mcgyver5150

Does anyone out there know if it can be done or how to do it?

I lowered the truck and then went slightly taller on the tires to really fill the fender openings. Truck looks great now but my speedo is off.

I knew it would happen, but I figured I could live with it. I've changed my mind and want it to read accurately.

Can this be done by changing a gear in the transmission or does it have to be done through the ECM?

Just some background on the truck....Supercharged 5.4 with JDM underdrive pulleys and idlers; elec fans, 3.73 gears........nevermind ...list is too long!

Lemme know if you can help!

KStromberg

OK, now your truck has the OBD2 computer which controls things in a much different way than EEC-IV. The VSS is used by the PCM to sense the vehicle speed but the speedometer actually uses the ABS sensor(s) to sense the vehicle speed. So, you do not need to change the VSS gear for the speedometer to be correct. Pretty neat, huh? BUT wait, the PCM is still reading the VSS to get the vehicle speed! Now what? Well, one of the beautiful thing about the OBD2 vs. the EEC-IV is the OBD2 can be programmed to read the VSS differently. It does this by being "reprogrammed" with a flash, a plug-in tuner or a chip. You could not do this with the EEC-IV! So now, you can leave the VSS gear stock since the PCM can be reprogrammed to interpret the VSS signal appropriately and the speedo works off the ABS sensors.


With those mods, it sounds as if you are way overdue for a good tune anyways if you haven't already.

Good Luck!

__________________
-1992 Ford F-150 (winter truck)
-1998 Lincoln Mark VIII LSC (fun car)13.591@101.72mph

cowboy24

try the hypertech max energy programmer, it accesses your speedo program, and asks you what your tire diameter is,(in 1/4" increments) you can also add injector timing and pulse width,trans shift firmness and read and clear codes,you'll like it!!