Speeedometer Adjustment

[curtbriggs]

I changed to 315/30X18 tires on the rear, OD went from 26.1 to 25.5". In Navigator, Speedometer, parameters. The VSS config. window that opened had tire diameter and a "New" window, which I changed. The Diff. window had 1.000000 and a window for "New" I put in my ratio, 3.42. Is this correct? What about the "Adjust" "Save" and "Revert" buttons?? I clicked on save.

[Blacky]

On a vehicle with the speed sensor (VSS) pickup on the transmission output shaft the PCM measures the transmission output speed directly and by multiplying by the diff ratio the PCM can calculate the axle speed.

On a vehicle with the speed sensor pickup on the rear axle (like the Corvette) the PCM measures the rear axle speed directly and by dividing by the diff ratio the PCM can calculate the transmission output speed.

However, in the corvette the PCM does not use the diff ratio to calculate the transmission output speed from the VSS. Instead the "tuner" (that's you) must calculate the number of times the transmission output shaft will rotate per mile, and enter that value in the "Ratio" calibration.

EFILive should do that automatically - but the speedo calculator still needs some more work to cater for ALL possible configurations.

So for now, on a Corvette, you need to follow these instructions:

Make sure the Transaxle checkbox is checked. EFILive uses the VIN to determine if the calibration is from a Corvette or not. If the VIN in the calibration does not accurately describe the vehicle then EFILive may set the transaxle checkbox incorrectly.

The VSS pickup on the rear axle has 40 teeth and produces 40 pulses per axle revolution. That means if you have a 3.42 diff then the PCM will see 40/3.42 pulses per transmisison output shaft rotation.
That is the value that should be in "Pulses per rev". In your case it will be 11.6959. You should type in that value in the table of figures against the caption: "Vehicle Speed Sensor Pulses per Revolution".
Then click the [Revert] button which copies the data from the table, up to the speedo calculator. You should see the diff ratio set at 3.42.

Now that the PCM knows the final drive ratio, you can adjust your tire diameter. Enter the new tire diameter and click the recalc button.

The pulses per mile and Ratio values should change to suit the new tire size, and the Adjust box will have a -ve % value in it. That value indicates the change that needs to be applied to shift tables to make the PCM shift gears at the same engine RPM as before any changes were made to the diff or tires.
When you click the [Adjust] button you will see a list of calibrations that EFILive recommends be modified. Select them all and click on the [%] button to automatically update all the selected shift tables by the specified percentage.

Click the [Save] button to copy the newly calculated values back to the table data.

Regards
Paul

[curtbriggs]

Wow!!!
Thanks, Paul.

Curt

[curtbriggs]

Paul, every thing worked exactly as you said, except the adjust button gave me a "not available", is that because I have a manual transmision? The adjustment window is 0.00000%.

Thanks, Curt

[Blacky]

Paul, every thing worked exactly as you said, except the adjust button gave me a "not available", is that because I have a manual transmision? The adjustment window is 0.00000%.

Thanks, Curt

The "Not available" message in any of the windows means that the value cannot be computed because a divide by zero error would occur or because one of the values on which that value depends is set to "Not available".

Off the top of my head, I do not know why the adjust value would be set to "Not available" I am investigating...

It is calculated from the old and new pulses per mile values as follows:
Adjust = 100*(old-new)/old.
Is the old value set to 0? Actually in testing this just now, I discovered that you will get a "Floating point exception" if you attempt to set the ppm to 0 in the table and then click the [Revert] button.

Note:
The old value is the first value in the table named "Vehicle Speed Sensor Pulses per Mile".
The new value is the value displayed in the speedo calculator as "Pulses/mile:".

Regards
Paul

[curtbriggs]

Paul,

Pulses/mile: 31636 and pulses/rev is 11.695906 as you stated.

Tatio: is 2704.878100 and Diff: is correct at 3.42

When I hit adjust I get "This feature not available yet".

Curt

[Blacky]

Paul,

Pulses/mile: 31636 and pulses/rev is 11.695906 as you stated.

Tatio: is 2704.878100 and Diff: is correct at 3.42

When I hit adjust I get "This feature not available yet".

Curt

The Adjust option was only activated in the latest release V7.1.8. You can download that version here:
http://www.efilive.com/downloads/downloads_7.html

Regards
Paul

[curtbriggs]

Strange, I deleted 7.1.7 and down loaded 7.1.8. the day after it came out. Date Feb. 10, 2005. My Scan Tool says 7.1.8 .

Curt

[Blacky]

Strange, I deleted 7.1.7 and down loaded 7.1.8. the day after it came out. Date Feb. 10, 2005. My Scan Tool says 7.1.8 .

Curt

What version does the tuning tool have in the Help->About window?
Paul

[curtbriggs]

EFILive-Tune.exe V7.1.8 (Build 175)

Curt