Wiring speedo to Link - a few questions

[M1tch]

Hi all,

Currently my stock ECU is running the instrument cluster (as well as a few other functions), I am looking to swap out my wheels and tyres so might need to adjust my speedo to correct for the different size, there is only 1 speed signal that comes into the ecu (Link is reading this as DI#1) and is at 1hz per 1mph. The Link itself isn't connected to the instrument cluster at all it seems meaning that any correction on the Link won't affect the instrument cluster so I am looking at how I could get the Link to run the cluster.

My guess is that I could just use the stock wiring loom and use a digital output to the speedo on the instrument cluster instead of the stock ECU running it? I am thinking that if the rest of the cluster is powered and everything else is run on the stock ECU the cluster would just need the speed signal fed through. I have the pin outs for the stock ECU somewhere, guessing I can just configure one of the digital outs to send the signal adjusted on the Link? I can see the tach input and output but can only see a speed signal coming in and there seems to be a data line going to the instrument. I guess I would need to check the signals at the back of the instrument to work out which one is the speed in at that end?

I know that the stock ECU is running the instrument cluster as I have set the Link ECU to sweep the rev counter on start up (which it doesn't).

I am guessing that instead of trying to find a speedo out signal I could feed the speed in signal into the link into DI#1 as it is at the moment and then output it via another DI and feed that output into the input on the stock ECU meaning that the Link can adjust the speed signal before it gets to the ECU to then be sent to the cluster.

Thanks in advance!

[cj]

Which car are you working on? A lot of the earlier japanese stuff ran gearbox -> speedo then speedo out -> all other systems that want a VSS signal. 

you'll need the factory wiring diagram to figure out where the signal goes once it leaves the gearbox (assuming its not canbus - at which point it comes from ABS). If its old enough to be a mechanical speedo drive its another story. In theory you want to change the wiring so the link is the first point of contact with the speed signal, do any modification, then have another output on the link to output the new speed signal and have this continue on through the rest of the factory "path" so other computers/gauges all get the modified speed signal

[M1tch]

15 hours ago, cj said:

Which car are you working on? A lot of the earlier japanese stuff ran gearbox -> speedo then speedo out -> all other systems that want a VSS signal. 

you'll need the factory wiring diagram to figure out where the signal goes once it leaves the gearbox (assuming its not canbus - at which point it comes from ABS). If its old enough to be a mechanical speedo drive its another story. In theory you want to change the wiring so the link is the first point of contact with the speed signal, do any modification, then have another output on the link to output the new speed signal and have this continue on through the rest of the factory "path" so other computers/gauges all get the modified speed signal

Hi there,

Its a Toyota MR2 roadster (mk3), it does use a Canbus, reading further here is the current setup:

ABS sensors > ABS ECU > ECU (1hz = 1mph)  > Instrument cluster

The speed signal is being intercepted by the Link, I think I came to the same conclusion as yourself with where the speed needs to be intercepted, I was initially thinking:

ABS sensors > ABS ECU > ECU (1hz = 1mph) > Link ECU > Instrument cluster

However to your point it would make sense to intercept it before it gets to the ECU so:

ABS sensors > ABS ECU > Link > ECU (1hz = 1mph) > Instrument cluster

I think to make it work I just need to feed an output from the Link to the input on the ECU for the speed signal - should be as easy as simply cutting the original feed into the ECU and repinning the connector to take the output from the Link - basically feeding the stock ECU an adjusted signal.

I had a look at the link yesterday, I selected a spare digital output and set it to 'speed out', how do I configure the Link to take the input and send the adjusted output to the output? I can see the configuration for the speedo adjustment in the settings - does it automatically use this figure as I have set the digital out as a speedo out in the function list drop down?

I will at some point need to tap directly into the ABS ECU for signals to enable traction control, but that's a bit further down the road!

[cj]

8 hours ago, M1tch said:

ABS sensors > ABS ECU > Link > ECU (1hz = 1mph) > Instrument cluster

This sounds like the way to do it. Logically you cut the wire from abs -> factory ECU, and put the link in the middle of that cut wire. (DI as input, aux out as output).

You define a DI as LR wheel speed, and set the calibration number. Adjust this number until the speed shown in link matches the gps on your phone.

Grab an aux out and configure it as "speedo out" - I think this has to be one of aux 1-4 but will depend on the expected frequencies. Not all aux outputs can PWM signals at a high enough frequency. Once you set this, another option will pop up under the aux outputs "folder" named Speedo Out. Click on this and you can set the source DI you are "copying" as well as multiplier + offset values to adjust the frequency. Note that these multiplier values dont take any notice of the calibration for the DI - its just frequency in -> frequnecy out (with multiplier)

 

 

[M1tch]

9 hours ago, cj said:

This sounds like the way to do it. Logically you cut the wire from abs -> factory ECU, and put the link in the middle of that cut wire. (DI as input, aux out as output).

You define a DI as LR wheel speed, and set the calibration number. Adjust this number until the speed shown in link matches the gps on your phone.

Grab an aux out and configure it as "speedo out" - I think this has to be one of aux 1-4 but will depend on the expected frequencies. Not all aux outputs can PWM signals at a high enough frequency. Once you set this, another option will pop up under the aux outputs "folder" named Speedo Out. Click on this and you can set the source DI you are "copying" as well as multiplier + offset values to adjust the frequency. Note that these multiplier values dont take any notice of the calibration for the DI - its just frequency in -> frequnecy out (with multiplier)

 

 

I have DI#1 set as the speedo in from the OEM loom from the ABS and the calibration number I have works, I have grabbed a DI output and its set to be 'speedo out', there is a folder further down which has the speedo correction figure (percentage or offset etc) - am I correct to say that it will automatically use the DI Speedo out as the output or is there somewhere I need to configure the ECU to tell it what output to use?

[Link2ThePast]

Any update on this? I also have a mk3 MR2 and want to have a speed input into my g4x for launch control. (Maybe traction control?)

But I'm confused as to the actual process that the signal goes through. I was looking at the wiring diagrams and thought it went:

ABS sensors -> ABS ECU -> Speedo -> ECU (LINK)

Also in G4X, in "speed sources", It looks like I need to have a separate sensor for each wheel but the stock harness only has the one wire for a speed sensor input going into the stock ecu.

To avoid having to wire in separate sensors and adding in a voltage divider(? I can't remember what it is called), would I use that one wire, put it in GP Speed 1 and then calibrate it?

Would I then be able to set that same GP speed 1 input as FR FL RR RL wheel speeds?

If the above were true, in "setup" of "speed sources", I could use either driven or driving wheel speed source and not need both correct? 

Would this be a problem for launch control if I were to break traction?

 

[Adamw]

A single wheel or gearbox speed sensor is fine for launch control (a non driven wheel is better).  You will just need to assign your speed sensor as non-driven (G4+) or driven (G4X) for it  to work.   

For traction control you generally need all 4 wheels.

[Link2ThePast]

The thing is that for the MK3, the gearbox doesn't have a speed sensor and as far as I know that comes from  the ABS ecu. 

I haven't found a post yet determining what exactly the signal is. Is there a good way to measure that so I can use it for the link?

It is not clear whether it is driven or undriven wheel speed. Could I assign it as either one in PC link?

[Adamw]

If its the same signal that drives the speedo then it will be driven wheel (Called Driving in G4X).  Yes you can assign the same source to either or both driven/non driven.

[Link2ThePast]

If it is the same one, and comes from the speedo, does that mean it is already filtered and I do not need the pull up resistor? 

I was messing with it yesterday to try and get a signal and got a reading for a quick second before it went to 0. To be honest I'm not sure what I did to get it...

[Adamw]

Unknown, it could be anything.  

[Link2ThePast]

Lol dang. I'll keep messing with it