Can speedometer be reprogramed with tunerpro?
I have tried to change 4000 pulses/mile but it only changes
speed that ECM see, not LCD display reading.

What is this used for?

 

If I understand you right, the ECM/PCM sees what is programmed into it to correct the speedo display to tire size. The wheel sensors see how many turns the wheel makes and this is read by the ECM/PCM and the two numbers calibrate the display for tire size used.

 

Stock setting in VSS setup is 4006.96 pulses per mile.
I have tried to play with that nr. but it didn't change speedo
reading on LCD, it only changed TC lockup points and other stuff
related to vehicle speed.

So I'm wondering if there is any other way to change what LCD
speedo is reading. I've compared LCD speedo with GPS and it
looks like I'm ~3% off.
I know that it's not much, but I'd like to correct that if it's possible
with changes in EPROM.

 

If you have TunerPro, you would have to have the module that lets you read or change the chip in real time, or burn a new chip to make the corrections. I see that you have a '90 model, so you would have to have the right definitioin file for that model.

Mine is a '94 and uses the $EE definition file, so it can be changed with TunerPro, but not while it is running. Following is what the Help file says for the $EE definition file on mine:
----------------------------------------
Constants Table

Speedometer Calibration Values
Speedometer Scalar

Speedometer Scalar, Fraction

These two values provide the calibration factors for the speedometer. The Speedometer Scalar and the Speedometer Scalar Multiplier can be calculated as follows:

1. Calculate the number of speed pulses per mile (PPM) as follows:

PPM = Tire revs per mile X Rear End Ratio X Sensor Pulses

The Sensor Pulses value is 40 for an automatic, 17 for a manual F or B car and 2 for a manual Y-Car).

2. Divide the resulting PPM value by 4000. The Speedometer Scalar value is the resulting value rounded to the nearest integer.

3. Divide the PPM value by the Speedometer Scalar (integer) value calculated above.

4. To calculate the Speedometer Scalar Multiplier value, divide 4000 by the number obtained in step 3.

For example a stock 95 SS car with P255/50/ZR17 tires and a 3.08 rear end would yield the following values:

PPM = 760 x 3.08 * 40 = 93632

93632/4000 = 23.408

Speedometer Scalar = 23

93632/23 = 4070.957

Speedometer Scalar Multiplier = 4000/4070.957 = .983

Note that there is in fact more than one set of values that will work. In the above example you could also use a value of 24 for the Speedometer Scalar in which case the resulting Speedometer Scalar Multiplier would be 1.025.

 

Your profile mentions a '90 car. Is this correct?

Speedometer correction in a '90 needs to be done with the VSS gear ratio with the speedometer drive and driven gears. Post your rear axle ratio and rear "rolling" tire diameter. You will also need to determine the number of teeth on your drive gear on the output shaft of the transmission and the number of teeth on the driven attached to the VSS. After you've got all of the "knowns" math can determine the changes that are required.
The "rolling" diameter is the important "known here". You can mark the tire and floor then roll the car one "loaded" tire revolution and measure for circumference then do the math for diameter. You can also use the RPM advertised by the tire manufacturer for the math. The RPM advertised by manufacturer will vary. Not all RPM for a particular tire size are the same! RPM = revolutions per mile!

Here's a link to 4L60 info complete with the formula and gear combinations:

http://www.transmissioncenter.net/sp...n_______va.htm

The method used for "rolling" diameter is different than what I mention and it's a bit easier than doing all the math I mention but either will work.

 

I have the correct definition file for my year ($8D) but I don't
have constants/scalars that you have in $EE.

I only have VSS instrument panel pulse divisor (pic in 1-st post).

 

***The following is in ERROR!!!


I'm quite sure that '90 cars actually used a 2-pulse or 2000 VSS rather than the 4 pulse or 4000 VSS. The '90 shared the VSS from the late TPI of the '86 through '89 TPI cars. In '91 I believe they went to the 4 pulse 4000 VSS.

 

Sorry, the 90, VSS IS 4006.96 (pulses/miles), and pulse divider=0

 

I see that NOW after some research! I assumed (incorrectly I guess) that the '90 car shared the same VSS as the early TPI cars. The speedometer calibration I mention though I assume is still correct. Right?

 

The rest is good and, probably more accuarate of a method than what most would normaly do (I liked the link you posted).

 

The VSS information was passed on to me by a Delphi "tech" several years ago when they actually changed some part numbers on some VSS's and included a short harness to adapt it. It was a bad supercession and led to the '90 40-45 tooth VSS being NLA.I had never reason to doubt it!
I've done calibrations with DRAC's and DRAB's but I've never done anything directly with the PCM's

The information I researched today myself after your post is from this very interesting site: http://www.jagsthatrun.com/

 

That does interest me, I haven't had the opportunity to read it completly, but the little that I did read is on the money....The ecm info etc. is simply because I only have working with and tuning the 165 (maf) and 727/730 (sd) ecm's.

 

What is the function of instrument panel pulse divisor?

Can I correct the readings on LCD with it?

 

No. See post #5.

 

3% error is probably the best you are going to get.The different speedo gear sets available will not allow you to get any closer.

http://www.corvetteforum.net/c4/vett...Gearshtm.shtml

 

If you really want to dial it in, you could always use a signal interface.

http://www.dakotadigital.com/index.c...rod/prd126.htm

 

I would like to revisit this. Has anyone used this product before? I am trying to educate myself on this as I just picked up a set of C5 wagon wheels and would like to use the factory C5 tire sizes. The digital interface works with 8K and up pulses. What does the 1990's use? With the factory C5 rear tires I will have a ~4% error.

 

I use one myself on my 88 to correct for the 3.73 gears. I also use it to fine tune for tire size, since I'm running a 255/45R17 tire now.

Mine is an older model Dakota Digital SGI-5 that uses dip-switches for adjustment. I think its a revision "C" model. Its a universal interface that can handle just about any input frequency that you would ever need.

If the 90 setup is similar, you need to intercept the vss signal upstream of the instrument cluster.

 

just reading this post ,very intresting.what programmer should i buy for my 91 383 sr car to adjust speedo and other performance adjustments thanks