Getting standard 240Z tacho to work with aftermarket computer?

[Scando]

Hi folks

 

Just switched to a computer which controls fuel and ignition as opposed to the old computer which was fuel only.  I was wondering if anybody has the standard tacho working off the signal supplied by an aftermarket computer?  If so, how did you do it?

 

Also tried hooking it up off the coil the same as it was with the old computer and it stops the car when it's connected.........I did a search and found the threads with the diagrams showing how to get the tacho to work with an electronic distributor.  I'll study them and have another go at doing it off the coil but it would be great to get it working from the computer signal.

 

Thanks

 

Shane

[NZeder]

I had my tach changed internally to be more like a modern tach. The zed tach is a copy/license of the smith tach so I took mine to a smith agent who installed a common jag upgrade (good news for you these kits are made in Australia ) this changed the tach from the old inductive pickup on the + side of the coil to the modern - side pics and thus should work with any ECU than output the signal.

[Scando]

Thanks NZeder.  Do you remember roughly what it cost?  I don't really use the tacho so I don't want to spend a fortune.

 

I might just try to find a cheap aftermarket one a similar size and try to fit it in the original spot.

[Zeddophile]

The other trick used is to use the signal from the ecu as the earth on the switching circuit (energising winding) in a relay, with 12v fed into the other pin.  Usually the tacho wire would be spliced into the wire back to the ECU (negative side), but in this case you'd try splicing it into the 12v feed, I guess?  Better check with the ECU manufacturer that the tacho output pin can handle sinking the current required to turn a relay on though - its not a lot, but if the ecu doesn't have powerful enough transistors on that pin, it could possibly cause damage to the ecu (or it just won't work!).

 

This is how I have the tacho going in my Alfa, with the relay trick.  Only thing is, its a good idea in a road car to open up the relay and rip the actual contacts out, otherwise the highspeed whir from the contacts opening and closing will drive you bats**t!

[NZeder]

I had 2 done at the same time - a 240z one and a 260z. The 240z well it went into my 240z (now sold) my 260z well that is just sitting on the shelf -  I will not be using it now that I have a new 10K with build in shit lights. Cost was $250 for the both (and that is NZ play money to use guys) So about a C note I would guess locally for you guys. I would google Jag smiths tach fix/upgrade or the like and see what comes up.

[.]

I put the mechanism from a 280zx in the housing from my 240z. Works a treat and didn't cost a cent.

[NZeder]

I put the mechanism from a 280zx in the housing from my 240z. Works a treat and didn't cost a cent.

That soulnds like an excellent idea - well done that man - were was that idea ......4 years ago I had my brain in reverse for sure.

[Scando]

We ended up getting the standard tacho working by accident!

 

We've spent the last couple of weeks chasing a bad missfire at around the 4,000rpm mark with the new computer.  We went to the extent of grafting a complete RB30 distributor onto the L28 because we thought it was getting a bad trigger signal and this still didn't fix our problem.

 

Then tuesday night we got it to go up to 6,000rpm with no missing..........tried again a few minutes later and it missed again.......then one of the guys realised it was only when the timing light was being used that it would rev happily.  We considered getting the tape out and finding a spot in the engine bay for the timing light 

 

In the end we just powered the coil from the original power supply which runs through the tacho instead of the power supply from the computer.  Problem fixed and my tacho works

[zed240au]

i bought an aftermarket tacho and fitted it to 240z housing and face plate works fine

[.]

hmmmm. Brain wave.

Add a timing light in the engine bay. Add a video camera pointing at the pully. Then add a TV in the cabin so you can see what the timing is doing while driving. Brilliant!!! I don't know how I survived without it.