jpk

I have a 2015 CD. I'm looking to connect a rally odometer for Time/Speed/Distance rallies. This is basically an odometer that can measure to the 1/1000 of a mile. I need to tap the vehicle speed signal, but from what I can tell, it's carried as a digital signal in the CAN bus. I need an analog pulse, either positive or negative voltage. Has anyone had any luck tapping the vehicle speed signal somewhere inside the vehicle?
I see that the individual wheel speed sensors feed into the PSM unit under the hood. I could possibly tap one of those, or put an external sensor reading a halfshaft, but I then have the issue of getting a wire inside the cabin.
I'd be grateful for any suggestions about tapping the VSS or feeding a wire into the cabin...

hotrod2448

Yeah, I'm sure it's CAN. I know Lingenfelter makes a CAN to analog converter for some GM products but, I wouldn't hold out hope that something like that exists for Porsche and even more so a Cayenne at that. You might be able to pull it out of the OBDII stream with something like this:

jpk

That Dakota interface is interesting - I'll have to dig into that a little deeper. Thanks!

garrett376

Feed a wire through the A/C drainage vent exit flange - it comes in below the dash on the passenger side and the flange is wide enough to poke through it and not affect the drain itself.

jpk

Thanks for the suggestions. I ended up ordering the Dakota Digital OBD2 interface. Should have it next week then I'll see how well it works. I'm a bit concerned about latency, and some have mentioned that when using this to drive a tachometer the response rate is not that good, but for my purposes, it should be OK.

RS-America

We tried tapping into the OBDII connector for accurate speed/distance. Could not get it to work consistently.
Elsewhere on renlist found a post that concluded that the amount the odo is off is not linear. Calculated 3mph plus 5%
Made a chart to the 10th and use it for TSD - our scores improved significantly.
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jpk

If needed, I can go with an external sensor pickup - there's a convenient spot to mount one into a threaded hole on the transmission where it can read off the front driveshaft coming out of the transfer case. I was just hoping for the easy way out.
I'll have a chance to run on some previously measured roads without being in competition, so I'll see how the OBDII interface works.

RS-America

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Hall effect sensor is the best -most accurate- way to go, we have not done this yet. Your approach is the same as what we and our tech decided on.
Be sure to hit the main shaft as those going to the wheels turn at different rates. Would like to see and hear about your hardware & install.
We also use an iPad that has GPS to run the app "GPS Rally Computer" just need to be sure what class to go into, probably equipped.
Richard Henrion from Ludington MI has entered his VW Toureg TDI into our RASC clubs ALCAN 5000 rally to be run in 2020.
Rainier Auto Sports Club and other local clubs have a full schedule. We also go to Canada for RallyBC events.
What club / rally do y'all run with?
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jpk

Detroit Region of the SCCA has a strong TSD rally program with 6 or so events annually. Neighboring regions provide an opportunity for another 6-8 rallies annually. Although I usually run stock class (more challenging...) I've put on "Pavement Ends" for the past few years, which is the primary reason I need the odometer. I just use an Alfa Club clock/odometer.
Past few vehicles have been GM trucks, and they have tap for the VSS output under the dash which has worked very well for me.
I'm working controls for the Son of Sno* Drift TSD rally next weekend, then a couple of weeks later, is the Sno* Drift stage rally in Northern Michigan where I'll be running sweep. Nice to have the odometer, but not a necessity. I'm sure the ODBII output will be fine for that, but I'll figure on installing the sensor at some point for accurate mileging for my rally.
I've found a good spot to mount the pickup on the Cayenne; on the left side of the transmission, toward the back is a 6mm threaded boss and the front driveshaft runs along side. Should be easy enough to mount the sensor and add a couple of magnets to the driveshaft.
If your trying to use GPS based measurement, I'd strongly suggest getting an external GPS receiver. I have an older bluetooth unit made by QSTARZ (model BT-Q818XT) which made a huge difference in accuracy - it sends position updates at 10Hz (10 times per second) which is far more often than most phones or tablets will do with internal GPS. As a bonus, you can place it in a position where it can get a solid signal, like in the back window.

jpk

I've hooked up the Dakota Digital box and chased down an odometer factor. The past three trips to work or home have shown < .7% difference compared to my handheld GPS ( 0.2 miles over ~30 mile trip) so it's working better than expected.
I'd say it's just as good as running off the VSS output connection on the GM trucks, which is good enough to measure a rally route.

hotrod2448

Glad it worked out.