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 Post subject: tach signal
PostPosted: Sat Sep 01, 2007 12:30 pm 
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okay, ive had my sunpro tach in the luv for a couple months now, and its always been a bit screwy.

but since i put this new engine in, its gotten really screwy.

what can i do to get a cleaner tach signal from the coil?

it works fine when the engine is idling, but as soon as i tap the gas it jumps up to 3000 and then back down and all over.

would adding a resistor somewhere or something work to clean up the signal?

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PostPosted: Sat Sep 01, 2007 12:40 pm 
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if yours was used like mine I had to find install directions i hooked mine up like it said and no problems, there is always a chance there is a problem with the tack inside wires? just a thought dought this will help but worth a look
http://www.sunpro.com/publish/2004/08/0 ... _16325.pdf

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PostPosted: Sat Sep 01, 2007 12:41 pm 
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Does it have a switch somewhere on it for 8,6,4 cylinders? Just shooting in the dark here.

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PostPosted: Sat Sep 01, 2007 12:42 pm 
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this is prolly a stupid question, but do you have the signal wire hooked to the negative side of the coil?

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PostPosted: Sat Sep 01, 2007 12:45 pm 
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well i know i hooked it up right. i mean theres only 4 wires. and i do have it set on 4 cylinder.

im just trying to find a way to make the needle jump around.

ive checked all my wire connections, and theyre all good. so i dont know what to do.

could it have something to do with my points ignition?

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PostPosted: Sat Sep 01, 2007 12:50 pm 
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do you have an MSD box? they make your tack go wacko, my friends mustang did something similar, the tach would jump around like crazy if he gave it any gas.

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PostPosted: Sat Sep 01, 2007 12:51 pm 
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off road LUVer wrote:
do you have an MSD box? they make your tack go wacko, my friends mustang did something similar, the tach would jump around like crazy if he gave it any gas.


nope, its all stock 77 luv ignition.

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PostPosted: Sat Sep 01, 2007 12:54 pm 
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hmm.. well im stumped then, my tach only jumps when it misses, but it goes right back. Where are you getting power from?

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PostPosted: Mon Sep 24, 2007 3:15 am 
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I had the same problem with my '78 and it turned out that my distributor was really worn out. Got another one for it and the problem went away.

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PostPosted: Wed Sep 26, 2007 4:05 pm 
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Have a Sunpro in mine too.... all was fine with it until I added MSD box & Pertronix setup.
Now it's as screwy as you described, fine at idle and cruising speed. Someone told me to try supression core plug wires, something about the magnetic interference. Haven't messed with it yet.

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PostPosted: Thu Sep 27, 2007 9:40 pm 
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Check all your grounds!!! More electrical gremlins are caused by bad-faulty-rusted ground connections than anything else.

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PostPosted: Thu Nov 01, 2007 5:52 pm 
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check your points! I just bought a sunpro tach and it was jumping all around (not just when I gave it gas), turns out my points had no gap :) I filed the one point flat and adjusted the gap and now it is smooth rpms.


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PostPosted: Thu Nov 01, 2007 6:28 pm 
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I have had very bad luck with the Sun-pro gauges and tach. I had a Sun-poor in my 455 T/A and it was just junk!!!!! I checked the wiring and everything on the face of the planet to try and fix the problem,wires, hei, MSD 6al / distributor. After not being able to shift at the correct shift points for 3-4 weeks and my oil pressure jumping from 10psi to 70psi I decide to dump everything and install Autmeter gauges. I didn't change any of the wiring to the dash just the gauges. next thing I know everything worked like a charm. Strange but the truth.Maybe I had a bad batch but I a firm believer in "You get what you pay for".


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 Post subject: Re: tach signal
PostPosted: Fri Sep 09, 2011 1:07 pm 
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I'm trying to wire up my tach too...

I trust the (-) side of the coil is sufficient for signal, but where can I pull 12v from? Fuse panel...and if so, which fuse?

Or would it be best to run a lead direct to the battery with a in-line fuse?


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 Post subject: Re: tach signal
PostPosted: Sat Sep 10, 2011 9:58 am 
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Location: Upland, CA
You asked about a resistor. Really you would need a condenser (capacitor). Perhaps there are some high frequency signals that are confusing the tach electronics, so adding a condenser to form an RC circuit would at least filter out the high frequency.

Now don't ask me exactly how to do that. I just wanted to let you know a resistor alone won't help, but a capacitor might. You could consider replacing your stock condenser and see if that helps.


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 Post subject: Re: tach signal
PostPosted: Tue Sep 13, 2011 1:12 am 
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Papa G had a good suggestion. Check all the wires especially the ground wire. To those of you with a MSD box, read the directions or call MSD to hook it up, you will find a "tach" connection on the side of MSD 6AL boxes. Good luck


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