Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Went for my first test drive yesterday and my hdx speedo was reading extremely low (didn't read over 20-25 mph, even at a cell phone gps indicated 55-60). I tried to do the adjust procedure in the gauges but was only allowed a max of 125% which was nowhere close to where I need to be.

I am figuring I need to make a change in the pcm through HP Tuners. I've got a t56 with a 4.56 rear (which is likely the cause of the speedo reading so low). My concern is I've read online that making too large a change in the pcm will brick it. Is this still an issue? What can I do to avoid messing it up? Anybody know? I'll have an opportunity to get into the pcm when it goes on the chassis dyno and make any changes but I need to get it right the first time since I personally don't have my own copy of the software.

Thanks!

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

All of the VDX/HDX units I have seen calibrate the speedo by putting the system into calibration mode, press button, drive 1 measured mile, press the button again.

how dies yours calibrate, and how do you have it hooked up?

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Mine is getting all data through a bim module from the pcm. In this configuration all you can do for speedo calibration is adjust the incoming vss signal up or down 25%.

I know I can adjust the signal out of the pcm to the cluster through HP Tuners but am nervous because apparently its possible to piss off the pcm and brick it with too big of a change in these tables. Even HP Tuners acknowledged this in their forum but the posts were quite dated so I don't know if its still an issue.

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

I've never had a problem changing gear or tire size within the PCM. Not saying it can't happen, but never seen it.

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

If you are getting the info through the BIM module then you need to calibrate the speedo through HP tuners.

If you are tuning yourself just go to go to Edit - Gear/Tire wizard - enter your tire size and gear ratio and hit the adjust button. 4.56 is well within acceptable parameters unless you are running some tiny wheel/tire combo.

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Just a random helpful tidbit - I used to try to calibrate by driving by one of those radar speed signs, but besides being inconvenient it's not super accurate because they're at an angle.

If you've got an iPhone, there are a million GPS speedometer apps, and I imagine that feature is built into Maps as well. So you can check your speed pretty accurately that way wherever you've got a decent view of the sky.

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Ok, thanks Rob.

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Cool, thats what I will look for when we get set up.

I believe my rear tire is 28" tall so should be no issues there.

Thanks!

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Yeah, I have a GPS driven speedo app on my phone. It was my only speedometer when I put the T56 in and my dash speedo no longer worked. It was also how I saw the current DD speedo is so far off.

Thanks Dave.

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Off subject but how do you like the 456s with the T56. I’m running a 5.7 with T56 and 350 gears in. Ford 9”. Was thinking about going lower but like 373
Thanks. Hope you solve your problem
Steve

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Hey Steve, the 4.56's are no problem with the six speed. I still use first gear and (at least with the previous engine) still don't see sixth gear until 80 mph. I bet you could even get away with 4.88's with this setup but you *might* turn first into a granny gear. Sixth has pretty much been a glamour gear for me. I am rarely on the interstate so have only gotten in it once or twice (and that was just to see how it felt). Looks great on the build sheet though :lol:

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Follow-up - got the wheel diameter and gear ratio corrected in HP Tuners yesterday and speedo is now only off one or two mph off GPS. I can correct that through the gauge cluster.

Now to figure out why the cruise control doesn't work....

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

What year engine, and how do you have it hooked up, LED tail lights?

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

Well, that confirms the 6 speed for me........80+ !

3:73 and a TKO 600 and maybe 3% highway was the right decision 13 years ago

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

I can use it a little sooner with all the torque of this new stroker. I think I got into it around 65 but it was borderline lugging the engine.

Re: Speedo calibration - Dakota Digital HDX/ HP Tuners
 

04, DBW, speartech standalone harness with cruise control added in (four or five wires from the harness IIRC). Dakota Digital cruise control stalk with all the relays inbetween the stalk and the harness to get the signals right. No LED lighting...

I just need to get under the dash and go over my wiring, maybe do some metering to see whats going on (or not going on). Got some other stuff thats higher priority. Heck, with the exhaust on it, I'm not super interested in any long rides down the interstate yet anyway. Its LOUD!!!!