TOD discussion

[Ldub]

Bob M,
YOU DA MAN...wish I had the tech. abilities reqd. to figure something this complex out in the first place. Seriuosly, your aside for the non elec. eng. prone was too deep for me.
However, if you get a handle on this thing & produce a few "plug & play" units (harness, controller, DETAILED instructions, etc.) You can count me in as your first customer.

Hope ya get it to work, Ldub

[mbeach]

I couldn't open the Terracan links, but I have been suspecting the same thing (PWM signal) for a couple of weeks.

I have plenty of snow for practice, what wire(s) should I monitor?
I think that a few inputs would be in order (front axle, rear axle, ABS, 4Lo) to the TOD ecu.
I'd definately monitor the TOD to clutch solenoid as well.

I figure that this weekend I could get started checking voltages and frequencies under various conditions. It will be difficult to catch a 70/30 or an 85/15 condition however. It seems that TOD is all-or-nothing on ice and snow.

I'll think about a nice spreadsheet for gathering all of this data.

If we get the right information together, I have an extensive inventory of tools and parts to make this happen.
Heck, if it works I might not sell the VX after all.

[mbeach]

I was discussing this with my lead tech (super genius).

We can make this happen, BUT:
I need a TOD computer. They pop up on eBay all the time, except for today. I will pay up to $100 for one, I cannot use of of mine right now (too much ice on the road still).

We were thinking about catching the signal INSIDE of the TOD computer, before it hits the amplifier section. This should eliminate the need for a dummy load. We can make a PWM generator with a timer (555?). By altering the control voltage into the timer, we should be able to modify the square wave output. This means a KNOB, with infinite variability or presets (whichever you want).

HELP ME FIND A COMPUTER!!!

[bobmumgaard]

mbeach-
I imagine you have the snow up there to try this, I fortunatly haven't got the white stuff down here NE yet.

If you want to monitor what the TOD ecu is doing I think monitoring these wires would be the most important:

1.

TOD to Solenoid - On a 2000 it is the light blue wire that exits the TOD ecu from pin 4
If you hook a multimeter to this wire and monitor voltage it should hover around 0-1V most of the time and jump when the TOD dislpay shows power to the front wheels. An ocsiloscope would confirm if this is indeed a PWM signal.

2.

Front and Rear vehicle speed sensors- On a 2000 TOD ECU the front is pin 24 (green/white or grey/white), the rear is pin 23 (green/yellow or grey/yellow) and the reference for these sensors is pin 15 (green or grey)
The TOD ecu's logic probably looks at a differential between these two sensors and then decides how much torque split to enact. We could probably gain alot of insight on the function of the ecu by doing the same thing. I assume these two are probably PWM signals as well. If you use an oscilloscope with two channels of imput you can see this PWM differential occur when the rears slip.

If you want to look at the circuit diagrams yourself you can use Tone's maintaintence cd (if you don't have one just e-mail him or post and I'm sure he'll hook you up) The most useful pages are:

Driveline/axle > Driveline control (TOD) > Basic diagnostics flow chart > Checking failed pin > Connector pin assignment
and
Body and acceserories > Wiring diagram > circuit diagram 19 (the second 19)

I agree, at this stage a spreadsheet would be very helpful here, the way I'd set it up is with columns for this data:

Front speed sensor duty cycle
Rear speed sensor duty cycle
TOD-solenoid duty cycle
TOD-solenoid rms Voltage
What the solenoid is doing (0 front, 50/50 etc.)

Alright, so after we get this information together (hopefully it will confirm what the Terracan guys have discovered) it is a matter of making the modifications

I talked to a few of my EE collegues and they all agreed that substituting our own controlled PWM signal to the clutch instead of the ECU's signal would be the best route. This could certainly be done with a 555 like your tech said and it would be fairly inexpensive. Though I personally don't have the indepth know-how to build the actual circuit, but I know people that do, and you sound like you might have the knowlege and tools.

After thinking about the actual mechanics of modifying this system I think we have three basic options:

1. Modify the signals coming into the TOD ecu
This basically tricks the TOD ecu into thinking the car is doing one thing, and we get the desired result from the TOD ecu outputs. So if we modify the front or rear speed sensor signals before the ecu, then the ecu thinks there is slipping and we get lock-up. The trooper guys have kinda done this by cutting the front sensor wires. Then the ecu sends power to the front axle, but also throws a code. This method would produce the correct dash display. Though it scares me because if something goes wrong the TOD ecu would get fried....$$$

2. Modify the action inside the TOD ecu
I think this is the approach you and your tech are talking about. It would be the most elegant because it would all be contained inside the existing black box. If you can score an extra TOD ecu it could be taken apart and investigated, reprogramed almost. However, this approach would be hard to duplicate for the electronically timid among the VX community. Though it seems to be the most technically interesting.

3. Modify the TOD ecu's outputs
This would consist of modifying the signal from the TOD ecu to the clutch like I mentioned before. It is not the most elegant because it wont display correctly on the dash display but it would be the least risky and easiest to duplicate. The risk is minimized because you couldn't hurt the ecu (since the modification is after the ecu, you would need a dummy load though), and the soleniod is probably robust enough to withstand any minor malfunction we casue. The electronic circuits could be contained in a project box that would require cutting only the wire going from the TOD ecu to the solenoid. This makes it easy to install and produce for members on this board (might as well spread the wealth ehhh), you would have to cut one wire, install the knob, hook up power and ground and you'd be set. I think this approach is the one I'll persue.

Well thats my take on the whole deal right now, throw back your opinions on it and we'll keep brainstorming, this shouldn't be that hard. Plus, once the research is done and the modification tested there are plenty of guys on this board that could benefit from the knowlege obtained.

[mbeach]

My initial idea was option 1. I liked the fact that the display would be correct. However, once the vehicle were stopped, the TOD would be thrown into confusion. So I abandoned it.

Option 2 is the most elegant, yet it is not reversable (easily), removable, or easily installed. I'm going to try to veer from this, but we'll see. My goal is to have a correct dash display, and 5 modes of operation: Auto, 2wd, 15, 30, 4hi. All selectable with a knob. I think that by keeping it simple (5 modes, or outputs rather than infinite) I can make the display work as well.

I would need to:
a) turn off the AUTO display when the knob is switched to any other position.
b) turn on the appropriate lights with each mode.
c) default to AUTO mode whenever 4Lo is activated -or maybe not. 2Lo is an interesting option, if it's even possible.

I guess that I'm looking at option 2.5. I want to be "inside" the TOD computer for the display benefits, but I want it to be accessable and easy for a novice to hook up.

I pick up a better (portable) scope this week. This weekend I'm going to pull the harness(s) off of the TOD computer and make extensions (to minimize my crawling under the seat) that I can easily tap in to. I have the workshop CD, I'll be looking it over tonight. I think that I have a few spare connectors around the shop.

[VehiGAZ]

I really appreciate this conversation, guys!

I want only one thing - to have a switch to flip to go into 50%/50% (4WD Hi) mode, which would be best on snowy roads when going into 4WD Low is overkill, while leaving it in Auto ToD mode means it is CONSTNATLY (and annoyingly) engaging and disengaging the front wheels.

I figure I can use a light-up switch to indicate that it's in the forced 4WD Hi mode. That means I should go with option 3, but without the multi-position selector.

So circuit-wise, my switch would be put a dummy load on the output to the ToD, correct? Any advice on how exactly to wire it, and what to put on the "alternate" circuit?

Lastly, I may have that extra ToD ECU you are looking for, mbeach. I will PM you.

[VehiGAZ]

mbeach, your PM box is full. I sent you an e-mail to your yahoo address instead.