HEI Tach issue - ClassicOldsmobile.com

HEI Tach issue

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Old July 17th, 2016, 01:34 PM
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HEI Tach issue

Hello all,
My name is Jerry and I'm addicted (to my 69 442)
I am the new owner of my 2nd 69 442. .
The previous owner had informed me that he had a problem with the Tach reading high at cruise RPM, so he attempted to install a signal filter to correct the issue. Well as to be expected, that didn't work out so well as the tach now reads very low(400 rpm or so at idle). Car has HEI ignition and I haven't taken the time to check out the problem as of yet(to busy admiring and having fun).
If any of you folks can give me any advise on what to look for to correct the problem I would be forever grateful. I cut open the filter wiring. Filter appears to be an Auto Meter # 9116. filter came with 4 wires attached: 2 black, 1 in & 1 out. Other side, 1 green & 1 purple(in and out NOT labeled as such)on side with Purple & black shows they attach to: P= to coil neg, blk to ground. Other side of filter.
green to indicator , blk to indicator. Other side, Green to tach output @ dizzy blk to groung @ firewall
.Car has GM type HEI dizzy
Previous owner who installed filter said that with with Blk connected to ground with wires on coil side he seen smoke, so he disconnected the blk wire mentioned and no more smoke but now Tach reads very low 400rpm @ idle. I have only removed heat shrink at present and looking for advice on where to go now.
Sorry for the long post, any help much appreciated
Jerry
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Old July 17th, 2016, 01:40 PM
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Link to Auto Meter schematic for above post:http://www.autometer.com/media/manual/2650-1549.pdf
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Old July 17th, 2016, 02:16 PM
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What does the tach read at idle without the filter? There is an adjustment on the back of the tach and they do go out of adjustment over time.
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Old July 17th, 2016, 02:23 PM
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I haven't disconnected the filter yet. Tach is an original tic toc tach. I may remove filter later. Previous owner installed filter due to high reading at cruise power. That's all I know about it at this time.
Thanks for the reply
Jerry
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Old July 17th, 2016, 04:08 PM
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I removed the filter and now the Tach appears good at idle. I'll get the car out tomorrow and check Rpm at cruise speed
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Old July 17th, 2016, 07:12 PM
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Make sure to compare it to a known good diagnostic tach. I used one in a digital VOM to compare and adjust the one I had in my 1970 442.
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