The tachometer sensor may fail; if the tachometer needle jumps around and the transmission has harsh shifts or does not upshift, this sensor should be checked. This sensor is mounted in a cover at the front of the motor.
Average mileage: 154,375 (108,500–200,000)
Drive Trains affected: 2WD, 4WD, 7.3L V8 Diesel, Diesel
20 people reported this problem
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When at idle tach drops to zero then when accelerator is pressed it jumps to appropiate engine speed
transmission won't shift out of low. speedo needle jumping, or not moving
Tach stopped working - Transmission won't shift out of 1st gear
This I think is also causing the engine to hover when at a constant speed.
I have the same issue right now. Before the tach wasnt working at all. Then I screwed around a bit with the sensor and it started to work, but a month of two later, it started to jump around allot causing it to shift quickly between 2nd and 3rd gear very quickly over and over again for 10 minutes on the road. I just replaced the sensor with a brand new OEM one, and so far its stopped. So all hopes that it just needed a sensor.
just started had to order part
needle jumps below 1400 rpm and shifts incorrectly above this its ok. im going to try the sensor.