Anyone using VSS and cruise control? Got signal noise? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 03-22-2015, 04:27 PM   #1
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Default Anyone using VSS and cruise control? Got signal noise?

Anyone using/logging VSS successfully on car with cruise control?

I hooked up the VSS on my '97 and the result was not quite what I had expected. Initially, I had the VSS, OBD2, and cruise control module all hooked up in parallel (basically just tapped into 1M GRN-RED). The OBD2 and cruise control module behave as per usual (signal seems stable, cruise is steady when engaged), but the MS3 signal however has frequent spikes in the signal where the calculated speed jumps up substantially for one event.

I tried a few different things to isolate/eliminate the noise:
At first suspecting that I was getting a weak pullup voltage for the signal, I disconnected the OBD and went to attach a 5v pullup for the MS3. I discovered that the MS3pro was already configured with a clean pullup on the circuit I was using anyhow (oops!), but the result was still unchanged. So then I disconnected the cruise control module (with OBD2 already disconnected) so that only the MS3 was hooked up to the VSS. Now I get a clean signal that matches the calibration numbers as it should.


Next I reconnect the OBD2, so that the MS3 and OBD2 are both hooked up. Signal is still clean and good. Hook up the cruise control module again and the noise is back. So the cruise control module is definitely the cause of the signal noise.

Now, how to remedy the situation? My first thought was to use the MS3's VSS output to drive the cruise control. This kept the VSS signal clean, but the cruise control surged something terrible because of the lag time between input-calculation-output on the MS3. My next idea was to use the RSW terminal on the instrument cluster but to isolate it from the OBD2+CCmodule by cutting the trace and soldering a diode inline on the instrument cluster. I successfully modified the instrument cluster, hooked it all up, and... still getting noise on the MS3 VSS.

So, anyone got any ideas? How/why does the cruise control module create noise on the circuit? Any other ideas on how I can clean up the signal for the MS3 without sacrificing the cruise control?

* I've attached a log file that shows the VSS signal while "traveling" at about 34-35 mph. It starts with the cruise module disconnected and then again with it re-connected. The car was up in the air on jack stands, so you may notice that the load values are very low, but really it's just the VSS signal that I'm curious about.
Attached Files
File Type: msl 2015-03-22_12.29.11.msl (1.54 MB, 37 views)
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Old 03-26-2015, 02:25 PM   #2
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I have cruse control and just connected my VSS to my MS2 and have spikes... let me disconnect it and see if that gets rid of the noise on mine... I get spikes where it says i am doing 48 and 218 mph
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Old 03-26-2015, 10:55 PM   #3
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no go, disconnected CC module and still have noise on mine. I also only get the noise above 10 mph

Last edited by Dlaitini; 03-27-2015 at 04:48 PM.
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Old 03-29-2015, 10:10 PM   #4
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Does it look identical to the spikes in my log? What settings are you using?
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Old 10-01-2017, 07:56 PM   #5
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Did you ever find a solution? I fitted a reed switch from a cruise control car's instrument cluster to the speedo of my EUDM MX-5 (no cruise control etc), installed a pull-up and ran a designated wire to my MS3-PRO. It's working. However I do have some noise in the signal. It's annoying since I want to used the boost-by-gear feature

is it a matter of lack of shielding?
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Old 10-02-2017, 12:43 AM   #6
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I haven't yet sorted out a solution for this (aside from disconnecting the cruise control module and living without cruise control), but I do have a couple of ideas that I haven't had time to look into yet: (1) Years ago I replaced the NA cruise switch with one from an NB, and it's possible that the way it works (either on or off, as opposed to a "latching" relay) may somehow allow the noise. (2) Switching to an NB cluster and electronic VSS rather than the cable and reed switch of the NA. I've got all the parts and diagrams to do this, just haven't bothered to actually make the swap yet.

Unfortunately, these things probably won't help in your case since it isn't the cruise control module causing your noise. A lack of shielding may be letting it pick up noise. Depending on what your noise looks like, it is also possible that the cable itself is "sticking" and not giving a smooth reading or even the reed switch might be worn and giving odd readings?
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Old 10-03-2017, 12:53 PM   #7
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I've been running vss and cruise control on my NB and only rarely see a small 5mph jump in speed once in a rare while. Could be the NB sensor is just quitter than the NA setup.

Another although nuclear option is to run an ABS spindle and wheel speed sensor. Run the signal through a GM 4 pin ignition module to convert the signal to square wave and use that for your MS.
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Old 10-03-2017, 01:47 PM   #8
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My '99 speed signal is noisy. Perhaps same reason? Thus I have not considered boost by gear. If I were to try it though, I would find out how to use blend tables and % for gear, rather than absolute target. If you are interested in that, Eunos91, Bronson could explain how to do it. I don't know how to do it, but he does.
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Old 10-03-2017, 05:45 PM   #9
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well I need to confirm whether the fluctuations throw the gear calculator off (MS compares RPM vs. VSS to calculate the gear). I guess it wont do anything, so maybe i should just call it a day. At least launch control / flat foot shifting activation through VSS does work.

Adding an ABS sensor is no option though. Too much trabajo.
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Old 10-08-2017, 10:54 AM   #10
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Quote:
Originally Posted by Bronson M View Post
Another although nuclear option is to run an ABS spindle and wheel speed sensor. Run the signal through a GM 4 pin ignition module to convert the signal to square wave and use that for your MS.
Bronson, could you provide more details on this approach? I've got my 91 car prepped to use ABS sensors but haven't yet picked up any hardware or done any wiring to make use of them yet. If I could grab an off-the-shelf item to convert the signal, that sounds preferable to building an expansion board.
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Old 10-08-2017, 01:12 PM   #11
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Sure, this link should get into the details.

https://www.rx7club.com/adaptronic-e...1038431/page2/
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Old 10-09-2017, 12:17 PM   #12
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Thanks! Looks like that might be worth a try.
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