Speedo Correction

[hquick]

After the installation of the 0411 I've had to make a few changes.
I noticed I seemed to be passing most people on the freeway at the given speed.:)
In checking my speedo calibrations I found that the wrong diff ratio (was 3.43 mine are 3.73 according to the code in my glovebox which lists GT4) was in there as well as tyre size.
I used the tyre size calc to reset it (245 75 16) and it came out at 30.47".
Upon using this, I found my speedo was still out. I measured the tyre height from the ground to the top of the tyre...using a level to make sure it was an accurate measurement and I get a height of 28.75" (my tyres are getting worn).
I inserted this new measurement but when monitoring my drive to work this morning, the speedo was saying 100kph but the scanner was saying 96!
I just adjusted this in the speedo cal table. Will this be right now?
There is a speed camera on the way to and from work...I don't want to find out the hard way I've done it wrong.:bash:

[Biggsy]

Get your hands on a GPS, I use one to confirm my calibrations. They are very accurate. (unless Uncle Sam starts turning off Sattelites, which has happened in the past with wars)

[hquick]

But it's not really an option right at the moment.
I loaded the re-cal'd speedo cal but it's still out by around the same 4k's.
Any idea's?

[eboggs_jkvl]

How are you doing the "update"? What steps are you taking. Are you sure you're doing the update, the save and the load properly? This part of the program is usually pretty straight forward.

Verify tire size (or enter)
Verify Tire recalibration is done
Verify correct Final Drive ratio
Click "Apply"
Save File
Load file.

Is that what you are doing?

Elmer

[hquick]

Hi Elmer,
yes, that's exactly what I did.
Then I went through the fine tune process of adjusting the speedo to the speed shown on the EFILive dashboard/scanner.

[wait4me]

If you see being off by just a few. Then go to the "Speedo Fine Tuning" and put in your actual, and the dash numbers, then it will Fine tune it for you.

[hquick]

Thanks Jesse,
I tried that already. I'll try again. Maybe I did something wrong.
Actual is the speed being read by the scanner right? Not the trucks dash.

[wait4me]

No you need to go by the DASH. Scanner could be wrong due to the Cluster itself could have been programmed with a different speedo value.

[hquick]

OK, thanks.
I'll give it another go this arvo.

[hquick]

So, are you saying I really need to use some other devid\ce for reading my speed?
I insert my speedo speed in the 'displayed speed' box and insert a speed as read from a GPS in the 'actual speed' box

OR

I insert my dash speed in the 'actual speed' box and insert the scanner speed in the 'displayed speed' box.

[Blacky]

To get an accurate calibration, "real speed" or "actual speed" MUST be measured independantly of the vehicle speed sensor on the vehicle.
i.e. you MUST use a radar gun, or GPS or some other external speed measuring device.

There are two factors that come into play here:

1. The VSS pickup may be calibrated incorrectly in the PCM and the dealer or whoever last worked on the car may have "corrected" the problem in the cluster - instead of in the PCM. So if you correc tyour PCM, the cluster will be read wrong.
or
2. The VSS is correct and the cluster is incorrect.

You can't really tell which without an independent measurement.

The best you can do without an independent measurement is to measure the distance travelled by one complete tire revolution (or 10 or 100 would be more accurate if you have the space, then divide by 10 or 100) to determine the rolling circumference of the tire.

Then plug the values into EFILive's speedo calculator and let it figure out the correct pulses per mile.
You should be reasonably confident that the scanner will now be reading the correct mph - regardless of what the cluster is showing.

Then you should be able to adjust the speed displayed by the cluster without changing the actual pulses per mile by changing the speedo output pulses calibrations - hopefully your vehicle has that cal. i.e. H0105 in the LS1 cals.

Regards
Paul

[kbracing96]

Ok, so I jump in the middle and do a little thread whoring, lol. My scantool speed reads dead on my GPS, but at 80MPH, the cluster speedo reads 82. Is there a way to change just the cluster reading to match the Scan tool?

Edit: after reading a little more I believe I have come to the conclusion that I should be able to take 80/82=.9756 Then * that by 4000 (H0105) and come up with about 3900. That should fix my speed difference without affecting the scantool speed, right? Also, if H0105 is the primary output rate, then what is H0106, the secondary output used for? (just wondering)

[wait4me]

Tech 2 would be needed. That or just change the speedometer pulse output to fine tune the speedo cluster only. That is H0105. But, it is always better to just change the H0101, And just let the pcm be 2 mph off at 80. That is not very far off in terms of gm slop. .

[hquick]

Hey KB...whore away.:D
I ran a couple of 1.5 hr logs today during a long trip. Freeway as well as winding hills.
On the way home there was a speed check area...where the display is mounted above the overpass. I don't know how acurate they are but I was the only car on the road and at the point where you check the speed, I was spot on 100kph via my speedo. The display on the speed check sign said 95-6 as did the scanner.
I think I'll leave it. I'm happy for the cluster to be reading 4 k's over. I'm less likely to get speeding tickets that way! Now, if I can just make myself forget it reads 4k's fast!:D

[gto_in_nc]

Do the speedo and odo use the same pulses? If so, a fairly precise determination of the variance can be determined without radar or GPS if a measured mile is handy.

[Blacky]

Yes, as far as I know they do use the same pulses. Maybe some vehicles exist that use the ABS sensor(s) for odo - but I doubt it.

The trip computer "distance travelled" would be an option as well, since it usually has 2 decimal places of accuracy.

Regards
Paul

[Biggsy]

I know holden do tend to make their speedo's show 1-2% higher reading than actual, even on their earlier electronic speedo's (unless you have an ex-cop, their speedo's got calibrated regulary)
I have seen brand new cars showing 5% higher than actual!

There is a PPK (pulses per km) setting which they adjust the speedo with through the tech 2

Cheers,

[gto_in_nc]

thanks, guys! that's perfect and just what I hoped/expected. (The intentional miscalibration being a litigation avoidance measure, I suspect.)

I think I would be very hard-pressed to measure a tire circumference to within +/- 0.5% and, while +/- 27 feet over a mile is not GPS-spec, it is pretty darn good. Plus, I have a measured three-mile nearby, which makes it like +/- 0.17%. I can live with that... :D

[hquick]

I just noticed, when I put my tyre dimensions in the calculator it comes up with 245x75x16 = 30.47in. If I do the same in JET's DST it comes up with 29.58in.
Any thoughts?
The JET calc was much closer to my measured diameter.

[Blacky]

The calculation EFILive uses is:

d = ((w/25.4)*(p/100)*2)+r

Where:
d = diameter in inches
w = width in millimeters
p = profile in %
r = rim diameter in inches.

So for 245x75x16, you will get:

d = ((245/25.4)*(75/100)*2)+16
d = (9.64567*0.75) +16
d = 14.4658 + 16
d = 30.47 inches

I'm not sure what calculation Jet uses, or whether Jet adds a "fudge factor" to attempt to account for tire distortion, tread wear or any other factor that may cause a difference.

Regards
Paul

[Ira]

Ok, so I jump in the middle and do a little thread whoring, lol. My scantool speed reads dead on my GPS, but at 80MPH, the cluster speedo reads 82. I

Having spent way too much time with 97-02 F-Body clusters on the bench connected to a signal generator I can promise that in general their speedos are not very linear. Some are perfect over the range 20 to 80, but others vary by plus or minus 2 or 3 MPH over that range. If you check it at every 10MPH and it's always high, just drop it by 1.5% or so. FWIW, it will change over 2% over the life of a tire so reading 2MPH high might mean it's time for tires!

Ira

[hquick]

I think I've got it as close as I'm going to get.
3kph at 100kph is OK. You're probably right on the tyre wear issue.
The thing I really don't understand is how the diameter size calculator is different from the 'competition'. Also, the EFILive calculator was out by around 2.5"