i have a 91 ford 7.3l and the tack works when you rev it up but doesn't work when it idles and it's making my transmission jump in and out of gear under a load but if i unplug it the transmission works fine i have herd it could be the tack sensor and some people has told me it could be the transmission cpu has anyone had this problem before?

 

tach sensor is ford only item, costs about 70 bucks or so. on the timing gear cover on left side of engine on top is a 2 wire sensor threaded into the housing. unthread it and clean it off, see if that helps. if not u need a new sensor.

 

thanks i clean it already so i will get me a new sensor from ford and see if it fixs the problem.

 

mine does the same thing. drops to 0 at an idle. going to try the cleaning