Tachometer problem
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Mountain Pass
Joined: Jul 2020
Posts: 156
Likes: 13
From: Wichita
Tachometer problem
Hey all, I recently bought a instrument cluster from a 1992 F250 7.3idi that had a tachometer. I swapped it into my 1993 ford f250 351w. I know that it see's it, when I start up the vehicle that tach moves a hair, and when I rev it, it moves a small amount, however it will not move past and or even close to 500 rpm. It just does little nudges from 0 - 200 rpm (probably). I have no idea what to do, any help would be very much appreciated.
Cargo Master
Joined: Nov 2009
Posts: 2,190
Likes: 620
I do not believe the tach out of a Diesel equipped truck will work in a Gasoline truck. Diesels do not have Ignition systems, so they derive their tachometer signal by other means (oftentimes pulling a signal off the alternator), and I'd bet good money they Diesel Cluster has absolutely no idea what to do with the ignition signal from the Spark ignition setup.
That you're seeing any activity, at all, is just due to the fact that it's expecting a 12VDC signal, but the signal you're feeding it isn't useful.
That you're seeing any activity, at all, is just due to the fact that it's expecting a 12VDC signal, but the signal you're feeding it isn't useful.
Logistics Pro
Joined: Nov 2013
Posts: 3,921
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From: Mojave, Ca
IDIs get their tach signal from a small hall effect sensor located on top the timing gear cover. I imagine there about 40 teeth on that gear so 40 pulses per revolution. The gas trucks get their ignition signal off the ignition module, I think, which is 4 pulses per revolution. Which explains your 10:1 ratio. I'm surprised it recognizes the signal at all. Unless you wanna program an Arduino board to boost the pulses 10 times, it would be a lot easier to get the instrument cluster for a gas model.
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Mountain Pass
Joined: Jul 2020
Posts: 156
Likes: 13
From: Wichita
Well then it looks like im the idiot, I just ordered a gas tachometer. The diesel Instrument cluster had a 4 pin connection available for the tachometer, however the diesel tachometer was only taking advantage of 3 of them. The gas tachometer had all 4. So I had already purchased it as of the first comment. *facepalm*. Well if it works great....will let you guys know.
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Mountain Pass
Joined: Jul 2020
Posts: 156
Likes: 13
From: Wichita
Update: Alrighty for all those wishing to know, a Gas Tachometer will work in a Diesel Instrument panel, on a Gas truck of the same year as a diesel.
This is my gift of idiocy to you all!
This is my gift of idiocy to you all!
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Logistics Pro
Joined: Nov 2013
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From: Mojave, Ca
You swapped the gas tachometer servo and needle and installed it into the Diesel instrument cluster?
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Cargo Master
Joined: Nov 2009
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Uh, you don't exactly have to disassemble the tachometer itself, if I remember the cluster in my '92 properly, the Tach comes out as a unit, the Speedo comes out as a unit, and I think like Temp/Batt and Fuel/Oil pressure come out as two little units. It's modular, it wouldn't surprise me, if you could take the tach module out of a Gas cluster, and plug it right into a Diesel Cluster. I don't know that for a fact, but I'd venture a guess, the actual construction of the "backplane" is identical.
Logistics Pro
Joined: Nov 2013
Posts: 3,921
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From: Mojave, Ca
Isnt the numbering all messed up too, since the diesel tach only goes to 4k? Sure, the needle moves, but its not accurate... or maybe it is. IDK, asking you for clarification. Maybe a picture.
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