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Old 04-16-2010, 06:16 PM   #1
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Tachometer RPM Jumping Up and Down / Fluctuating

Sup all,

Having a little problem in my 82. The tach jumps around at high rpms and sometimes low. You can see it in the video. I replaced the rotor yesterday after having the car not start. Turns out the rotor contact was broken, screws were off and pieces were just lying around in the disty. When I replaced the rotor, is there supposed to be a little play in it side to side? Like the inner shaft moves slightly. The check engine light blinks randomly at higher speeds so it is missing.

Wires and plugs have been changed. But I'm guessing I was driving around with a broken rotor for a while with the engine missing, so would it be possible that a plug is bad? Or is it something else ignition related? It was jumping around more when the broken rotor was in there and I didn't know.

http://www.youtube.com/watch?v=GzUKCCuZwRs

Any ideas?
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Last edited by KnightmareCS; 04-16-2010 at 06:20 PM.
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Old 04-16-2010, 08:48 PM   #2
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Re: Tachometer RPM Jumping Up and Down / Fluctuating

it sounds like your ignition control module, if you have replaced your distributor with a remanufactured one or even some after market ignition coils will cause that jumpy tach.
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Old 04-16-2010, 09:24 PM   #3
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Re: Tachometer RPM Jumping Up and Down / Fluctuating

Your tach is just screwed,i think.My stock tach shows an idle speed of 4,500-5 k and hits 7 k pulling out of a parking spot lol.it happens to alot of the stock tachs.Either buy an aftermarket one if you think you need an ultra precise one or try the tech articles on the main page.I believe there is a article on how to repair the stock tach.
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Old 04-16-2010, 09:45 PM   #4
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Re: Tachometer RPM Jumping Up and Down / Fluctuating

I used the info on tech articles here. Mine works great after I repaired it.
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Old 04-17-2010, 05:05 PM   #5
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Re: Tachometer RPM Jumping Up and Down / Fluctuating

I don't think it's the tach. It idles at the right mark (verified with timing light). Only up top when it starts missing does the thing jump around. I'll do some research on the ICM and maybe try swapping with my 83 to see if that makes a diff. Thanks so far guys!
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Old 04-17-2010, 09:46 PM   #6
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Re: Tachometer RPM Jumping Up and Down / Fluctuating

Check ALL the grounds, I've seen bad grounds cause jumpy tach's more than once. I'd start with the instrument cluster and where it grounds at.
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Old 05-06-2010, 06:16 PM   #7
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Re: Tachometer RPM Jumping Up and Down / Fluctuating

Problem fixed. Had a clutch problem and changed it. Doesn't jump anymore.
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Old 05-29-2010, 10:04 PM   #8
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Re: Tachometer RPM Jumping Up and Down / Fluctuating

mines doing the same thing but I have a new clutch distributer and rebuilt engine. Are you sure it was the clutch? how would that cause a jumping tach?
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Old 06-01-2010, 09:01 AM   #9
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Twittery Tach

A clutch would have to be slipping or chattering to show on the tach, in which case the attention would be drawn to the clutch and having that repaired.


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Old 06-01-2010, 09:01 AM
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