I replaced the VSS in my 91 d250 and the speedo is still jumping around. Does anyone have any suggestions.

 

you check to see if the computer is reading a steady speed or if it is jumping around also. (with a scan tool) if it's steady you could have a bad speedo.

 

Excusing my ignorance, but where do you plug in a scan tool? To the ECM?

 

in the plug under the hood on the left side should be just under the hood hinge. If you can get your hands on a DRB they are the best to use but snap-on works fine too.

 

I had no idea we could scan these things. Learn something new every day. Thanks Jwirth!

 

not as good as obd2 or 3. Had to scan mine tps and vss have gone out on me. and I'm not one to rig up delete kits. So I have fixed and repaired the wiring harness and had emc rebuilt. Truck was a wiring nightmare thanks to some Jaska$$ that had no business working on vehicles. it was so bad they straight wired the ac to the ignition because the (relay was bad) so the ac wouldn't cut off. my 7 way in the back had 2 wires that rubbed against the frame. So when I got under there to check it they used yellow wire on all 7 wires. I ripped that **** out and put it back with the right color wires. It doesn't take that long to do something right the first time. People say these trucks have wiring problems. only problems I've found is man made after someone worked on it or also being the trucks are 20 years old. no to many vehicle 20 years old or older don't have wiring problems do to age

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connector is L shaped btw