280Z tachometer problems with a ZX (E12-80) ignition module

[Av8ferg]

Well, I didn’t Know I had a 1 ohm coil until I stated digging in my parts bin. 1 ohm coils didn’t seem very common in the marketplace as 1.5 ohm. So on MSAs website they recommend a 1.5 ohm coil. Also the Tachometer seems more stable on the 1.5 ohm coils . Smoother and less erratic…from my experience. Now I just need to make sure I don’t get problems at high rpm with this higher resistance coil. Will do more testing.

[Emerald280Z]

Wanted to revive this to see if you all can help me with my tach. Did 280ZX upgrade to my 280Z. Now it reads well at idle then if I blip to throttle it goes to 0. Eventually it goes up but bounces around. I’ve tried a new tach and it does the same. Using a FAST PS40 1.4ohm resistance coil with matchbox distributor. 

[SteveJ]

34 minutes ago, Emerald280Z said:

Wanted to revive this to see if you all can help me with my tach. Did 280ZX upgrade to my 280Z. Now it reads well at idle then if I blip to throttle it goes to 0. Eventually it goes up but bounces around. I’ve tried a new tach and it does the same. Using a FAST PS40 1.4ohm resistance coil with matchbox distributor. 

Did you remove the TIU from the car?  Do you still have the resistor (not the ballast resistor) in between the tach and the ignition circuit?

[Emerald280Z]

Thanks for prompt reply. I soldered in a 1/2W 10k resister off coil to tach. My car has been converted to carbs prior to me and a lot of wiring is from that conversion. Here is a pic of area of TIU. 
Thank you for your help. Been chasing this a while and am stumped and also limited with time and knowledge. 

[SteveJ]

1 minute ago, Emerald280Z said:

Thanks for prompt reply. I soldered in a 1/2W 10k resister off coil to tach. My car has been converted to carbs prior to me and a lot of wiring is from that conversion. Here is a pic of area of TIU. 
Thank you for your help. Been chasing this a while and am stumped and also limited with time and knowledge. 

 

So if you converted to a ZX distributor, why did you leave the TIU in place? It should go bye-bye.

Also why did you solder in a 10K ohm resistor? The value should be 2.2K ohm if I remember correctly, though on a Google search @Zed Head gave a value of 2.3k on another thread. Double check the FSM. I know it has the value.

[Emerald280Z]

I got that info from cali Datsun as to help with jumping tach. 
 

when I remove TIU does anything go in it’s place or simply unplug it?
 

thanks for prompt replies 

 

[Zed Head]

Av8ferg solved his problem in this thread by swapping coils.  Not really clear why that worked but it did.

Like SteveJ says though, the old TIU should be completely disconnected.  The wire to the tachometer is a branch off of the blue wire from the engine bay.  It does not run through the old module.  And the 2.2 kohm resistor is in-line buried in the wiring on the way to the tachometer.  You should be able to just connect the blue wire in the engine bay to the coil negative, disconnect the old module, and have everything working correctly.

[SteveJ]

Just to complete the explanation, the TIU does the same thing as the "matchbox" module on the ZX distributor.

Several years ago, a friend did a ZX distributor conversion on a 260Z and brought the car to me because it wasn't running right. The first question I had was, "Did you disconnect the TIU?" After he unplugged it, the car ran like a scalded dog.

Verify that the stock resistor is still in place.  It should reside in the passenger footwell and plug into the wiring harness.

[Zed Head]

13 minutes ago, SteveJ said:

Verify that the stock resistor is still in place.  It should reside in the passenger footwell and plug into the wiring harness.

 

It's a lump in the taped up harness.  Like a frog in a garter snake.

[Emerald280Z]

Appreciate it and thank you both.  Will get it out and report back. May take some time to get to it. 

[Zed Head]

6 minutes ago, Emerald280Z said:

Appreciate it and thank you both.  Will get it out and report back. May take some time to get to it. 

There's no need to get it out.  Just verify that the lump is there.  If the tape is unmolested you migth as well leave it.

Remove all of the existing wrongness and see where you're at.

[Emerald280Z]

Gonna remove tiu and check for resistor