Speed/Od-ometer: Has anyone bothered to recalibrate?

[martinli]

Funny, I tried to download AS-Build-Data two days ago and got allways a server errror. But today - thanks for your input - it worked
But at a first look I do not really see whether this information will help.
There seem to be less AS-Build data fields for the GEM module as I can see in Forscan.


Still I hope there will be some more or less easy solution to adjust the speedometer.

[jblaze5779]

I think I changed my speedo gear from brown to orange and came up pretty accurate when running 32's. 2002 e350.

[Orv]

BTW, the reason most speedometers read high as-built is the US DOT regulations that manufacturers follow. They don't specify accuracy except that the speedometer cannot read below actual speed at any point.

Odometer accuracy is more tightly regulated. This can probably be traced back to Ralph Nader. While most people remember Unsafe At Any Speed for its criticism of the Corvair, he also pointed out that manufacturers were effectively shortening the warranty periods on cars by making the odometers all read high. (And this in an era when warranties were pretty short to start with.)

Not super relevant to the discussion, but I thought it was interesting.

[maxacceleration]

Easy,
I have a mph app on my phone which is stuck to my dash. I'm only about 3 mph off so I just make a mental note and if I forget just turn on my mph app. No need to throw money at it. 4.56 & 295/70-17.

[MadScience]

3mph at what speed though? It's not going to to be a constant number, but a percentage. If you're within 3mph at 70, then yes, you're fine.

The other reason to fix this is to make sure the transmission actually shifts at the right points, though 3mph at speed is again fine.

[maxacceleration]

Yes its 3-4 mph around 70 MadScience. Less of course at 30 mph +-.
In my case its over, so an indicated 65 mph is 61-62 gps.
Also my van (V-10) does not like to shift - I have to let off the accelerator.
But my 5 Star tuning (in the mail!) will adjust shift points anyhow.
I get one tune with 5 Star, Daily/Tow they call it. We'll see how that goes.
Just in time for a road trip!

[RLC85]

I’m having trouble getting the right settings on the Dakota digital calibration box. I’m doing a diy 4x4 conversion on a 99 E350 7.3. I added the new speed sensor from the 4x4 tail housing but can get the calibration right. I have a sterling rear with 4.10’s and 35” tires. Can someone let me know what settings they used on the sgi-5e. The closest I got was on L-L with a .250 calibration on terminal 1, but it’s still 5ish mph fast and the terminal 3 won’t display a speed. Thanks

[MadScience]

You can only use certain outputs with certain vehicles. Not getting anything to work on some of then is normal/expected. This took me a second reading of the manual to understand.

Here's my spreadsheet dump from working this out on my '99 v10 with a more recently rebuit 4r100. Hopefully it helps with your math.

However, a couple of notes first: When I got my van it was using the output on the transfer case, which is lower tooth count and ~ 2000 pulses per mile. Since I want the van to shift before redline in low range way more than I care about an accurate speed reading in low range, I switched back to using the transmission output which is ~ 8000 pulses per mile.

Side bar: I really wish I could find or figure out where this adjustment was previously made on my van. I have not found anything to adjust in IDS, nor did tracing any wires locate another calibration box anywhere. Nor do the vans use the older digital odometer PSOM. At this point I'm not entirely dismissing the possibility that there was a 2wd 4r100 in 99 that used 2000 pulses.

So I'm just doing the huge downconversion in the Dakota box. It works fine at speeds over 10 mph, which is all that really matters anyway. Pulling away from a stop, the speedo has a bit of lag.

To do the calculation I measured the speed that was being indicated at IIRC 25 mph using a GPS and then calculated the pulses I was seeing. From there I tried to guess some factors by hand, but kept missing. Then I made the following spreadsheet, got a factor and it's dead on, at any speed:

tires revs / mile 630
axle ratio 3.73
4r100 tooth count 18

actual pulses / mile 42298.2
expected pulses / mile 8000

factor (actual / expected) 5.287275

1/16 of pulses 2643.6375

factor to correct 1/16th 3.0261335

set to h-l using output 3 which is 1/16th and the above factor

[RLC85]

Thanks for the info, seems like I’ve tried every setpoint and calibration on both output 1 and 3 and the only one I could get to work was L-L and .250 on output 1. The low speed reading might be my problem, I’m not able to get above 20 in my area and not ready to take it on the highway. I’m pretty sure my speedo is a 8000ppm and the sensor is putting out around 42000 ppm. My next step is to jack up the rear end and see if it shows a speed with the H-L setting.

[Flux]

after I put in my info and tuned with the 5 Star tuning my speedo is quite accurate. Checked it with GPS. It was on the money.