Configuring a GM VSS for speedometer input

[928sg]

I'm using the VSS from a Corvette T56.  It's variable reluctance sensor with 17 pulses per revolution.  The config for speedometer on the Thunder shows examples for CAN wheel speed module or a hall effect speed transducer.  What is the best way to configure this?

in most cases this sensor is grounded on one lead and the other sends the pulses to the speedometer.

This is the first of many questions as a new owner of a Thunder ECU.

[cj]

From what I can see about factory tyre size & diff ratio, 17 pulse per rev on the output shaft is roughly equal to the "standard" 4000 pulse per mile used in a lot of vehicles. You should be able to read this on any DI - you dont even have to use the special high frequency ones on the thunder.

As you say, just 1 wire to ground (or sensor ground from the ECU), and the other to the ECU input. Pick any digital input and configure it as LR or RR wheel speed input. Set the calibration number to 235 to start with and see how accurate that is compared to a GPS.

This should be similar to the hall effect sample config except you dont have the 12/5v wire running to the sensor.

 

[Stevieturbo]

8 hours ago, 928sg said:

I'm using the VSS from a Corvette T56.  It's variable reluctance sensor with 17 pulses per revolution.  The config for speedometer on the Thunder shows examples for CAN wheel speed module or a hall effect speed transducer.  What is the best way to configure this?

in most cases this sensor is grounded on one lead and the other sends the pulses to the speedometer.

This is the first of many questions as a new owner of a Thunder ECU.

The GM sensor is a VR sensor, both wires should go to whatever device is reading as a sensor ground and signal. Not chassis ground as you are suggesting.. As to whether the Link can accept a VR signal, they would need to confirm.

[928sg]

I should have worded it better, Ground as in sensor ground through the ecu.  I stumbled across the GP speed input, after posting and it looks like that will work.  I don't want to tie it to the RR or LR input because I'm planning on using traction control.

[Stevieturbo]

As the gearbox VSS is basically a direct link to the driveshaft/propshaft, there isnt really any technical reason why that could not be used as a driven speed reference for traction control which would negate a need for two driven wheel speed sensors.

 

Either or though, whichever is handiest.

[cj]

6 hours ago, 928sg said:

I stumbled across the GP speed input

The problem with GP speed inputs is that they cant be assigned as driven/non driven wheel speed, so while you can log it etc and even pass it through to an output PWM signal to other devices in the car, the internal logic in the ECU wont treat it as a vehicle speed source - so things like idle control wont be aware of vehicle speed & the speed based lockouts wont work. Have a look in the Chassis -> speed sources section of the config. To get traction control to work you need to set a source for driven & non driven wheels, and your options are only combinations of the 4x wheel positions.

If you are planning to pull in per-wheel speeds in via ABS signals or something, you dont really need the gearbox speedo drive at all. If you are not planning to use ABS sensors, you need to think about how you are going to measure speed on a non-driven wheel as you need this for traction control

[928sg]

CJ,   Thanks for the heads up on the chassis speed  sources.

My project was originally planned for the following phases:

1.   Get the engine running, tuned and driveable

2.   Tab into the ABS for traction control

3.  Convert the factory cooling control to using the link ECU.

I was planning to convert T56 17 pulse per revolution to the Porsche 8 pulses per revolution signal with a Dakota digital signal converter but it was suggested here that the Thunder could do that.

I'm currently creating a spreadsheet to list all of the sensors, inputs and outputs so I'm still in the data gathering phase.

I'm pretty sure I'm foraging in new territory as far as the Link Thunder ECU goes.

Porsche 928, 6.5 liter stroker with ITB's, VAG COP, mixed with a Corvette T56 trans.   I know of another 928 stroker with ITB's running on a fury, but they aren't doing COP, traction control, or the T56. 

The more I learn about the Thunder ECU, the more it looks like this might be one huge project.

The advantage of the 928 is that the ECU mounting location is right next to the master electronics panel where every single electrical connection is termed.

[cj]

You shouldnt need to convert the speed pulses. The 17 pulse per rotation should be ~500mph when it maxes out the frequency limits on a DI which is probably enough.

Depending on how far apart these steps are in your calendar, you can either 

a) not worry about the gearbox speedo drive, just dont have a speedo for a bit then swap to using ABS inputs when you have them wired/configured. The ECU doesnt care where it got the signal from, as long as you can tell it at least 1x wheel speed it can be configured to work as vehicle speed etc. More wheel speeds just gives you more options. It doesnt strictly need a speedo input either, it just means you can have various settings change based on vehicle speed.

b) configure the gearbox based speedo as RL or RR wheel to start with so you have working speed input (and I assume pass through to vehicle speedo via an Aux out). Then once you wire in all the ABS wires, change this back to a GP speed input so it becomes just a data point but not used for anything. This way you wont have 2x speed inputs for the same wheel.

 

[928sg]

looks like I may use both.  Speed sensor from trans (simple and I like redundant systems) and I will look into tapping into the ABS sensors as i will need that for idle control.   Later 928's use one of the front abs sensors for speedometer, so I need to look at the car schematics to determine the differences.

[928sg]

On 9/1/2019 at 6:17 PM, cj said:

You shouldn't need to convert the speed pulses. The 17 pulse per rotation should be ~500mph when it maxes out the frequency limits on a DI which is probably enough.

That leads me to a question about the ABS sensors and using those as a DI.   My abs hubs have 45 teeth.  I looked at some of the other threads that mentioned exceeding the frequency capabilities on digital inputs.

 

 

 

[cj]

From the help file

 

Most of what people are talking about is the ~500Hz limit on the non-thunder models. In reality these allow a fair bit over 500Hz (maybe a few hundred higher depending on model + other input confgs), but they start reading 0 if you exceed 500Hz by too much. The thunder can accept 6.5Khz on DI11-16, which means with a 45 tooth ABS wheel & a 285/35 R19 tyre, you will be doing ~1000kph to max out the frequency input.  So as long as you wire the ABS sensors to the high numbered DI's on your thunder, you'll be fine.

[928sg]

CJ, Thanks again for the info.  I saw the info in the help file, I don't know enough about the frequency generated per pulse and could not find any tables (that I could read). I found some good info on the MS support forums.   I did notice that the 11-16 DI's were set up for the LF, LR, RF, RR in several of the samples, and now I know why.    I literally sat down on the floor with my A & B harnesses in the living room, so I could familiarize myself with the pin outs.  I also started a spreadsheet similar to the installer I/O table, but also adding a column for the harness and the notes.   Building the spreadsheet, going through the help, as well as the assistance here has provided me with the confidence to really get down to the wiring.    I always like to give back to communities like this so I'm collecting all of my info so that after I'm up and running I can start a wiring 101 thread to outline what I've learned to share for others if they would like, including my spreadsheet.  Like everything else I jump into the deep end of the pool.