Speedometer correction with speed sensor in the differential?

[turboexplorer]

One of the last things that I can't figure out or find any information on is how to correct my speedometer when the SAS is completed. I have a 98' so the speed sensor is in the rear diff. I have talked to James here on the forum about him doing it through a tune or through SCT programers etc. He says that he can't do it, Ford doesn't let him into that section of the PCM. Has anyone found a way to correct it? I have 37's so the speedometer will be WAY off. I also think Ford can only reprogram it to 31's since that's the biggest tire you can fit on it in stock form. I can't find anything on the subject. Any help would be greatly appreciated! Thanks.

 

[DB_1]

http://www.superlift.com/accessories/truspeed.asp

 

[turboexplorer]

Looks great! Expensive but great. Humm...Dads an electrical engineer maybe we could make one?

The rear diff speed sensor is a VRS sensor so it makes its own voltage as the tone ring spins past it. But, does the computer read it as the amplitude of voltage as it spins faster it creates more voltage, or does it read frequency?

 

[carboncanyon]

I had a superlift truspeed on my superduty. worked fine. Sold it when I found a program that could reprogram my computer for 35s (Autoenginuity). The truspeed tapped into my ABS module and only changed the speedo. The overhead computer for fuel mileage used something else tho, as it didnt change until I did the computer reprogram.

Look at Autoenginuity, or find someone that has one and see if it will do speedo recal's on a 98. It did on my 2000 ford. I nutted up and bought it since I needed it to troubleshoot all the different fords I own, so it was worth it to me. Cheaper to buy the truspeed if your only messing with one vehicle tho.

 

[turboexplorer]

Okay I'll look into it. Thanks!

 

[Turdle]

The dealership has a box which sets the speed sensor according to tire revs per mile. You can find this from the manufacturer of your tires.

It's the same box they use to cycle the ABS pump. I believe it is called a breakout box.

 

[turboexplorer]

Okay ill also talk to them. My local dealer in WY is less than helpful. Will see what they say may have to wait until I move to Salt Lake

 

[carboncanyon]

The breakout box goes between the engine and the computer to do pinpoint tests of all the wires going into the brain.

The box that does the tire recal (and everything else Ford claims only they can do) is call an NGS or Rotunda New Generation Star tester.

In the early days, it was the only box that would talk to a ford computer, but nowadays you can buy pretty much anything online and get the same results. I believe Sniper Tuning has a box that can recal your speedo and do your own custom tunes.

The Autoenginuity is more of a troubleshooting tool with very basic reprogramming options such as speedo recal and I think some basic security reprogramming. I havnt used it on anything newer than a 2004 superduty.

 

[j_mazala]

I run a Dakota Digital SGI-5 in my 98 and it works great.

Install was fairly easy. Ignition hot 12v and ground to the unit, then cut the gry/blk(I would double check this first, you want the signal output wire from the pump) wire at the abs pump wire loom and wire the pump side to the input and loom side to the output on the unit.

About $75 from Summit

 

[turboexplorer]

So you have it set up to interrupt the signal after the ABS module?

So it is then sent to the PCM as the correct signal for trans shifts, speedometer, odometer etc?

 

[carboncanyon]

Sounds like it works the same as the truspeed, as that is how my truspeed installed.

I noticed a difference going from the tru speed, to an actual computer recalibration, so I think the ABS module only runs the speedo, but not the computer and trans. But again, this was on a superduty.

 

[turboexplorer]

The abs module is getting removed during the solid axke conversion. But I will keep the eletronic part so speedo will still work. I would be surprised if it really affected my trans. When its in 4Lo (didn't have from factory, 4406 installed) it shifted through all gears fine even though it was in 3rd and converter locked at 15-20mph It always acted fine from crawling to 30-40mph through the sand dunes. And speedo was always correct since its off the diff but trans shifted at normal rpms even though wheel speed was way down.