My tach is not working (stuck at 0) and Overdrive OFF light is constantly on (switch on dash). I cleaned up the switch and wiring harness in dash but no help. I also check all my fuses and they are good. Anyone have any suggestions as to where to start troubleshooting? Also which OBD1 reader would you suggest for this truck? Thanks.
A dead tach sender should/would send the automatic trans into a "failure management mode" (limp mode) with harsh engagements and firm shift feel and an abnormal shift schedule. It has no effect on a manual trans only the Tach readings.
Check the wires where they exit the big nut on the oil filler housing , known to short out due to bare wire.....
Replace the tach sender on the oil fill housing a big 1" nut with 2 wires. Ford only part Engine RPM sensor E5TZ-17B384-A about $50. You can remove and clean it but usually changed later too.
You can test it too, hold it in the air away from ferrous metal, using an ohm meter lead on each wire you need DC resistance between 2000-3000 ohms.
93 F250 7.3 IDI S/C XLT 4X4 E40D 3.55LS, Captains chairs, Tutone Mocha, Leer 48" Hiboy cap, FR & RR hitches, full DeeZee running boards. Factory ordered/delivered Jan 93
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My 1990 F-350 7.3 has a intermittent tach working. It doesn't work until about a half hour of driving. When it isn't working, the transmission goes into limp mode. When the tach starts working everything is fine. I have replaced the tach sensor and still have the same problem.
Same component different problem.
My tach works most of the time, almost always at an idle it will drop to zero. Revving the the engine always re-activates it but sometimes I can also turn the headlights on or touch the brake pedal and it starts working. On one occasion it was erratic while running down the highway for a short distance kicking it in and out of over drive. I have tried different tach sensors. I am thinking corrosion somewhere. This problem started 5 years ago right before I parked it. It has been sitting for 5 years but as my '06 was stolen (see signature)I have to use this rig until I get back to work. Going back through all the connections again today but I can not find my wiring diagrams for pin assignments. Can anybody help with the pin assignments.
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