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possible to bypass VSS buffer box 1991 electric speedo?

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Old 07-13-2018, 08:41 PM   #1  
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possible to bypass VSS buffer box 1991 electric speedo?

long story short... my speedometer went out and i am trying to fix it. shot some wires and i have voltage going into the buffer box from the VSS. i also have good voltage from the "hot in run" pink wire going to the buffer box. i have zero voltage coming from the speedometer out wire from the buffer box.

is it possible to bypass the buffer box? i know the VSS is a 4k pulse output and the speedo looks for a 4k pulse input.

or is there anything else i can try and look for?
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Old 07-13-2018, 09:37 PM   #2  
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Re: possible to bypass VSS buffer box 1991 electric speedo?

Must of been a tbi car to have a buffer box. I don’t think you can measure the optical signal out of the buffer. Sounds like more of a ip issue. You could hook the cruise signal from the buffer cutting the ppm in half to test another output of the buffer.
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Old 07-13-2018, 09:55 PM   #3  
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Re: possible to bypass VSS buffer box 1991 electric speedo?

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Originally Posted by Tuned Performance View Post
Must of been a tbi car to have a buffer box. I donít think you can measure the optical signal out of the buffer. Sounds like more of a ip issue. You could hook the cruise signal from the buffer cutting the ppm in half to test another output of the buffer.
Yes it was a tbi car. I am guessing when u say ip u mean input? If so, the vss wires going into the buffer were measured at the plug and had correct ac voltage.

What do u mean by hooking the cruise? I did try and shoot all the wires coming out (speedo, cruise and ecm). None of the wires had any voltage output at all.
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Old 07-13-2018, 09:59 PM   #4  
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Re: possible to bypass VSS buffer box 1991 electric speedo?

Ip is instrument panel, the vss buffer has a cruise control 2kppm output you could feed that to the speedometer to see if it works. Since you have verified Vss input to the buffer power and ground to the buffer. Sounds like it’s a bad speedometer.
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Old 07-13-2018, 10:07 PM   #5  
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Re: possible to bypass VSS buffer box 1991 electric speedo?

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Originally Posted by Tuned Performance View Post
Ip is instrument panel, the vss buffer has a cruise control 2kppm output you could feed that to the speedometer to see if it works. Since you have verified Vss input to the buffer power and ground to the buffer. Sounds like itís a bad speedometer.
Oh ok I see what u are saying now. Thanks for the ideas.
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Old 07-13-2018, 10:11 PM   #6  
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Re: possible to bypass VSS buffer box 1991 electric speedo?

I don’t think the optical signal is something you could measure with a volt ohm meter. The buffer box is pretty reliable .
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Old 07-13-2018, 10:12 PM   #7  
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Re: possible to bypass VSS buffer box 1991 electric speedo?

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Originally Posted by Tuned Performance View Post
I donít think the optical signal is something you could measure with a volt ohm meter. The buffer box is pretty reliable .
Yeah looks pretty simple. Just a small circuit board. Nothing too crazy.
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