'91 F-150 302

Took the truck into AutoZone and had them pull the codes. It gets
poor mileage and runs rough, bucks at times... once in a while the
truck will completely stall while driving down the road.

They came up with three codes:

29 - vehicle speed sensor
31 - low voltage on EGR valve position sensor
32 - Same as 31?

In trying to research this in past posts and reading from material
from Wells (maker of the EVP), I just wondering if the vehicle speed
sensor can effect the EGR valve position sensor. I think I read that
the EVP takes in data from "how fast the vehicle is running..." (?)

Also, the speedometer and odometer do not work, but the tachometer
does.

Thanks for any help!

 

I think the gear may be gone on the end of your speedo cable where it plugs into the transmission. Without the gear your speedo cable wouldn't be turning, the speed sensor wouldn't be turning and your speedo would not work. The cable is very easy to pull out of the transmission, you can check the plastic gear on the end of the cable.

You can also test the EVP sensor, you can find how to do it on this board or go buy a manual for your truck. There are 3 parts to your EGR, the solenoid located by the ignition coil if your coil is above the drivers side valve cover, the EVP sensor on top of your egr valve and the valve itself. Check your vacuum lines for breaks, test the solenoid, test your egr and check the tube that runs from the bottom of the egr to the intake. Start with vacuum lines, if they are all good test the solenoid, if it is ok then test the EVP sensor and EGR. If those are all good then you may have another vacuum leak making those systems not function properly.