So I made the change from 3.31's to 3.73's last week and I also bought an SCT SF3 tuner from American Muscle. I had the tunes setup for the new gear ratio (3.73) and did not load the tunes until after the 3.73's were installed. When I start the car the speedometer bounces down below 0 MPH and then settles back on 0 MPH instead of bouncing up like it normally would and then settling down to 0 MPH. Also, the speedometer is reading about 5-7 MPH faster than I'm actually going when I'm driving. I called Bama/American Muscle and had them re-write the tunes for me and it's still doing the same thing. Any idea what could be wrong? I guess I will try calling Bama again on Monday, but it seems odd that the speedometer is doing the same exact thing.

 

Could be the stepper motors. I had to have mine replaced because my speedometer and tach would stop working randomly. Found a service on eBay that did it for around $80. Had to be without gauges for a few days but it was the cheapest way to do it. I know the stepper moots were a problem in the early S197s. 05-07 I think and then they upgraded them. Worth looking into..

 

theres quite a few repair videos on youtube also.


you might try reflashing to the original tune just to see if it might be tune related or coincidental- if running mods though(other than gears) wont want to drive on the wrong tune...but just to verify

 

I did try flashing the car back to stock. The speedometer is still off, which I would expect since the car has 3.73's now. No idea why it's off when the tunes are setup for the new gears though.

 

It sounds like the speedometer is not calibrated correctly! We can definitely look into this for you and make sure we're adjusting for the 3.73's properly. There's a few things this could be but the most common is going to be us adjusting the tune correctly.

If it's not related to the tune, laxplayer has a good point. It could be the stepper motors. The early 05-07 Mustangs did have a slight problem with these! If the car continues to do this after we make sure the tune is written properly, you may want to look into the stepper motor.

Shoot me a PM with your order number and I'll have a Bama tech contact you directly!

-Dan

 

Thanks Dan. PM sent.

 

Doesn't the buyer just set the tire and gear ratio under user adjustable options like I did with my x-cal2?

 

I haven't messed with any of the adjustable settings. I have no idea how they could not have programmed that in both times that they created the tunes considering you fill out a form of about 20 questions letting them know the specs of your car.

 

Ah, understood.