factory tachometer dead!

[smitty97]

hi all, im new to this forum, and diesels as well. just picked up a '88 f250 4x4 cheap, and it needs some tlc. i had lots of fun repairing the fuel lines that were leaking and eating my driveway.

anyway, among other issues, the tach is DOA. normally id trace back from the distributor to fix this, but this is a different animal. where should i start?

thanks
-tom

 

[dsblack]

Welcome!
The tach pickup is the big nut on the drivers side of the oil fill with two wires comming out of it. Check there. These do fail, and are a ford item. Less than $100.
Please be so kind as to add some to your signature under profile. So we can know more about you and your truck. Such as if you have a E4OD the tach will feed to shifting the trans.
Good luck! Let us know how it goes.
Doug

 

[smitty97]

ok, thanks, ill check it out. i think its a C6, its a 1988 and there is no OD on the PRND21. i definately wasnt getting OD on the highway this morning. is the pan a different shape?

 

[dsblack]

Ya, sounds like you have a C6. So it will not have any impact to the truck, except drive you nuts!

 

[Mr_Roboto]

E4OD was not produced until 1989. The only diesel auto in 88 was the C6 (AOD was used with light duty gassers only).

The tach sensor usually fails because the wires will break right where they come out of the sensor. It would be worth taking a few minutes to take the sensor out and inspect the wires and see if they can be repaired / soldered. I wouldn't recomend this on an E4OD but on a stick all that will quit working is the tach if the repair fails.

New tach sensors (Ford name RPM sensor) run about $60 - $65, it's a dealer only part.

 

[smitty97]

well i finally got to taking out the sensor.. checked it with an ohmmeter, it checks out ok. 2500 ohms sensing nothing, goes to 0 waving it very close to steel. i guess im looking at wiring now, or should i just assume the factory gauge is kaput?

 

[Agnem]

I'd swap the sensor anyway. Too much imperical evidence that they go bad. If it isn't bad, then you've got a spare, or one to sell somebody. If it isn't the sensor, you'd have to pull the instrument cluster and do your ohm check there. That would confirm if the gauge is kaput.