Hey there diesel mechanics i got a problem! And i have tried all day to figure it out.. i have a 1991.5 cummins,i parked my truck and all functions were perfect.. start it the next day no wait to start light hmm odd, start it up take off no speedometer hm okay.. also no 4th gear but goes through 1 2 and 3 perfectly fine no slips no clanks so i did some reading.. change the vss okay i did that.. nothing.. change the vss connector hmm did that too put a jack on the end rais it up unplug the vss and reducer use a mirror to make sure gear is spinning inside the actual tranny its self.. it was. Hmm take out the reducer and only use the vss? Not working.. check for a voltage reading on the vss wires. I believe it was 2.7 hm okay take the speedometer out and checked the little blue gear inside of it, it was okay in tact with teeth..hmm fuseable links? Lets test them.. all recieveing power to my knowledge using a test meter. Hmm im out of options guys? What can i try next? Btw i ordered and 3rd vss just to triple check.. is it possible the reducer connected to the vss is bad? But i inspected and cleaned it and made sure the little metal sqaure peice sticking was still square and rotating easily as it was doing just that.. checked fuse panel all fuses reciving power.. I believe the tps is working i cleaned it also.. also cleaned the battery and unpluged it for 10 mins, also cleaned alot of the grounds.. im at a complete loss to why my speedo wont work and why i cant go into 4th gear i have a 46rh tranny 4 gears and over drive i also fucked with the 4x4 trying to get the tranny to do anything but it didint fix my problem. Any ideas guys ?

 

Is it my pcm? Since my wait to start also stoped working and my speedo and my over drive? Vss okay along with wiring and fusable links