The tachometer sensor may fail on Ford F-350

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.

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Average mileage: 141,206 (100,230–167,000)
Drive Trains affected: 2WD, 7.3L V8 Diesel, Automatic Transmission, Diesel
5 model years affected: 1990, 1991, 1992, 1993, more1994
10 people reported this problem
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Viewing 1 - 4 of 4 problem details
1990 Ford F-350 - Automatic Transmission 137,596 mi,
Tachometer jumps around, even going to zero, causing irratic down and up shifting of the automatic transmission. Very disconcerting.
my tachometer quit and I have noticed a difference in when the transmission shifts. I replaced the the tach sensor but the problem still persist could I have an electrical problem with the fuse box , wiring, or something else. I am at a loss.
1990 Ford F-350 - 2WD 100,230 mi,
Have not fixed but doing just what u described
1993 Ford F-350 - 2WD 160,000 mi,
I have a 7.3L and the tachometer started dropping down and becoming erratic (after the engine heated up)then 1800-2000 rpm sometimes it becomes rock solid. So I bought a new sensor from Ford Dealer and I'm about to install it today. This circuit uses a HET (Hall Effect Transister) type pick up and is probably breaking down under heat. It does seem most people have the problem begin around 160,000.