240z distibutor upgrade and tach from 280z wiring question

[KoolMan]

I have done the E12-80 Distributor upgrade withe the MSD Blaster 2 my z has been running great after the upgrade.
Since the upgrade I have been running my z without the tach it hasn't worked since I did the upgrade.

Anyway I'm trying to figure out how the wiring goes. I have been reading up on it but I think my problem is that I don't remember which wires are the ones that go to the resistor(removed after upgrade) I uploaded a picture of my setup.

I have a Connected the E12-80 to the coil and found the current wire and connected it since I did not have the tach I did not do anything else with the rest of the wires. I have four wires 3 are not connected right now.


A) Was connected to the coil with the points distributor. Green/White and the other is black with yellow tip thicker cable
B ) Was connected to the resistor. the cable one is black/yellow and the other is black.
C) Added for the E12-80 distributor

The only way that I can get the Z to start is to connect the (pic B ) black wire to the coil all others don't work.


I have a four cable tach on my z and just got a 280z tach that ill be putting in. But I still have a question about this.
On the tach I moved everything to the other 240z housing but I still dont understand what I'm suppose to do with the white/loop cable that has the black and read tape on each side. I know that the black wire moved from the top (240z tach) to the bottom (280z tach)

Thanks in advance

[beermanpete]

The 4 wire tach (240Z tach) uses a current sensing circuit on the positive side of the coil. With the original points type distributor the +12V (black wire) connected to the ballast resistor. The green/white wire runs from the other side of the ballast resistor to the tach. The black/white wire returns from the tach to the positive side of the coil.

To get the tach to work you need to connect the solid black wire to the green/white wire (remove the black wire from the coil) and connect the black.white wire to the coil.

It is possible that the E12-80 system will not provide the 4-wire tach with the correct current pulse wave-form to get a reading from the tach. In this case you will need to use the 3-wire (280Z tach). The 280Z tach gets it s signal from the negative side of the coil so you will need to re-configure the wiring appropriately to make it work.

[KoolMan]

The 4 wire tach (240Z tach) uses a current sensing circuit on the positive side of the coil. With the original points type distributor the +12V (black wire) connected to the ballast resistor. The green/white wire runs from the other side of the ballast resistor to the tach. The black/white wire returns from the tach to the positive side of the coil.

To get the tach to work you need to connect the solid black wire to the green/white wire (remove the black wire from the coil) and connect the black.white wire to the coil.

It is possible that the E12-80 system will not provide the 4-wire tach with the correct current pulse wave-form to get a reading from the tach. In this case you will need to use the 3-wire (280Z tach). The 280Z tach gets it s signal from the negative side of the coil so you will need to re-configure the wiring appropriately to make it work.

so I connect cables in B and connect the black cable in the A box to the negative side. right?

and on the tach I connect the negative side of the coil to the post on the back of the tach were the loop would be right?

I changed the housing from the 240z to the 280z so the cables on the right of the tach were changed the black one is now on the bottom 280z. were before it use to be on the top. is this correct?

Thanks again

[beermanpete]

so I connect cables in B and connect the black cable in the A box to the negative side. right?

and on the tach I connect the negative side of the coil to the post on the back of the tach were the loop would be right?

I changed the housing from the 240z to the 280z so the cables on the right of the tach were changed the black one is now on the bottom 280z. were before it use to be on the top. is this correct?

Thanks again

If you are using the 280Z tach you need to connect a wire from the negative side of the coil to the ignition input on the tach. I do not know the wire colors on the 280Z tach, nor do I know how you modified the wiring when you installed it so I cannot say which color wire to connect to what. Since your car is running simply run a new wire from the negative terminal (on the coil) into the car to the tach.

If you want to use the existing wires the black/yellow is the likely candidate. Make sure that it does not have power in it under ANY condition (key off, key on, while cranking).

[KoolMan]

ok so right now i have the car running with the old tach and its all bouncy. i was told the upgrade would sort of fix it or make it less since the distributor is a electronic from the zx. I do have the L28 and the current 240z tach does not read the rpm's that well since it was designed for the L24.

so i can just leave it as i currently have it and just run another cable from the neg (-) side of the coil to the terminal on the tach.

Thanks


Edit:

Thanks
I got it working.
all I need to do is run a cable back to the dash and im all set.

thanks again for replaying.
out of 4 different post on 4 different sites this is the only one i got a reply back.

[beermanpete]

Good to hear you got it to work. The tach in my 240Z is bouncy as well. It seems to be typical. There is no reason the tach will need to be different due to using the L28. What is important is the ignition system. The 240Z tach is designed for points and does not work well with some of the electronic ignition systems available.

[Blue]

I am wondering if an extra wrap of a coil or two at the inductive tap on the back of a 240z tach will make it work with the ZX distributor?

[KoolMan]

I'll give it an extra loop this weekend and I'll report back

thanks

[Blue]

For completeness, I did this 2nd wrap too and no change. The early 240z distributor will not work without modification.

[ZAutobahn]

The original 240-Z tachometer will work just fine with the 280ZX electronic ignition and a high performance coil IF you don't bypass the Ballast Resistor. The original 240-Z ignition uses a Ballast Resistor to reduce the voltage from 12V down to about 8 or 9V in order to protect the points from burning. Note that when the key is twisted to the Start position the Ballast Resistor is bypassed in order to provide the full 12V to the Coil and Points. But as soon as the key is released the circuit is directed through the voltage reducing (performance robbing) Ballast Resistor. The 240-Z tachometer uses an inductive loop to sense voltage changes on the positive side of the circuit - but it is designed to work properly with the reduced voltage provided by the Ballast Resistor. It can't handle the full 12V it receives if the Ballast Resistor is eliminated from the circuit (and the "bouncing needle" on the tachometer is the result).

The 280-Z tachometer on the other hand is of the more common design that senses pulses on the negative side of the circuit and it functions just fine at the 12 volt level. So if one wants a 240-Z to function at the higher level of ignition efficiency provided by bypassing the Ballast Resister in order to provide the full 12 Volts to the Coil AND have a functioning tachometer, they must retrofit a 280-Z or an aftermarket tachometer.

I converted my 240-Z (L28) engine to the ZX Distributor / High Performance Coil setup 14 years ago. When I did it I bypassed the Ballast Resistor and of course got the "Bouncing Tach Syndrome". So I wired the Ballast Resistor back into the system and my Tach's schizophrenia disappeared. I decided I prefered having a stable Tach even if it meant a slight performance hit while I waited for the day I got up the wherewithal to buy and install a 280-Z Tach. Fourteen years later and here I am still procrastinating... :-)

[malibud]

I dont want to high-jack but my problem is quite similar. I to upgraded with an l28 and electronic ign. All was working good (tach with ballast resistor) until ... I left the key in the ignition over night. Woke up to dead battery. When i got it running now my tach goes to redline bottom when key is on and back to 0 when off. tried a new ballast resistor a nothing any suggestion ?
thanks

[beermanpete]

I dont want to high-jack but my problem is quite similar. I to upgraded with an l28 and electronic ign. All was working good (tach with ballast resistor) until ... I left the key in the ignition over night. Woke up to dead battery. When i got it running now my tach goes to redline bottom when key is on and back to 0 when off. tried a new ballast resistor a nothing any suggestion ?
thanks

The tach is bad.

[malibud]

That's what I thought thanks might be time to upgrade . If I go to a 3 wire I just connect the the 2 white wires together right?

[beermanpete]

That's what I thought thanks might be time to upgrade . If I go to a 3 wire I just connect the the 2 white wires together right?

Correct.

[3ryce]

What year and month was your z made.? Mine was 6/73 and it was the three wire tach style. Had me confused for the longest time. There is a thread on here on what I did as well and a thread about swaping the tach too.