Tach Problem!
Thread Starter
Instructor
Joined: Jan 2007
Posts: 109
Likes: 1
From: Huntsville, AL
Tach Problem!
I have a Sunpro Super Tach ll with the corvette face in the cluster of my car. I purchased this when I had the cluster refurbed at Joe Ray Parts in Arkansas. Comparing the tach with an outboard tach (Auto Meter) the tachs both idle just the same. When I accelerate, the Sun reads more than the Auto Meter. At 5000 rpms showing on the Auto Meter, the Sun tach reads 7000 rpms. Does anyone know a fix for this, and why I am getting these readings. I am confident that the Auto Meter is correct because of the Calculations at every speed line up with what the online calculator says they should read. (formula with the tire size, diameter, rear end ratio, etc. I have had the tach out of the car several times to ensure that I had the correct switch setting for 8 cylinders on the back of the tach. (switch for 4, 6, or 8 cylinders)
Joe Ray and others use these tachs on other cars, but usually with a Dakota Digital interface, which I do not have, and after speaking with them, (Dakota Digital) They say that their interface will not fix my problem because of both tachs reading the same at idle speed. (900 rpms) I am using an MSD Distributor with a Master Blaster Coil, and NO MSD box.
ANY IDEAS?????
Joe Ray and others use these tachs on other cars, but usually with a Dakota Digital interface, which I do not have, and after speaking with them, (Dakota Digital) They say that their interface will not fix my problem because of both tachs reading the same at idle speed. (900 rpms) I am using an MSD Distributor with a Master Blaster Coil, and NO MSD box.
ANY IDEAS?????
Race Director
Joined: Feb 2004
Posts: 11,030
Likes: 2,587
From: Del Boca Vista FL
It's been a while since I used a Sun tach in anything. Does the Sunpro use an external sending unit or is it internal? If it is an external try swapping a different sender into the system and see if that might be the problem.
Rich
Rich
Thread Starter
Instructor
Joined: Jan 2007
Posts: 109
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From: Huntsville, AL
I am assuming that it is internal. The tach has a Positive, Negative, and a green wire that goes to the negative side of the coil. I have never heard of a sender for a coil, but what do I know??? Thanks for your response!
Race Director
Joined: Feb 2004
Posts: 11,030
Likes: 2,587
From: Del Boca Vista FL
Dan: Sounds like yours is internal. Old SUN tachs utilized a divorced sending unit that mounted away from the tach head and you ran a lead from the coil to the sending unit and another lead from the sending unit to the tach head.
Sorry I don't know more about it.
Rich
Sorry I don't know more about it.
Rich
Thread Starter
Instructor
Joined: Jan 2007
Posts: 109
Likes: 1
From: Huntsville, AL
thanks for your input anyway.....hopefully I can resolve this stupid issue! I am wondering what the difference in the Auto Meter tach, which works perfectly, and the Sunpro....strange, huh?
Burning Brakes
Joined: Dec 2004
Posts: 800
Likes: 3
From: Idaho
Danny
I have the same problem on my car and I have several theories on whats wrong. First off I adapted a Auto meter electronic tach into my stock dash, the Auto meter had a 8,000 rpm sweep and my stock tach face had a 7,000 rpm face. I figure the 1,000 rpm difference had to go some where, and I think it is divided up throughout the whole 7,000 range as my tach is 400 rpm's slow at about 4,500. Both the altered tach and my alternate tach source Idle at the same rpm, but the dash tach starts to lag behind as rpm's go up.
Second, the stock tach face is 5" in diameter and the Auto meter is
3 3/8", so it's my belief that if the band sweeps are not printed in the same arc, this could add to the problem.
I have a 7,000 rpm tach that I will use to replace the 8,000 unit, but thats some time down the road.
I don't know if this helps, but you may want to ask your rebuilder what he used to repair your tach. Also ask him if any of my thoughts make sense.
Good luck
Russ
I have the same problem on my car and I have several theories on whats wrong. First off I adapted a Auto meter electronic tach into my stock dash, the Auto meter had a 8,000 rpm sweep and my stock tach face had a 7,000 rpm face. I figure the 1,000 rpm difference had to go some where, and I think it is divided up throughout the whole 7,000 range as my tach is 400 rpm's slow at about 4,500. Both the altered tach and my alternate tach source Idle at the same rpm, but the dash tach starts to lag behind as rpm's go up.
Second, the stock tach face is 5" in diameter and the Auto meter is
3 3/8", so it's my belief that if the band sweeps are not printed in the same arc, this could add to the problem.
I have a 7,000 rpm tach that I will use to replace the 8,000 unit, but thats some time down the road.
I don't know if this helps, but you may want to ask your rebuilder what he used to repair your tach. Also ask him if any of my thoughts make sense.
Good luck
Russ
Last edited by Russ T Gate; Jan 5, 2009 at 09:11 PM.
Thread Starter
Instructor
Joined: Jan 2007
Posts: 109
Likes: 1
From: Huntsville, AL
Thanks Russ....Mine is reading FASTER than the auto meter tach and gets progressively worse as the rpm rate is increased during acceleration. I called Sun and asked if it could be calibrated, and the service tech there told me no. Guess I will try the Dakota Digital interface and see what happens.
