Will any tach work with an MSD?

[68R/T]

My Hemi Coronet has an MSD, I don't know which one because it's painted over. Anyway, I got a used tach and it doesn't work. It could be that it's junk, but I was wondering if the MSD might need a specific tach. :huh:

 

[69.5CUDA]

no but i remember you have to either run it off the tach wire on the msd(not the coil)some its a wire some its a small black recessed spade(depending on year/model) or you had to run some kind of msd filter on the coil to the tach....its been ages since i had to mess with one of my msd's

 

[68R/T]

I found a ton of online schematics. One shows a tach output terminal on the module;



Another schematic shows the use of a tach adapter;



I guess I need to move the tach wire to the output terminal and see if it words. If it doesn't I need to get an adapter.

 

[Dr.Jass]

It seems to me that if you wire a tach to coil (-) with an MSD you get a high reading, due to the multiple-spark discharge for which it's named: "Jeez, it doesn't sound like a 2,500RPM idle..." This is true of any CDI ignition; the multiple sparks at low RPM are necessary for the capacitive-discharge section to live more than 10 seconds at normal low-RPM coil dwell times. Many older tachs will need the adapter; most musclecar-era factory tachs will. The MSD's tach output is, if memory serves, a 12V square-wave signal, Older tachs connected to coil (-) also see a 12V square wave, but they work by reading the high-voltage flyback at the coil terminal when the field collapses (believe it or not, it's around 400V for a bazillionth of a second). Generally speaking, if it's a quality aftermarket tach like an S-W, VDO, or AutoMeter, it shouldn't need the tach adapter unless it's old enough to require use a sender--but you've got to know that you're using a good tach in the first place.

Start with a known-good tach connected to the output on the MSD. It won't hurt anything if it needs the adapter, it simply won't work. I'd suggest verifying the function of the tach you bought--and/or any other you might use--on the See-Dan or the wagon. Of course, I'm assuming neither of those cars has a CDI box. Hell, you can verify function on Miss Ugly if you want, but the readings will obviously be wrong.

 

[68R/T]

Seeing as it's already install I think I'll move the pickup wire from the coil to the MSD output and see what happens. :hmmm:

 

[Dr.Jass]

You installed a used tach before you even checked to see if it worked?






Seriously, if you got no needle movement a-tall from it connected to coil (-) the odds are pretty good it's NFG. Does the needle move at all when you turn the key to run? If not, you likely need to find another tach.

 

[68R/T]

I moved the sensor wire from the coil to the MSD tach sensor connection, still no-go. Or maybe this answers my question, from the MSD web support site, when & which tach adapter to use;

AFTERMARKET TACHOMETER WHITE WIRE TRIGGER MAGNETIC TRIGGER CONNECTOR
AUTOGAGE 8910 8920
AUTOMETER NONE NONE
FORD MOTORSPORTS NONE NONE
MALLORY NONE NONE
MOROSO NONE NONE
STEWART (voltage triggered) 8910 8920
S.W. & BI TORX NONE NONE
SUN 8910 8920
VDO 8910 8920
AMC (JEEP) 8910 8920
CHRYSLER 8910 8920
FORD (voltage triggered) 8910 8920
GENERAL MOTORS Bypass In-Line Filter Bypass In-line filter
IMPORTS 8910 8920
Note: On the list above, the trigger wire on tachometers that are marked NONE may be connected to the Tach Output Terminal on the MSD 6 Series Ignition Unit using the supplied Female Fasten Receptacle.

I need to get an MSD 8920 Tach Adapter.

 

[68R/T]

Found a deal on the correct MSD tach adapter for my ignition and now tach works. Next step is to figure out how far NOT to rev it. [smilie=f:

 

[Dr.Jass]

Keep it under 7 grand and you're fine.

 

[68R/T]

So far I've found that 6,500 is a good point. :shifty: