MSnS + MSD + Stock Tach

[Phyxius]

Ok, I'm not sure how this works for other year models, but here is how i got it to work for mine ('79).

 

I'm using the MSnS triggered from the stock crank angle sensor on my '81 turbo motor.

 

Getting the MSD to work is simple enough. It can be triggered directly from the MS with no problems...you don't even need the pullup resistor. In this configuration, the stock tach will not work. At least mine wouldn't. It can't be triggered by the MSD's tach output or the coil, so I got the 8910 tach adapter.

 

Ok...here's the tricky part. If you want your tach to work, you have to use either the HEI module or the stock ignition module to trigger the MSD. The MS will trigger the module as before the MSD. You'll hook the wire that went from the module to the (-) terminal on the coil to the MSD white wire and tach adapter as shown in the tach adapter instructions. Basically, the (-) terminal wire becomes the trigger wire, and you use the tach adapter to convert the signal to something the tach understands.

 

I know that's about as clear as mud, so maybe I'll draw a nice diagram later.

[randy 77zt]

doesnt the msd box have a jack in the side with a 1/4 male spade do hook the tach wire to?

[Phyxius]

In this configuration' date=' the stock tach will not work. At least mine wouldn't. It can't be triggered by the MSD's tach output or the coil, so I got the 8910 tach adapter.

[/quote']

 

the msd output wouldn't trigger my tach...as i've heard with many others...

[dapiper]

MSD makes a tacho trigger module for voltaged triggered tachs, essentially an autotransformer and cap to swing the 12V sq wave up to 200V

[HeatRaveR]

Ok...here's the tricky part. If you want your tach to work, you have to use either the HEI module or the stock ignition module to trigger the MSD. The MS will trigger the module as before the MSD. You'll hook the wire that went from the module to the (-) terminal on the coil to the MSD white wire and tach adapter as shown in the tach adapter instructions. Basically, the (-) terminal wire becomes the trigger wire, and you use the tach adapter to convert the signal to something the tach understands.

 

I know that's about as clear as mud, so maybe I'll draw a nice diagram later.

 

When you say I'd need the "stock ignition module" to trigger the MSD, are you referring to the "transistor" that comes with the L28ET mounted next to the stock coil (little metal/black plastic thing about a square inch in size)? I'm trying to figure out if I'm supposed to keep that thing or not when I install Megasquirt.

[zercs280zx]

When you say I'd need the "stock ignition module" to trigger the MSD, are you referring to the "transistor" that comes with the L28ET mounted next to the stock coil (little metal/black plastic thing about a square inch in size)? I'm trying to figure out if I'm supposed to keep that thing or not when I install Megasquirt.

 

Do you mean the ignition module mounted next to the distributor (not the coli)? If you are using an MSD or aftermarket ignition box, it replaces the plastic ignition module on the distributor. If it's a 280ZX distributor, you remove the ign module and tap right into the green and red wires... I think that is what you are referring to.

 

Also, for the tach adpater adapter, I believe you use the MSD 8920 for current/pulse ignitions (for Tachs on the '73 or later) and the 8910 on the old points systems (Tachs that came prior to '73). At least from what I researched... I'm in the process of wiring up my car

[jeffer949]

umm the tach output on my msd 6a s working my tach fine.... i have my msns+extra firing the msd 6a through my vb coil driver. and then just the tach output to my tach. i dont even have the resistor in place. just straight hooked up.. and it matches my ms tach signal. i have upgraded my tach to a 78 unit i believe though

[HeatRaveR]

I do wonder though if a 280ZX's tach would still run properly though, in case there's a difference between the models/years.

[hughdogz]

I do wonder though if a 280ZX's tach would still run properly though, in case there's a difference between the models/years.

 

I just went through this with the Wolf EMS and my '82 ZXT.

 

As mentioned before, there are two types of factory Tachs:

 

-The 240z tachs are current controlled and get their signal from the (+) side of the coil.

-Post-240Z's uses a voltage-controlled tach signal off of the (-) coil terminal.

 

There are three types of MSD tach adapters:

 

8910: Voltage-controlled tach adapter

8910EIS: Current-controlled tach adapter

8920: Can be either voltage or current controlled (depending upon how you hook it up)

Tach manuals clicky

 

If an MSD is not used, you must go with an 8920. If an MSD is used, you can use an 8910 or 8910EIS depending on the application.

 

For a 280ZX, the blue coil (-) wire that feeds the factory tach actually changes to a light green with white stripe after a resistor. I tied into the the light green with white stripe wire right behind the instrument cluster where it comes out of the circular connector block (pin 20). Connect this wire to the output signal of the 8920.

 

You should be able to get away with using an 8910 instead of an 8920 since I could run the factory Tach and FI using and MSD6AL and 8910 tach adapter. The 8910's are ~$35 and the 8920's are ~$55.

 

Hope this helped...