VSS Setup (and tuning)...

944 V8 (LTX / LSX) VSS Setup

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Stock sensor (GM part # 15547452), shown with pigtail connector (GM # 12085498, or AC Delco #PT120)
Also, GM #2131701 / 24225896 (1999-02 Camaro) Speed Sensor may be used.

The vehicle-speed-sensor (GM part #15547452) shown is used on transfer cases of 1989 and newer S-10 truck, AWD Astro Vans, and 1987 and newer full-size 4X4 trucks.

40 Tooth Reluctor Ring

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Stock cam gear from a 944 (40 Tooth)

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VSS Setup using the 944 Cam Gear and GM #2131701 / 24225896 (1999-02 Camaro) Speed Sensor

VSS Tuning info

Posted by dawgz83944 on Mon Jun 05, 2006 10:10 pm

"If you are trying to tune VSS, this gets you accurate readings.

1. Calculate the Revolutions per Mile (Using Tuner C.A.T.S or whatever) Mine on 225 50 16 = 838
2. Take the 838 X 1 (Rear end ratio) X 40 (Number of teeth on reluctor)
3. It gave me 33520 take this number and divide it by 4000 which gave me 8.38 so in Speedometerscaler enter 8 (no decimals)
4. Take the 33520 and divide it by the scaler so 33520/8 = 4190 then take 4000 and divide by 4190 = .954 (My case)
5. Speedometer scaler multiplier = .954
6. For the Speedometer scaler take the tire revolutions per mile and divide by 60

838/60 = 13.97

If you use a program like Tuner CATS that auto calculates, it creates a psychotic number like 103.?? ms for time between pulses for stop (or something like that) this number should be ~34ms. What'll happen if you leave it at 103ms is you'll be stopped at a light and the IAC won't close for a 3-4 seconds idling at 1200rpm, which won't help your smog chances in California.

Mine reads perfectly with the speedo in the Porsche. BTW, the reason the rear end ratio is 1:1 is because the GM VSS is on the output shaft whereas the RH setup goes after the transaxle, and should not take into consideration any rear end ratio."

Sweet! A crafty devil aint ya!

dawgz83944 and marc a get the credit for the VSS info...

...crafty devil

Yea...crafty, sneaky...I've been called a LOT.

Hey Greg,

So that truck sensor looks like a better fit for picking up off the stock ABS reluctor. Is it compatible with the LS1 computer? If so, I may rethink using the Camaro part on the rear ABS reluctor, and go with the front one. My car doesn't have ABS, but the 968 front spindles have the reluctor. I was going to use my donor's car rear reluctor to pick up the signal for VSS. In another post, another time, I posted that the Camaro VSS sensor could easily mount in the rear trailiing arm. This has me very intrigued, and I'll end up with yet another part I bought that I won't use. I have HPTuners, so using the Porsche 45 tooth reluctor is no problem, and long as I can get the VSS sensor mounted up.

87-944S wrote:...So that truck sensor looks like a better fit for picking up off the stock ABS reluctor. Is it compatible with the LS1 computer?

S10 guys are using it...
The vehicle-speed-sensor (GM part #15547452) shown is used on transfer cases in 1989 and newer S10 truck, AWD Astro Vans, and 1987 and newer full-size 4X4 trucks.

With HPTuners, you should be able to specify any # of speed pulses, from (ex.) 4000 to 8000. Output voltage of the sensor is variable, based on PPM (Pulse Per Mile).

BUT...
With a manual transmission, it doesn't matter where the speed sensor is located OR the # of pulses, as long as the PCM knows the vehicle is moving. Also, you need to know # of pulses and tire size/gear ratio when programming.

SUMMARY:
The LSX PCM VSS wire supplies a 4000 pulse per mile signal, but can be reprogrammed for any sensor.
Therefor, any GM VSS sensor will work with the LSX PCM.

Is there not already a sensor in the transaxle? Is there anyway of converting that signal to the correct VSS signal? I'd prefer a bit more electrical work than having to add another sensor with a toothed wheel.

..........

The 45 tooth ABS reluctor (@ the front hub) is another possibility.
ABS was offered as an option from 1987 on...
1988 - '89 Turbo S had ABS standard...

robstah wrote:Is there not already a sensor in the transaxle?

Yes there is an impulse sender on 85.5 and up 944's, all 951's and 87+S/S2's.
IIRC it is a 2 pluse per revolution. I don't know what its voltage is or the wave type. I am adding VSS to my car, I will look at the stock porsche sensor revolutions etc.....

The sensor was $28.99 from Autozone, $45 from Advanced, so I placed an order with Autozone, there are no Autozones nearby. I'll post any pics etc, if I can get it to fit.

948 wrote:

robstah wrote:Is there not already a sensor in the transaxle?

Yes there is an impulse sender on 85.5 and up 944's, all 951's and 87+S/S2's.
IIRC it is a 2 pulse per revolution. I don't know what its voltage is or the wave type. I am adding VSS to my car, I will look at the stock Porsche sensor revolutions etc.....

[sigh...]

Yea, used for speedo...
"gear-driven" (not cable) is what I should have said...

BUT, if you can specify 2 PPR [converted to PPM...] in the PCM tuning, no problem.

Paul,
What does 2 PPR convert to as PPM [Pulse Per Mile] ?

Mike,
What are the PPM limitations in HPTuners?

PET...

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17...088.409.197 / Speedometer Pinion
18...014.409.193.A / Bush
19...944.606.210.00 / Pulse Sender
- ...016.409.187 / Speedometer Pinion Drive Wheel

DC Auto...

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gt1scca wrote:Paul,
What does 2 PPR convert to as PPM [Pulse Per Mile] ?

I checked on a spare 5P I have; 2 revolutions of the sender is a little more than 1 revolution of the drive flanges. So, assuming the sender is 2 PPR, it would be ~3249+ pulses per mile.

OK, I wanted to post a screenshot of the VSS tab of HPTuners, but I am definitely image posting challenged on this board. A little help?

87-944S wrote:OK, I wanted to post a screenshot of the VSS tab of HPTuners, but I am definitely image posting challenged on this board. A little help?

Check this out, Mike.

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The "HELP" section of this board is another forum...no FAQs like PHB, so I have become the help section. If you still need help, let me know. Heck, email 'em to me, I'll put them in-post for ya! (JK)

The buttons take some getting used to.
I didn't get it @ first myself...

Will the DRAC module do anything for us?

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Here's where I changed the final drive ration to 1, changed the tire size to 24 and pulses per revolution to 45, like the ABS reluctor. I just recalulates the appropriate values.

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Correction, I meant tire size to 25.

If you do not have a spare 944 cam gear laying around, you can use a chain sprocket gear from McMaster-Carr. The 40 tooth version is available from McMaster.com, part no. 2299k318, and it only costs $10.59 ! It will be necessary to open up the internal diameter, drill the six mounting holes, and then split it in half so that it can be easily mounted on the transaxle half-shaft.

To supplement my previous post, attached are the drawings that specify the modifications necessary for the McMaster-Carr part and for making a sensor bracket. The reluctor wheel design fit the axle with only a little grinding on the internal diameter to better fit around the half-shaft. The sensor bracket will require customization based on your particular sensor/transaxle combination. Hope that this information can help someone.

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I am not sure if I would use that gear from McMaster. I would worry about how the sensor picked up the teeth, knowing how their cut differently from say a cam or any other sensor based gear.

Is it to be set up like this? [You must be registered and logged in to see this image.]

robstah wrote:I am not sure if I would use that gear from McMaster. I would worry about how the sensor picked up the teeth, knowing how their cut differently from say a cam or any other sensor based gear.

I don't think the tooth shape will matter. The sensor is an inductive pick up and it is only looking for a change in inductance which through the circuitry is then changed into a high/low signal. Whether the input waveform is square or sinusoidal does not matter.

I thought the PCD of the 944 cv's were 86mm but was never sure.
Hey Bridar, Does that 3.17" dimension go over the cv axle step? Like the one in Marc A's Pic of his setup?
Nice post here BTW.
If you have trouble picking up the signal, the sprocket can be put in a lathe and the tips can be trimmed to 1/8" flats, That will solve the pickup problem if there were any. You could move the sensor down towards the new flattened pick-up teeth....JAT

I did have to grind the PCD dimension slightly to make it fit properly. But after fit-up I revised the drawing to show what I believe to be a workable number. Some hand grinding may be required, but it shouldn't take much. Also--My car is a 968. I believe the axles are the same as a 944 but I am not entirely sure. It would be best to verify the dimensions if you can (but at $10 a sprocket, you can't loose too much).

Good point about milling the tips of the teeth, although it willl be difficult to hold it in a lathe once it has been slit in two. You could always buy another blank sprocket and mill the teeth before slitting.