Will a gearing change effect the ECM?

[dla]

I'm swapping a 96 explorer 8.8 regeared to 4.30/1 under my 2007 2.3l,5spd,2wd Ranger. The explorer rearend has the tone ring speed sensor and the Ranger only has ABS rings on the front wheels. I'm just wondering if the higher rpm for a given wheel rotation will effect how the ECM manages fuel, etc.? My tire size isn't going to change, so my speedo should be good.

 

[dmac0923]

you need to keep the tire size to gear ratio the same in order to keep your speedo factory correct.

 

[Kona]

I think you have to have your ecm reprogrammed for the new tire size....I only have a mechanical speedo myself so I am just guessing the Ranger is the same as the bigger trucks.

 

[rwenzing]

My tire size isn't going to change, so my speedo should be good.

Your 07 Ranger's vehicle speed signal originates at the OSS sensor on the transmission and then gets corrected in the PCM before being sent on to the cluster. A change in rear axle ratio will affect the speedo calibration. Same story for a tire diameter change. The sensor on your rear axle is for ABS only.

 

[dla]

Your 07 Ranger's vehicle speed signal originates at the OSS sensor on the transmission and then gets corrected in the PCM before being sent on to the cluster. A change in rear axle ratio will affect the speedo calibration. Same story for a tire diameter change. The sensor on your rear axle is for ABS only.

Thanks for the info - I clearly didn't understand. Now this means that the speedo will be effected significantly. What, if anything, can be done to calibrate this to the new gearing & tires?

 

[rwenzing]

In the 2001~2006 PCMs, it was possible to recalibrate the speedometer correction factor using a dealer tool - within limits, of course. Rangers made the transition to Ford's new PowerPC processor in 2007 - I don't know if the procedure is exactly the same for those. A knowledgeable Ford dealer tech should be able to tell you.

There are also aftermarket calibration boxes that can be spliced into the wiring to change the speedometer calibration.