this is my first 12 valve cummins, it is a 92 and has the 518 auto o/d. when i got it the speedo would bounce and it would jump in and out of o/d around 45 mph. i found that the vss was loose and tightened it, no change. i pulled the speedo gear and it looks good, when i plugged in the vss again, the speedo worked, o/d worked, no odometer. i turned it off, and started it again and i had no speedo or o/d. unplugged and plugged vss in again and worked fine until i i shut it off, no speedo or o/d again. do you guys think the problem is the vss or could it be something else.

 

you could have a bad sensor. check the wires to see if they are broken. another thing that going bad is the ratio adapter that some of those. The computer also controls the speedo. Had to have my computer rebuilt for the samething. Is the AC and charging system working or is it only the speedo giving problems? I'd be looking to see if the ECM is bad if you have all those problems.

had.Spedo drive adapter

 

Here me out I was look up Ppumps stuff on YouTube and fond some vids for recall 605 not knowing if I should care, and being the owner of a 91 watched them all. In part3 minute 7 is the information helped my babe I had on speedo on odometer and she would hunt for OD I @ all speeds she would stay in if you were constantly accelerating… the long and sort is still on odometer speedos back OD is back and it takes 5 minutes a 10mm and good malta meter ... Or 5.9L Cummins Injection Pump Replacement Part 3