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11-29-2010, 04:38 PM | #1 |
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Join Date: Apr 2005
Location: Brookings_South Dakota
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Tach Problems
I just took out a year old aftermarket tach and replaced it with a tach dash. But I realized that the rpm's are off when driving down the highway now. The tach reads about a thousand rpm higher than my aftermarket tach read. I have 4.10 gears with an automatic and now it says I'm doing over 5 grand going down the highway. Is there anything I can do to my tach or do I have to replace it with a new one?
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11-29-2010, 05:35 PM | #2 |
Formerly- 1972SuperCheyenne
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Re: Tach Problems
Your tach dash for a v6 or v8?
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11-29-2010, 06:02 PM | #3 |
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Re: Tach Problems
The tach dash I got came out of a grain truck with a big block in it.
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11-29-2010, 11:58 PM | #4 |
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Re: Tach Problems
What kind of distibutor do you have? Some aftermarket distributors require a tach signal adapter to function with a factory tach, the signal is different for oe vs. Aftermarket!!
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11-30-2010, 03:42 PM | #5 |
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Re: Tach Problems
I have a standard hei distributer, but it has a hypertech coil in it. I'm kind of clueless. The only thing I can think to do is buy a new tach.......
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11-30-2010, 03:56 PM | #6 |
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Re: Tach Problems
Coil shouldn't matter, it's an hei which should put out the right signal, the tach may be for a 6 cyl, it is a GM tach right? if you know 100% it's an 8 cyl tach then it should work. If it is an original tach and it's reading too high it sounds as if you got a 6 banger tach.
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11-30-2010, 06:09 PM | #7 |
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Re: Tach Problems
Okay, well thanx for the information. I'll have to tear it apart this weekend and start looking around for another tach.
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01 Pontiac Bonneville SLE 62 Studebaker GT Hawk 72 GMC C20-327/th350 81 Chevy c10 84 Monte Carlo SS 70 Ford 3/4ton 4X4 Highboy 390/bedhoist 68 Mercury Cougar GT |
11-30-2010, 06:33 PM | #8 |
Roadtrip!
Join Date: Feb 2003
Location: Grand Rapids MN
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Re: Tach Problems
If it is not too faded, there should be a stamp on back of the tach head for 6 cyl or 8 cyl. There is also a small hole that has an adjuster in it. I have heard of people tuning them that way, but i have never done it. Keep in mind, these were never real accurate from day 1. It shouldn't be off by 1000 rpms though. Good luck.
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11-30-2010, 08:47 PM | #9 |
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Re: Tach Problems
ya I couldn't remember so I looked in my pictures I took and it was an 8 cylinder tach. I'll try adjusting it a little to see if it helps, thanx
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01 Pontiac Bonneville SLE 62 Studebaker GT Hawk 72 GMC C20-327/th350 81 Chevy c10 84 Monte Carlo SS 70 Ford 3/4ton 4X4 Highboy 390/bedhoist 68 Mercury Cougar GT |
11-30-2010, 09:25 PM | #10 |
Tot Roddin'
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Re: Tach Problems
I thought there was a different wiring harness for a standard coil vs. HEI. Am I wrong?
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11-30-2010, 09:52 PM | #11 | |
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Re: Tach Problems
Quote:
Posted via Mobile Device Last edited by PCHRODS; 11-30-2010 at 09:54 PM. |
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11-30-2010, 10:13 PM | #12 |
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Re: Tach Problems
You said you have 4.11 gears and an automatic; I am going to guess a th350. You can always do the math and find out if it’s the tach dash that’s off or the old one, maybe a bit of both.
Check out this link and enter your information and you'll get your correct RPM and Speed, http://www.pszweb.com/car/gears.htm
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12-01-2010, 04:38 PM | #13 |
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Re: Tach Problems
well thanx for the tips guys, the only thing I can think of is that I didn't buy a harness for the tach. It had the female connector on the back of the tach when I got it so I just made a harness for the tach using some regular wire hooked up to the distributer and fuze box. I didn't think this would affect it since it's still getting power, what do you guys think?
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01 Pontiac Bonneville SLE 62 Studebaker GT Hawk 72 GMC C20-327/th350 81 Chevy c10 84 Monte Carlo SS 70 Ford 3/4ton 4X4 Highboy 390/bedhoist 68 Mercury Cougar GT |
11-30-2010, 09:57 PM | #14 |
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Location: Huntington Beach, CA
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Re: Tach Problems
Another thing to look at!! Make sure the coil is getting a full 12v alot of time on originally equipped points vehicles they had a resistor wire on the coil feed that dropped the voyage down to 7 volts, you disnt say anything about sputtering issues so this has probably been long sense removed! Just a thought!!
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