Tach testing

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JimG
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Tach testing

Post by JimG » Sun Aug 11, 2019 8:14 pm

How can i bench test a tach? I bought one at Carlisle but would like to know that it works before removing the cluster.
Jim Gosses
86 XR4TI, 165K, IC, RR, PBR Fronts, T-bird Rear Discs
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cmouta
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Re: Tach testing

Post by cmouta » Mon Aug 12, 2019 8:14 am

You need a a 12VDC power supply and a Function Generator that can produce square waves with a 10V+ amplitude. I thought I had it shown somewhere but the 3 posts on the back of the tach are 12V power, Signal, and Common. Your signal common and power supply common will both hook up to the same post.

Then use this chart to inject frequencies that correspond to RPM

The pulse frequencies are derived by a four cylinder engine firing twice per revolution so 2/60 * RPM = Frequency input.

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Chris
1988 Mono Rosso Red Merkur XR4Ti - Sold!

my8950
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Re: Tach testing

Post by my8950 » Wed Oct 02, 2019 3:22 pm

Function generator would be helpful for a lot of things, but hard to justify huge cost for just a square wave...

JimG
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Re: Tach testing

Post by JimG » Wed Oct 02, 2019 4:47 pm

Does anyone know of someone who could repair and calibrate the Tach?
Jim Gosses
86 XR4TI, 165K, IC, RR, PBR Fronts, T-bird Rear Discs
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Ed Lijewski
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Re: Tach testing

Post by Ed Lijewski » Wed Oct 02, 2019 7:18 pm

This device which creates a square wave is inexpensive to make. I used one to test a Scorpio speedo/odometer.

viewtopic.php?f=29&t=29946&p=273678&hil ... or#p273678

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