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Help...280zx e12-80 and MSD 6AL to a 240Z


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My son has a 1973 240z with stock ignition, weber 40's and headers. We have purchased a MSD 6AL, Blaster 2 coil, and 1979 280Zx e12-80 distributor

Does anyone have a good wiring diagram to use? After looking at the directions and searching the internet there seems to be a few ways to do this and we would like the Tach to work. It sounds like some folks use the 8920 tach adapter and some don't.

Any help would be appreciated before we tackle the job.

Thank you.



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Can't tell you how to make sure that the tach works but I do know that you can drive the car while you try to figure it out.  The ignition system will work fine even if the tach needle doesn't move correctly.

I would look at the wring diagrams for the two cars and just figure it out if you can (http://www.classiczcars.com/files/).  Other people's wiring schemes can get weird.  It's just a path for current to flow through the coil, with a circuit breaking mechanism (points or module) along the way.  The Atlanticz procedure seems to work well although it is for replacing an electronic module.  Note the recommendations on checking the internals of the distributor.  If it's not a recent reman there may be rust and problems inside.





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That's a good point.  I overlooked the 6AL part.  The other view would be, you don't need the 6AL with the black box/module.

That ZX distributor should really be looked over either way.  They're not very durable, the stator magnet tends to break and the shaft bushings tend to wear out.  Along with the usual rust on the breaker plate bearings.  

Overall, it's kind of a complex swap, lots to worry about and problems to solve.  Pretty sure I've seen problems with the 280Z tachs and the MSD boxes also.  There are probably more posts out there on the internet about MSD boxes and Z car tach problems than any other ignition system.

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I bought a Remanufactured 1979 280zx dizzy from Rock Auto and it looks ok.

I was going to leave the e12-80 module on it at which point you hook it up according to the points MSD 6al instructions.

If you remove the e12-80 you use the violet and green wires and hook it up using the crank fire/magnetic dist instructions.....what are the benefits of going this route?

It looks like I need the 8920 tach module to get the tach working.

MSD said I could try hooking the tach up to the white trigger wire on the C on the module....I assume he was talking about the Black White tach wire?

Calling them again.





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from what I've read over the years the MSD guys will only tell you what should work.  But not what does.  They don't know, they're just reading the same instructions you are.

Here's a collection from the site.  The one where the guy says he gets tach action but it's not right kind of indicates that some signal-conditioning would help.  The current passing through the tachometer is either too noisy, or too high or too low, I would think.  The tach adapters that MSD sells are probably just resistors or capacitors or a combination of both, packaged up to look nice.  

Good luck.  As you can see, many efforts just fade away with no resolution.






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Just fleshed out a thought on why the 240Z tach has so many problems with the ignition modifications.  Maybe SteveJ or CO or one of the other engineering types can ponder it.  The 240Z tach is designed to count current pulses, in series with a "6 volt" ignition system.  When people upgrade to high energy (high current) systems, like the MSD or the ZX module, the current is too high for the tachometer.  The only way to bring the current down to a useful range would be to throttle the current and go back to a "6 volt" type system.  This is why the Pertronix system works but the high energy systems don't.

Maybe there's a way to bleed some current through the tach on a parallel. branch.  High current to the coil, low current to the tach.  Not sure how that could be accomplished, but it seems like it should work.  Maybe two ignition (circuit breaker) modules, one for the tach and one for  the coil.

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What i know there are no benefits of useing or not useing the zx module (I don't use mine)with the msd 6al but by not useing it you take out one thing that could cause problems. 

Edited by moelk
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One big difficulty in working with the MSD box is that there are no good specs on what the wires and adapter actually do.  Vague words about tach triggers, and outputs, and adapters.  If they could just tell somebody something useful like "the gray wire produces a 12 volt square wave of approximately ___ amps for each trigger from the distributor" and "the 8920 adapter is a ballast-type resistor of ~ ___  ohms at ambient temperature" then you could match the specs to the original 240Z system specs.  

They do say that the Gray wire produces a 12 volt square wave of 20% duty cycle.  No info on current though and there doesn't seem to be a fuse.

If you can find anybody at MSD that can tell you how these adapters actually function and more about the Gray wire then somebody out here could probably figure out how to make it work on the 240Z.  There are probably guys that can use that 20% duty cycle square wave info and get it done without the 8920.  MSD would probably sell more boxes but fewer adapters. 

Good luck.  Here's more info from the web.




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If you do use the MSD adapter with their scheme you might insert a potentiometer in between the 8920 and the tach.  That will allow you to control current through the tach.  As it stands the adapter might just be a wide open low resistance path to ground.  Who knows.  

Add the pot., and just open it up until the tach starts working.  Wouldn't be a surprise either if you put the old ballast there and it worked.

The adapter wiring looks a lot like ignition module wiring.

current control.PNG

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A followup on my last comment.  I think that you could use a $20 GM HEI module and that 12 volt square wave on the Gray wire, with the old ballast resistor to modulate current and get the tach to work.  That 8920 adapter has to be working just like an ignition module.  It triggers from the Gray wire square wave, and lets current flow to ground just like an ignition module.  

The HEI module is often used in place of the 280ZX turbo ignitor, which is triggered by a square wave.  At least you know that it passes ~4 amps, has current control, and won't short.  It's a known quantity, unlike the mysterious 8920 adapter.


Sorry Parkstos, your head is probably about to blow up.  One thing you could do is wire it up using just the ZX module.  The MSD box can be added later after you get more information.  It's an add-on, for what you have, not a requirement.  The engine will run very well with just the ZX distributor.  The MSD box advantages are more for low RPM, somewhat "dirty" engines, like with a big cam and carbs, that tend to load up the plugs.  You don't really need the MSD box..  

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