..I forgot one thing...

Is this a federal or california emmissions truck? on the cali. emmissions trucks, the glow plugs are wired individually....



Looks like it's CA truck. The glowplugs have individual wires coming out of the GPCM.

The ECM will check the return voltage and the range is 0-6 volts (how low it is determines how many glowplugs have gone bad). Also, the same unit seems to be housing the AI Heater relay.

Looks like what I'd have to do is use the relay idea, but make sure I drop the return voltage down to 6 volts (so it'll always think that there's a set of perfectly good glow plugs). Alternatively, there may be a way to switch the ECM to thinking that it's not a CA truck, in which case I can replace the GPCM (with the IA heater relay) with a pair of relays.

think you would be better off in long run to convert vehicle to 12 vdc, normally bulbs. that would be easier than problems from 24vdc damaging dmax ecm and other components should you get short. if you have motors that run off 24vdc, you could setup batteries to put out 24vdc to them and 12vdc to vehicle.

Just reflash the ECM to FE9 (federal emmissions) software, you will have to reflash it anyway to disable the VATS.

1. Does OBDII connector need BCM to operate?

no


2. What functionality of the instrument cluster is dependent on the BCM?
How much of the instrument cluster will operate with just ECU/TCM (speedo/tach/temp gauges?)

unfortuantly, nearly everything. The BCM controls the PMM (power mode master) functions, that is the data signal that turns the IPC on and off, etc... Im not sure if the IPC would even work without the BCM.

3. What drivetrain-related switches/control would be normally going through BCM? What should I consider replicating? E.g. Tow/Haul switch (I'm unclear whether there is one for Duromax/Allison and what it controls), O/D disable (again, not sure there was one in the first place), Cruise Control (kinda low on the list of priorities).

tow/haul must go thru the BCM. Overdrive lockout goes through the BCM too. The tow/haul switch is connected to the BCM and then the BCM sends a class 2 data signal to the TCM to enable tow/haul mode. Same with overdrive lockout. Cruise control is independant; it is wired directly to the ECM

4. I suspect that APP has nothing to do with BCM, just ECU. Is this correct?

correct

think you would be better off in long run to convert vehicle to 12 vdc, normally bulbs. that would be easier than problems from 24vdc damaging dmax ecm and other components should you get short. if you have motors that run off 24vdc, you could setup batteries to put out 24vdc to them and 12vdc to vehicle.

I am investigating both options, but as of now I am indeed thinking 12 volt system due to space limitations for the 2nd alternator. Somehow I don't think I can fit the original 24 volt alternator (huge SOB with everything sealed, which was nice). Besides, with Duramax I can no longer disable the electrical system while running anyway :-(

2. What functionality of the instrument cluster is dependent on the BCM?
How much of the instrument cluster will operate with just ECU/TCM (speedo/tach/temp gauges?)

unfortuantly, nearly everything. The BCM controls the PMM (power mode master) functions, that is the data signal that turns the IPC on and off, etc... Im not sure if the IPC would even work without the BCM.


I thought there's a fall-back mode if the PMM fails (BCM is dead). I seem to recall it had something to do with having no PMM, but knowing the engine is running. I'll read up when I get home.

3. What drivetrain-related switches/control would be normally going through BCM? What should I consider replicating? E.g. Tow/Haul switch (I'm unclear whether there is one for Duromax/Allison and what it controls), O/D disable (again, not sure there was one in the first place), Cruise Control (kinda low on the list of priorities).

tow/haul must go thru the BCM. Overdrive lockout goes through the BCM too. The tow/haul switch is connected to the BCM and then the BCM sends a class 2 data signal to the TCM to enable tow/haul mode. Same with overdrive lockout.


Oh, bummer. I guess I will have to find a BCM after all. In the '02 books I haven't found anything about tow/haul switch for Allison (only 4L60-E I think) or O/D disable, but I'll look again at the BCM wiring diagrams.

Just going on the limb here, there wouldn't happen to be documentation on the class 2 serial interface out there? If there are specs on the messages they send, it would be absolutely awesome (then I can make my own BCM/DIC/etc. replacements).