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echrisconnor's Avatar
 
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Bouncy Tach when hot

New problem. When my car starts to get warm, the tach needle starts bouncing around. Good power, the car runs strong, no stumbling. I haven't checked the ponints gap though.

Any thoughs... CDI, point gap?
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Old 04-17-2006, 08:58 AM
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1 vote for a failing voltage regulator. Common symptom.
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Old 04-17-2006, 09:36 AM
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Clean and adjust the points and if it still persists, check the charging system voltage when the tach is acting up.

JR
Old 04-17-2006, 09:47 AM
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Not wanting to high-jack, but....I get the same problem when the tach gets hot (i.e. direct sunlight on the dash). Also, when I start the car, the red light stays on until I rev to 3000 rpm. Is that an indicator of a voltage regulator failing too?
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Old 04-17-2006, 11:16 AM
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Potentially problems in the VR or charging voltage...? Hmm, so just lay a volt meter on the system while driving and see if I'm getting spikes or drops in voltage? What would make the tach bounce? I'm not having any other electrical issues now.

PS. I'll check points gap first, since that was what I was thinking anyway.
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Old 04-17-2006, 11:23 AM
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I agree with JR. Set the point gap and check it using a dwell meter. Make sure the points are clean (wipe some paper or an index card between them) and check and clean all electrical connections. Finally, check to make sure the voltage regulator is operating correctly. If this doesn't cure the problem, you may want to consider an optical pickup sold by our host here.
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Old 04-17-2006, 11:33 AM
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Is the VR check just to see if I'm getting over 14 volts?
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Old 04-17-2006, 02:04 PM
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Pretty much. If you can, rig up a voltmeter in the car and check to see if the problem with the tach correlates with any over-voltage episodes, as measured by the voltmeter.

I'd still clean and adjust the points first.

JR
Old 04-17-2006, 04:00 PM
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On my 78 SC this problem was followed by a complete failure of the CD unit. I certainly hope it is just a voltage issue and not your CD unit.
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Old 04-17-2006, 04:06 PM
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Pretty common sympton for a faulty voltage regulator, I had the opportunity to experience this first hand last year.
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Old 04-17-2006, 04:48 PM
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Mine has similar but diff sometimes. When it happen, does the engine run diff or just the tach meter bouncing?
My car has similar problem when getting hot, not all the time, but not only the tach meter is bouncing but the engine rev funny too. It acts as you are steping on the gas pedal and let go and keep continue doing it. Tach meter jump up and down between 800/900 rpm to close to 2k rpm.
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Old 04-18-2006, 01:46 AM
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The VR is failing and as it gets hotter both from the engine and overcharging it causes the seat belt light to come on and the tach to bounce in most cases.
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Old 04-18-2006, 05:59 AM
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points point points. this is always what my tach does when points are either dirty or starting to close..
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Old 04-18-2006, 06:21 AM
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Get a Pertronics Ignitor and eliminate the points variable altogether.
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Old 04-18-2006, 06:46 AM
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