Jump to content
HybridZ

240z tach driver


davek

Recommended Posts

Has anyone on here tried this tacho driver. Any success? I nearly have all the components and am close to give it a try.

dinoplex.org/tachoconversions

 

Or--has someone derived a better way to drive the old 240Z tach with megasquirt?

Thanks

Dave

 

Link to comment
Share on other sites

240Z tachs were different in the early years. They were a current loop style much like a Smith's.

 

Around 1973  they changed to an RPM sensing type which should work with a Mega Squirt or any other ignition box with a Tach output. You may or may not need a Tach adapter on the later styles.

 

Part # 24855-E8200 ( before 08/72 )  is current sensing type which is difficult to get working with stand alone EFI systems or aftermarket ignition boxes. Anything after that should work. 260Z and 280Z Tachs for sure are RPM sensing.

 

http://www.carpartsmanual.com/datsun/Z-1969-1978/electrical/meters

Edited by Chickenman
Link to comment
Share on other sites

My Z is a 73. I have not tried connecting the tacho wire from megasquirt to the tach yet. I just assumed it would not work. I haven't removed the tach to see if it has the single green wire signal wire or not.

I did buy a 76 tach and was told it is a working unit. Well what do you know? It does work when powered to battery and signal from Megasquirt.

Using an analog multimeter wouldn't I see a flicker on the megasquirt tacho wire at 900 rpm? That's 15 pulses per second? I see a rock solid 13v.

fishing guys just fishing.

Link to comment
Share on other sites

Megasquirt is open source, I believe.  Some hot rodder/coder out there could probably figure out a way to drive two ignition types at once.  One for the plugs and one for the 240Z tach.  The "adapter" might just be a separate ignition coil that discharges to ground, dedicated to the tachometer.  It would look like a plain old points ignition system to the tachometer.

 

A person could even run a distributor just for the tachometer, if they had a crank trigger for the plugs.  It would have no plug wires or coil wire.  The coil discharge wire would be attached directly to ground.  Actually, you wouldn't even need the cap, except to protect the points.  You could build a smaller cap for that purpose.  The distributor and its points would just be an RPM counter for the tach.

Link to comment
Share on other sites

Megasquirt is open source, I believe.  Some hot rodder/coder out there could probably figure out a way to drive two ignition types at once.  One for the plugs and one for the 240Z tach.  The "adapter" might just be a separate ignition coil that discharges to ground, dedicated to the tachometer.  It would look like a plain old points ignition system to the tachometer.

 

A person could even run a distributor just for the tachometer, if they had a crank trigger for the plugs.  It would have no plug wires or coil wire.  The coil discharge wire would be attached directly to ground.  Actually, you wouldn't even need the cap, except to protect the points.  You could build a smaller cap for that purpose.  The distributor and its points would just be an RPM counter for the tach

 

 

If it is the later tach that is not current sensing, then you can also build a little circuit with an inductor (coil) from any regular automotive relay. I outlined the process I believe in the RB forum on getting stock gauges to work. Some people have gotten the tach to work with just a 12v square wave (like megasquirt would give you) as well.

 

First let everyone know what style tach you have. getting the current loop sensing one to work could be trouble though.

Mark

Link to comment
Share on other sites

The attachment that the OP put on there shows  CB for the current type tach. I think it would be easier to try and get a 73 or later to work. I didn't think the later tachs like the 280s mount in to the dash right. So maybe the 73 is your best option?  

Link to comment
Share on other sites

Got the 8920 tach adapter to work with my MS3. The key for me was to wire DIRECTLY off the tach plug in the back. I cut the green/white and black/white wires at the connector and ran wires from there to make the tach loop. I then wired exactly per instructions. I think the path of current takes to many detours in the harness to try and pick up the tach from under the passenger side wiring.

Edited by madkaw
Link to comment
Share on other sites

Good to here it's possible madkaw. What year is the tach you got working?

On the old tach black/white is the coil wire I think, what is the green/white wire you refer to? Like Isaid I don't have my tach out of the dash. I'm working off internet pictures of old tachs and the 76 tach on by bench.

Link to comment
Share on other sites

Hey Madkaw.  I've been having issues with my early tach (Similar build date as you) and my ZX distributor.  I noticed an 8920 is available locally, I may pick it up if you've had success with it.   Better yet, I have a MS2 on my desk awaiting install.  Did you have any luck with the 8920 prior to MS as I believe you were running a ZX distributor as well.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...