VSS fluctuation while stationary

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Exidous
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VSS fluctuation while stationary

Post by Exidous »

Hi All,

First time post but I have my first question. It's not really critical so I figured I ask here rather than bug Matt.

Setup:
MS3Pro U 1.5.0 TS MS Ultra 3.0.28
94 RX7
Self Built harness (as a note, the shielded wire in the flying leads provided with the ECU are not grounded to anything. Neither are the TPS, CKP or front L/R abs sensors.)
SBE LS1 full Mamo top end
T-56 17 tooth reluctor
525lb inj @ 3 bar running 4 bar though

I have the T-56 VSS coming in on the CMP VR on my MS3PRO U. The Cam is on Dig Freq 2 inverted. While moving, the speedo is accurate within 1MPH @ 60MPH (GPS verified) with only the prelim data I entered. My issue is that the MPH jumps while the car is stationary. As soon as it registers 1MPH or more it's fine. Is there a filter setting somewhere or do I have to electrically filter with a cap or something?

The log is short but it seems the noise might be from the spark. MPH rise as I blip the throttle. But as soon as I start moving the needle is solid where it should be.

I'm also not getting anything on my Dash speedo(high current out 1). I'm guessing I just need a 1k pull up to 12v for that.
Exidous
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Re: VSS fluctuation while stationary

Post by Exidous »

Small update on getting the dash to work. A pull-up was a no go. The signal needs to cross ground (AC).
nathaninwa
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Re: VSS fluctuation while stationary

Post by nathaninwa »

The T56 had a vr sensor still correct? There was some discussion the other day about this and using a 10k ohm resistor across the 2 wires on the sensor should fix this problem
Volvo 940, 2jzge, MS3Pro, daily
240Z, 2JZ, MS3Pro boost control
Exidous
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Re: VSS fluctuation while stationary

Post by Exidous »

I'll give it a try, thanks.

It is a VR sensor.

Edit: no dice. I think the 10k was better but certainly not fixed. I'm going to play with the resistance to see if I can kill the noise but still allow the speedo to work at 1MPH.

I had also grounded the shielding but don't think it did anything.

A "squelch" setting would be nice too.

I've also added an sgi5e between the MS3 and my speedo. I have it set at a 1:1 ratio so it's just taking the pulse in and changing it to a sine wave. A very small cap (.01uf) was suggested my Matt but I didn't have one laying around. This way I can still have the MS3 do all the math since the sgi5e Cal steps can be a tad crude.
Exidous
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Re: VSS fluctuation while stationary

Post by Exidous »

Just an update. I used a 0-10k pot and ended up at about 900ohms. A far cry from 10k. If I went below 350ohms it started to affect very low speed resolution.
billr
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Re: VSS fluctuation while stationary

Post by billr »

Can you fit a Hall sensor in there? Sure you can, but may have to make up a "special" using an Allegro IC. I generally prefer VR, but "stationary" operation is not what they are intended for; this problem may keep coming back no matter how you fuss with it.
Exidous
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Re: VSS fluctuation while stationary

Post by Exidous »

A Hall sensor isn't necessary. I just had to find the right resistance balance between noise rejection and passing the signal. Ended up being about 600-900ohms.
64bit
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Re: VSS fluctuation while stationary

Post by 64bit »

nathaninwa wrote:The T56 had a vr sensor still correct? There was some discussion the other day about this and using a 10k ohm resistor across the 2 wires on the sensor should fix this problem
I have run into this same issue myself, and the 10k didn't work. I tried one to ground on both VR+ and VR- (not at the same time), I tried a 10k across the two, I moved my main ground all around the car... No dice.
Exidous wrote:Just an update. I used a 0-10k pot and ended up at about 900ohms. A far cry from 10k. If I went below 350ohms it started to affect very low speed resolution.
What is the wattage of that pot? I have a huge package of resistors that I can try, but really just looking for the simplest solution.

Having my 4R70W think the car is doing 150+ while I'm sitting still, is kinda a pain in the ass. I'd love to not be forced into manual shifting.
1994 Mustang Cobra
351w Turbo w/MS3 GoldBox xTra
4R70W Analog w/ Microsquirt TCU
Exidous
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Re: VSS fluctuation while stationary

Post by Exidous »

Even at higher speeds the wattage in the signal is relatively low. I have a 1K 1W resistor on there now but it's(resistance) not low enough. The pot was quite small as well, maybe 1/2-1W. I'll be picking up something in the 500-700 range tomorrow.
Exidous
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Re: VSS fluctuation while stationary

Post by Exidous »

Final setup:

vss from T-56 560ohm 1watt
Abs front driver/passenger 250ohm 1watt

I just wish there was a sensitivity setting on the vr modules in the Pro. I have traction control working although not strong enough and all speed sources are in agreement.

My rx7 uses one wire to signal the other to shielded ground. Seems to be really noisy but it all works now.

64bit, are you seeing 150mph only or does it fluctuate with say throttle input? I wantonly seeing 5-10mph based on RPM. How many Pulses Per Mile you are running could make the MS count be way off.
64bit
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Re: VSS fluctuation while stationary

Post by 64bit »

Exidous wrote:Final setup:

vss from T-56 560ohm 1watt
Abs front driver/passenger 250ohm 1watt

I just wish there was a sensitivity setting on the vr modules in the Pro. I have traction control working although not strong enough and all speed sources are in agreement.

My rx7 uses one wire to signal the other to shielded ground. Seems to be really noisy but it all works now.

64bit, are you seeing 150mph only or does it fluctuate with say throttle input? I wantonly seeing 5-10mph based on RPM. How many Pulses Per Mile you are running could make the MS count be way off.
So, this is in my 94 Cobra with a 4R70w auto on a Microsquirt trans controller.
When the car is moving faster than 4-5 mph, the speed reading is smooth and accurate. When I come to a stop, it'll run up anywhere between 40 and 140ish mph randomly. This causes the micro to start shifting gears. Eventually, it'll put me in OD, lock my converter... And stall the car. So until I find a solution, I have to manually downshift when I stop.

Check out the image below for reference.

Image
1994 Mustang Cobra
351w Turbo w/MS3 GoldBox xTra
4R70W Analog w/ Microsquirt TCU
Exidous
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Re: VSS fluctuation while stationary

Post by Exidous »

You just need to add a resistor like I did. Get a 10k pot and wire it across the two wires coming from the sensor on the trans. Start at 10k and lower the resistance until the noise is gone. Mine looked exactly the same.

The resistor will cause a voltage drop across the input. The drop will reduce/eliminate the noise. The noise is voltage. Speed is generally Pulse Per Mile. Mine would jump as high as 460MPH. It's just random.
goodysgotacuda
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Re: VSS fluctuation while stationary

Post by goodysgotacuda »

Following up to see if the ~560ohm seems to still be working for you?

my T56 Magnum has a noisy signal when stopped and cleans up well once rolling. I'd like to get my launch control working, but it's hard getting 40mph readings while stopped. :evil:

It'd be nice to configure launch to reference my front VSS(2)!
1972 Plymouth 'Cuda - 5.7L Hemi w/T56 Magnum

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64bit
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Re: VSS fluctuation while stationary

Post by 64bit »

Exidous wrote:You just need to add a resistor like I did. Get a 10k pot and wire it across the two wires coming from the sensor on the trans. Start at 10k and lower the resistance until the noise is gone. Mine looked exactly the same.

The resistor will cause a voltage drop across the input. The drop will reduce/eliminate the noise. The noise is voltage. Speed is generally Pulse Per Mile. Mine would jump as high as 460MPH. It's just random.
I tried my luck with a 10k, 4.7k, 3.3k, 2k, 1k, 680, and a few smaller resistors, not a single one of them cleaned up the issue. I ended up actually having a resistance low enough that the VSS no longer registered. I was frustrated and basically had given up on the system. I was going to install a Hall Effect ring and sensor on the yoke of my rear axle. Fast Forward a month or so... I installed the new (at the time) 1.0.2beta2 TCS firmware, and now all of my VSS fluctuations are completely gone.

Im still wondering if its a curcuit issue, or has something to do with the drastic change in ambient temp. So I guess I'll have to revisit it next spring/summer. :roll:
1994 Mustang Cobra
351w Turbo w/MS3 GoldBox xTra
4R70W Analog w/ Microsquirt TCU
goodysgotacuda
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Re: VSS fluctuation while stationary

Post by goodysgotacuda »

64bit wrote:
Exidous wrote:You just need to add a resistor like I did. Get a 10k pot and wire it across the two wires coming from the sensor on the trans. Start at 10k and lower the resistance until the noise is gone. Mine looked exactly the same.

The resistor will cause a voltage drop across the input. The drop will reduce/eliminate the noise. The noise is voltage. Speed is generally Pulse Per Mile. Mine would jump as high as 460MPH. It's just random.
I tried my luck with a 10k, 4.7k, 3.3k, 2k, 1k, 680, and a few smaller resistors, not a single one of them cleaned up the issue. I ended up actually having a resistance low enough that the VSS no longer registered. I was frustrated and basically had given up on the system. I was going to install a Hall Effect ring and sensor on the yoke of my rear axle. Fast Forward a month or so... I installed the new (at the time) 1.0.2beta2 TCS firmware, and now all of my VSS fluctuations are completely gone.

Im still wondering if its a curcuit issue, or has something to do with the drastic change in ambient temp. So I guess I'll have to revisit it next spring/summer. :roll:

TCS firmware?


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1972 Plymouth 'Cuda - 5.7L Hemi w/T56 Magnum

MS3 Gold Box, TunerStudio MS/MegaLogViewerHD user
64bit
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Re: VSS fluctuation while stationary

Post by 64bit »

goodysgotacuda wrote:

TCS firmware?
Nothing that pertains to your issue.
1994 Mustang Cobra
351w Turbo w/MS3 GoldBox xTra
4R70W Analog w/ Microsquirt TCU
jeffmarsh750
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Re: VSS fluctuation while stationary

Post by jeffmarsh750 »

If the alternator is good Motecs don't do this, makes me wonder if that's why we have so much trouble here with sync loss as well.
Fastest MS powered vehicle on the planet ! 6.60@208mph
goodysgotacuda
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Re: VSS fluctuation while stationary

Post by goodysgotacuda »

I've put in a dedicated shielded [grounded shield] wire to the VR output shaft sensor and still get quite a few mph worth of noise while stopped. Excellent signal while moving, I'm about to give up on it.
1972 Plymouth 'Cuda - 5.7L Hemi w/T56 Magnum

MS3 Gold Box, TunerStudio MS/MegaLogViewerHD user
Exidous
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Re: VSS fluctuation while stationary

Post by Exidous »

I had to take a break due to moving but I ended up at the lowest resistor I could and still have everything work once I started moving.

Grounding the shielded wire helped quite a bit as well.
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