jumpy speedo

1994 chevy 350 engine 4speed trans my speedo needle keeps jumping and the truck starts bucking when in drive the odometer will keep adding miles even when im parked and the engine is running . whats wrong with the truck. i need help to fix this problem the trouble could is not in the pcm i did the ground and test thing but it just flashes 12 which is diagnostic mode
Reply to
tk_b
Loading thread data ...

check the wiring from the speedo pickup on the tranny to the rest of the harness. There migth be a short.

I will check in to it when I get back to my shop

Reply to
mathijs derks

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.