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SN95 Cobras
Tach reading double?
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<blockquote data-quote="mwolson" data-source="post: 11777694" data-attributes="member: 16006"><p>If you can, run the test I described in my write-up. If, for some reason, something broke in the tach, it will read 3600 RPM rather than the 1800 it should. </p><p></p><p>On the PCM side, I can't figure out how the PCM would put out a 2X tach signal, unless there is noise in it.</p><p></p><p>There is some adjustabillity in the tachometer calibration adjustment pot on the PCB of the tachometer circuit, but it is not enough to double it. However, there is a ground trace on the flex circuit on the back of V8 clusters that is cut on the V6 clusters. If that ground trace is not making contact for some reason, it would turn your tach into a V6 tach. If you add the adjustability of the pot to that, you might be able to get to a 2x difference. (Your tach is acting like a 4 cylinder tach for some reason.)</p><p></p><p>I assume you are running the Cobra PCM, not the Mk8.</p><p></p><p>If you run the test in my writeup, run the test for both the V8 and V6 tachs to see if one of those gives you the same results you see in the car.</p></blockquote><p></p>
[QUOTE="mwolson, post: 11777694, member: 16006"] If you can, run the test I described in my write-up. If, for some reason, something broke in the tach, it will read 3600 RPM rather than the 1800 it should. On the PCM side, I can't figure out how the PCM would put out a 2X tach signal, unless there is noise in it. There is some adjustabillity in the tachometer calibration adjustment pot on the PCB of the tachometer circuit, but it is not enough to double it. However, there is a ground trace on the flex circuit on the back of V8 clusters that is cut on the V6 clusters. If that ground trace is not making contact for some reason, it would turn your tach into a V6 tach. If you add the adjustability of the pot to that, you might be able to get to a 2x difference. (Your tach is acting like a 4 cylinder tach for some reason.) I assume you are running the Cobra PCM, not the Mk8. If you run the test in my writeup, run the test for both the V8 and V6 tachs to see if one of those gives you the same results you see in the car. [/QUOTE]
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Tach reading double?
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