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Old 07-23-2010, 04:57 PM
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Tach stopped working with MSD

I heard a repetitive snapping sound from the MSD 6a box which was mounted in the firewall while my car was idiling. My then working tach and my car dash tach now only reads 500 rpm. If I pull the tach wire out of the MSD box they both drop to zero, so it can't be the tachs. My question is,
I will try the volt reading on the tach output which should read between 3 and 5 with the car. But could this also be the distributor, and how could I check to see if that is faulty?

As a side note. during the snapping sound I found my braided vacuum hose from my distributor very near or touching the positive side of the coil. Could this have fried something?
If my cars runs great and is not affected by this, could I reasonably assume it will run until I purchase another 6a box?
Thanks
\Lou

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Old 07-23-2010, 07:08 PM
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there is a forum you can go to to help you diagnose the issue. just type in msd 6a troubleshooting into your browser os search engine and it will take you there.
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Old 07-23-2010, 08:14 PM
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I believe your tach has been zapped!
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Old 07-24-2010, 06:14 AM
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Naw the tachs are probably ok he said BOTH tachs are reading 500 rpm so it is more likely the tach output from the msd box. His question was speculative wether or not it would just quit without a moments notice.Good question.
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Old 07-24-2010, 06:19 AM
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Quote:
Originally Posted by Cobra720
I heard a repetitive snapping sound from the MSD 6a box which was mounted in the firewall while my car was idiling. My then working tach and my car dash tach now only reads 500 rpm. If I pull the tach wire out of the MSD box they both drop to zero, so it can't be the tachs. My question is,
I will try the volt reading on the tach output which should read between 3 and 5 with the car. But could this also be the distributor, and how could I check to see if that is faulty?

As a side note. during the snapping sound I found my braided vacuum hose from my distributor very near or touching the positive side of the coil. Could this have fried something?
If my cars runs great and is not affected by this, could I reasonably assume it will run until I purchase another 6a box?
Thanks
\Lou
Chances are the vacuum hose ( braided one you mentioned) probably didnt hurt anything although shorting out all that voltage can cause voltage spikes that wreak havock with some components. If you suspect it shorted out re route it a little neater... after all neatness counts at the shows too. something is wrong with the box for it to make a snapping sound. I would suspect it is not going to work long.go to that MSD webpage I told youabout and see if that helps. Good luck
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Old 07-24-2010, 08:41 AM
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Is this a new build or a car that you have been driving for a while? If a new build and with some brands of tachometers you will need an MSD Tach Adapter for the 6 series modules. I have VDO gauges and have to use one. See this photo (sorry - it shows upside down ). The adapters are about $59 at Summit and there are two versions:



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Old 07-24-2010, 09:11 AM
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The "+" terminal of the coil sees 12VDC nominal. Intermittent shorting the terminal could have caused an ignition miss or degraded performance but probably nothing else unless it was a hard, continuous short to ground- which you'd have known right away.

Don't let form screw up function: Treat the braided vacuum line and ANY braided lines like you would any bare, uninsulated conductor- keep it away from electrical components where there's a chance of shorting to ground or cross communication between circuits.

Last edited by cobalt327; 07-24-2010 at 09:20 AM.
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Old 07-24-2010, 10:32 AM
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Thanks as always Cobalt.
I tested 4.05v at the msd box and 3.77v at the dist. at idle. I'm lost at this time, that snapping sound at the box is the indicator for something but I can't put my finger on it. I know there is a transformer in the box and maybe diodes and I wonder if the rpm (tach) side is separate, as the car runs like always.
I'll call msd tech
Lou
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Old 07-24-2010, 10:35 AM
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Thanks guys for the responses.
This combination has been running flawlessly for some time.
Lou.
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Old 07-24-2010, 10:45 AM
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Lou, you can send the box back to MSD for repair. They'll contact you w/what they fine before doing the repair w/any charges. Might be cheaper than a whole 'nuther box- if you can spare the car during peak driving time, that is!

INFO- "If you have any questions concerning your MSD, call our Customer Support Department at (915) 855-7123, 8 - 5 mountain time."
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Old 07-25-2010, 06:50 AM
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I found out that Autogage tachs need an adapter, although some say they can get their Autogage tachs to work without the adapter. Mine never had an adapter and worked . I found out and concluded that it is possible due to minor and different fluctuations in voltage, my tach could have become incompatible with the magnetic output voltage and NOW needs the adapter.
I spent all day at the beach thinking about this . I hope I'm on to something.
When the adapter comes in I will post my findings.
Lou
Cobalt, you are correct, it is prime driving time for my Cobra roadster/dragonsnake. I'll by another ANYTHING at this time and keep the other for a spare.
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