240Z Tach Wiring After 123Ignition Install

[Zed Head]

1 hour ago, PrincePaul said:

No it’s a relay that powers the pump when ignition is sensed via the coil negativ. It does not supply power to the coil. It goes to coil pickup 1 which is the negativ side.

Couldn't really tell from that diagram which is positive and which is negative.  Why would negative or positive matter if it's just sensing power?  (Edit - actually I don't really understand how that device works.  Maybe it's "sensing" sparks?  Current flow?  Whatever it is, the positive side might work the same.  @SteveJ  @Captain Obvious )

If you have another load on the negative terminal of the coil that could screw up your tach signal.  I'd disconnect that before you get too far along and see if it starts working.  I don't know if the condenser will help you with that scheme.

If it fixes the tach problem try using the positive side of the coil for the power signal.  Edit - actually don't try this.  It might be a direct short, depending on how the device works.

Edited June 3, 2021 by Zed Head

[cgsheen1]

2 hours ago, PrincePaul said:

yes the factory unit it all gone also factory ecu. Yeah I’ve the old one from the positiv side of the coil, which I could easily hook up to the negativ side. But I’ll also try removing the fuel safety relay wire just in case. 
 

so 4 possible solutions right now:

1. wire problem, but as it senses something I guess not the case maybe still ground problem. Should be easily checked by direct wiring or probing

2. negative effect from the fuel safety circuit

3. interference where a condenser might help

4. resistor value wrong

i might also try the factory coil which was installed on the car - maybe it requires a different ohm value. But as it’s on the negativ side i don’t know why the Tacho would be affected by that.

Did you remove the stock 280Z Electronic Ignition Module or at a minimum disconnect the Blue wire from the Module? The blue wire to the "-" post of the coil originates at the Electronic Ignition Module under the dash and supplies the "signal to fire" that has now been replaced with your 123 Module. The signal to the Tach tees off that wiring and goes through the 2.2 Ohm resistor before feeding the Tach. If the stock EIM is still wired in it could be interfering with the Tach signal. I've used many different ignition schemes and on a single coil ignition I've always been able to drive my tach properly with the stock blue wire no matter what EIM I used. But I completely removed the stock Ignition module under my dash first thing.

[PrincePaul]

7 hours ago, cgsheen1 said:

Did you remove the stock 280Z Electronic Ignition Module or at a minimum disconnect the Blue wire from the Module? The blue wire to the "-" post of the coil originates 

Yes that’s all gone. 
 

@Zed Head it gets power from the ignition position of the key pin 15 and if the coil produces sparks the minus of it closes the circuit for the relay. Kinda - something makes that relay special otherwise it would be a normal switch relay.

but I try this first next time. If that’s the problem than we’ve to figure out how to make that system work differently maybe with a optocoupler or so.

[PrincePaul]

Alright guys, thanks for your input.

it’s fixed now. The standard coil condenser which was on the plus side stock is now on the minus side of the coil to smoothen out the signal.

worked perfectly. Haven’t tried high rpm but signal is there so far.
 

just have to buy a new one so I don’t have to relay on the 40 year old one.

does someone know which Typ it is? Can’t find anything in the FSM. Maybe one of you knows how much farad it has?

 

Btw:

i also checked the other mentioned things:

resistor was 2.2k
the Stock coil as well as the new Bosch red have 1,3ohm

 

so everything is fine in that regard.

[DHA280Z]

Hi Paul Prince, could you post some pictures of the wring of the condenser? I have the same issue but I am keeping the original EFI system.

my tacho doesn’t work . 280Z - 1978

 

[PrincePaul]

45 minutes ago, DHA280Z said:

Hi Paul Prince, could you post some pictures of the wring of the condenser? I have the same issue but I am keeping the original EFI system.

my tacho doesn’t work . 280Z - 1978

 

Sure. Can’t find a better pick right now. It’s just one of those radio signal condensers which you also find on the alternator. Directly mounted on one of the coil bracket screws for ground and the cable connected to the minus side of the coil.

[DHA280Z]

I will try this fix.

may ias what you did with red&green block terminal wires, these used to connect to the distributor? The 123ignition distributor connects directly to the coil and ground, so far leaving these two wires unused. When I connected them to the +- in the coil, nothing happens. Should those be reconnected after the installation of the condenser? See figure

[PrincePaul]

Removed them completely, the transistor ignition unit where those come from is obsolete in my setup (123 with Weber Carbs)  So I removed all of its cables. But I´m not sure if some signals are needed for the ecu. Better check the FSM for the transistor ignition unit. It has its own chapter. The red and green wire are not needed for sure.

[DHA280Z]

Thank you for the hint. I will check the transistor wiring in the FSM.

great to be in the same time zone!!

[Zed Head]

The blue wire from the coil (-) terminal supplies the tachometer with the voltage signal.  You can leave it connected at the coil, but disconnected at the old igniton module.  It's on a branched circuit.

You can follow it out on the wiring diagram and see it.