280zx distributor upgrade in 280z, tach now doesn't work

[Ownallday]

Hello, I just recently ditched the Stock FI system on my 1978 Datsun 280z and went over to Triple Weber's, with it I also upgraded to the 280zx distributor with the E12-80 ignition and upgraded the coil to the MSD Blaster Coil 2. Car started up like a dream considering they are brand new Weber's and haven't been tuned. However my Tachometer stopped working properly. Either it doesn't work  or it somewhat jumps around sporadically while driving. Am I missing something?

[SteveJ]

Have you verified the resistor in the tachometer circuit is good? Do you have a meter like this to test the signal?

[Ownallday]

14 minutes ago, SteveJ said:

Have you verified the resistor in the tachometer circuit is good? Do you have a meter like this to test the signal?

Is the resistor somewhere along the passenger side? I can test it tomorrow but the tach was working perfectly before

[SteveJ]

Many people have performed the ZX distributor swap into 260Zs and 280Zs and maintained tach functionality. Did you unplug the TIU?

The resistor is most likely on the passenger side. It is on my 260Z, but I can't say for sure on a 78. 

[siteunseen]

I followed @240260280 tech tips on my '77 and it worked like a charm.

 

https://www.atlanticz.ca/zclub/techtips/distributor/index.html

 

[Ownallday]

3 minutes ago, SteveJ said:

Many people have performed the ZX distributor swap into 260Zs and 280Zs and maintained tach functionality. Did you unplug the TIU?

The resistor is most likely on the passenger side. It is on my 260Z, but I can't say for sure on a 78. 

This is why I am confused why mine stopped working. I did not mess with the TIU, as a matter of fact I had to look it up just to see what it was

 

3 minutes ago, siteunseen said:

I followed @240260280 tech tips on my '77 and it worked like a charm.

 

https://www.atlanticz.ca/zclub/techtips/distributor/index.html

 

When installing the ZX dizzy I followed this exact guide. Only difference is the 1978 280z does not have a ballast resistor

[Zed Head]

Just had a similar problem in a separate thread.  Maybe there's a batch of bad ZX modules out there.  The 78 ignition module is about identical to the ZX module design.  Current limiting, etc.  The tach shouldn't see a difference.

 

[Ownallday]

20 minutes ago, Zed Head said:

Just had a similar problem in a separate thread.  Maybe there's a batch of bad ZX modules out there.  The 78 ignition module is about identical to the ZX module design.  Current limiting, etc.  The tach shouldn't see a difference.

 

So replacing the Ignition module solves the problem? I can't see the issue being anything else since the tach was working perfect before this switch. I believe my issue is similar where my tach only works over a certain rpms.

[Zed Head]

1 hour ago, Ownallday said:

my 1978 Datsun 280z  

with it I also upgraded to the 280zx distributor with the E12-80 ignition 

The 78 ignition module had the same functionality as the ZX ignition module.  So your swap was not really an upgrade, it was just a swap, assuming that both worked as they were supposed to.

heyitsrama's thread kind of speaks for itself I think.  I've never used a ZX distributor myself.  But the aftermarket ZX modules are known to be of questionable quality.  People get bad ones new.  You can find posts about them around the internet.

[Ownallday]

3 minutes ago, Zed Head said:

The 78 ignition module had the same functionality as the ZX ignition module.  So your swap was not really an upgrade, it was just a swap, assuming that both worked as they were supposed to.

heyitsrama's thread kind of speaks for itself I think.  I've never used a ZX distributor myself.  But the aftermarket ZX modules are known to be of questionable quality.  People get bad ones new.  You can find posts about them around the internet.

Ouch, here I was under the impression that I was upgrading since I know the ZX distributors are a popular upgrade to those swapping over to Triple Weber's like I just did. So basically I should swap back over to the stock 280z Distributor and pray my tach works or I can replace the ICM and hope I get one that isn't bad quality. I'll do some researching.

[EuroDat]

2 hours ago, Ownallday said:

This is why I am confused why mine stopped working. I did not mess with the TIU, as a matter of fact I had to look it up just to see what it was

 

When installing the ZX dizzy I followed this exact guide. Only difference is the 1978 280z does not have a ballast resistor

The 280ZX dizzy has the TIU fitted on the side of the distributor which is btw not a good spot for it. All the 280Z models had an external TIU located in the passender sideof the cabin, near the fuse box. You have the 78 which has a simple 6-pin connector. 

When you install the 280ZX distributor you must disconect the old TIU. You need to disconnect the 6-pin plug.

Is blue wire connected to the coil negative? The blue wire was the trigger from the TIU for the coil, but now it only communicates through a resistor to the tacho.

If your engine is running properly and the tacho was working before the swap, then it is probably one of these two things. Not likely to be the resistor, but you should still check it if it is open circuited.

A dodgy Matchbox TIU will work the tacho, but it will generally be erratic and bouncy. It oftens drops to zero and jumps back up again and all over the place, but it will generally do something.

[Ownallday]

On 12/5/2020 at 12:23 AM, EuroDat said:

The 280ZX dizzy has the TIU fitted on the side of the distributor which is btw not a good spot for it. All the 280Z models had an external TIU located in the passender sideof the cabin, near the fuse box. You have the 78 which has a simple 6-pin connector. 

When you install the 280ZX distributor you must disconect the old TIU. You need to disconnect the 6-pin plug.

Is blue wire connected to the coil negative? The blue wire was the trigger from the TIU for the coil, but now it only communicates through a resistor to the tacho.

If your engine is running properly and the tacho was working before the swap, then it is probably one of these two things. Not likely to be the resistor, but you should still check it if it is open circuited.

A dodgy Matchbox TIU will work the tacho, but it will generally be erratic and bouncy. It oftens drops to zero and jumps back up again and all over the place, but it will generally do something.

Okay so I traced out this TIU and found this

 

Going to assume this is the TIU as it had six pins on it. I disconnected it, went for a drive and same results. I can confirm that with this box plugged in or unplugged my rpms only work above 2000rpms. Anything below that my Tach is dead.

The blue wire is hooked up to the negative terminal on the MSD coil.