1990 f350 No overdrive and no tachometer - Diesel Forum - TheDieselStop.com
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Old 10-10-2007, 08:18 PM   #1 (permalink)
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1990 f350 No overdrive and no tachometer

Hi All,

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.
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Old 10-11-2007, 01:21 AM   #2 (permalink)
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Re: 1990 f350 No overdrive and no tachometer

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.
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Old 10-11-2007, 04:29 PM   #3 (permalink)
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Re: 1990 f350 No overdrive and no tachometer

we had the same problem on my dads truck

it can be a sensor in the transmission

or the tack sensor it self

the computer

a relay

or a problem with one of the wires
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