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- Joined
- Jul 26, 2016
- Messages
- 4
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- 0
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- Vehicle Year
- 1994
- Make / Model
- Ford
- Transmission
- Manual
I found a tachometer cluster from a 1994 ranger 4.0 manual, and wanted to use it on my 1994 2.3l manual. The cluster worked with no modification, but the tach was about 200 rpm off. Turns out there is a potentiometer on the tach circuit board that you can use to adjust the needle. I discovered the error in the tach comes from a error on acceleration, and an error on deceleration. There was about 100 rpm error on the upswing (low reading), and 100 rpm error on the downswing (high reading). Using the pot I was able to split the difference and now have a better understanding of how it works. I also discovered the signal "Sig" must match input voltage. FYI you can pull the tach out once you have the cluster lens off, and the circuit board has four big pins on the back labeled: B+, GND, SIG, and CYL. Sig looks for a positive square wave signal. B+ and GND are battery positive and battery negative. I think CYL is used in Explorers with a v8. I do not know what Hz the ecu computer puts out vs actual engine rpm; example 100 Hz might map to 3048 rpm. Does anybody know?
