I'm having a hard time imagining that a cable problem could cause the tach to read extremely HIGH. Low or no reading at all I could understand.
(I had a few seconds pucker factor when my tach dropped to zero when the cable failed very low over the trees during takeoff from Antique Airfield in Iowa. Then I saw that the engine was happy and I returned to home base for repair.) For it to read high, I'd bet that the problem is inside the tach itself. If your mechanic has a spare tach cable, it might be worth spending some time installing the replacement cable to see if that solves the problems. Those cables do fail and I know I had to replace one when my Coupe was new (to me). But I wouldn't spend a hundred dollars of shop time testing this, personally. Ed
