Contour Enthusiasts Group Archives Forums Modifications Transaxle Tech Question

I did lots of thinking on this when I posted it in the sticky at the top of this forum.

The EEC-V system is going to have a common core of programming used on all cars. The extra data that is specific to each car is added on to that common core. I mean it stands to reason that you would not want to program a different engine management computer for every car on the market.....

Now take into account that some cars are rear wheel drive and have the differential in the back. These cars measure the speed at the transmission output shaft, the part where the driveshaft is inserted into the transmission.
If the speedo is driven off of the shaft before the differential then it will be off if you change the final drive ratio. The example would be a mustang with (for example!!) 3.83 rear end and you switch to 4.11 rear end or something like that. The speedo will be off because it is mounted before the diff. In this case you would use the setting in the computer to change the calculation on the computer driven speedo.

With our cars the speedo gear is driven off the differential directly. The differential is always directly linked to the drive axles and wheels and so is technically mounted after the effective gearing. THerefore it is always measuring actual wheel RPM and NOT transmission output shaft rpm.

For further proof I looked at the wiring schematic. On our cars the speed wire goes to a splice, then it branches out into a "Y" with one wire going to the pcm and one wire going to the speedo. If you cut the wire going to the pcm then your speedo would technically still work because there is no wire coming back from the pcm to the speedo.
Our speedos are just electrical speedos driven off of the pulses from the speed sensor, nothing more.

I learned this when I came up with a way to defeat the electronic speed governor of the regular contours while still retaining a functional speedo. I never built the device, but I did come up with a tentative schematic and plan to implement it.

Tom