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

[Av8ferg]

 I’ve been troubleshooting and searching online to figure out my tachometer problems since I installed the ZX distributor with the E12-80 ignition module.   My problem is I don’t get any tac readings below 1200 rpm.   
Doing my research I’ve seen many other with this problem but the links have died on some of these posts so I’m only getting one page of most of these threads.  
So today I bought a new condenser and connected it to the negative side of the coil, because my old one broke.  I’m not sure what the uF rating is but is didn’t help the problem.  The stock ignition module on passenger side is completely disconnected.  I pulled the tach resistor off the harness located in the passenger footwell area and the connected it to the red wire on the back of the tac.  When I did this the tac stopped working completely.  I put the resistor back in it normal location and the tac worked but still didn’t show rpm below 1200.  
What I’ve read is that is the the tac needs a voltage between 5v and 10v.  Outside that range is when problems arise.

Not sure where to go from here but I know someone on here has done this ignition mod and figured this out.  Any help is appreciated!  Also I’ve tested two separate tachometers and both have the exact same Indications. 
Video link:  

 

 

Edited May 20, 2022 by Av8ferg

[Zed Head]

It did work when the engine was cranking, but stopped when the engine started.  Might be a clue for the guys that know electronics.  While cranking the overall system voltage will be lower.  As soon as it starts you get alternator voltage.

Do you have any spare E12-80 modules?  Maybe the problem is there.  Might be worth a swap, just to confirm.  At low RPM the module will be "working harder" to limit current for "dwell control".  I don't really understand the details of current-limiting but that's how the ZX and GM HEI modules work to get maximum coil charge without overheating the circuitry.

And, of course, don't overlook the grounds.  The module grounds through the distributor body and the distributor body grounds through a separate wire or the mounting pedestal.

[siteunseen]

I followed this to put an E12-80 in my '77 then again on my '72. The wiring diagrams are different though for a 240. They are at the bottom of the page.

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

Edited May 20, 2022 by siteunseen

[SteveJ]

First, the condenser should be on the positive side of the coil. Do you still have the ballast resistor in the circuit, or have you jumpered that out?

Next, measure the resistance from the negative post of the coil to the tachometer connector blue wire. It should be around 2.2k Ohms or so.

Also, is the TIU disconnected? Is the blue wire at the TIU interface taped off so it cannot come into contact with anything?

[Zed Head]

The "condenser on the negative post" might have come from a solution I developed in the past for a tachometer problem, and have recommended for the occasional odd tach problem, as a last resort.  In my case, the needle would just sit and quiver until the condenser/capacitor was attached.  My general theory was that it absorbed voltage spikes/noise that were causing the tachometer problems.  Basically it cleaned up the voltage signal.  Whatever the reason, it worked.  I even confirmed it later when the wire broke off of the condenser and the tach quit working.  That was with a GM HEI module though.

[Av8ferg]

First, the condenser should be on the positive side of the coil. Do you still have the ballast resistor in the circuit, or have you jumpered that out?
Next, measure the resistance from the negative post of the coil to the tachometer connector blue wire. It should be around 2.2k Ohms or so.
Also, is the TIU disconnected? Is the blue wire at the TIU interface taped off so it cannot come into contact with anything?

First, the condenser should be on the positive side of the coil. Do you still have the ballast resistor in the circuit, or have you jumpered that out?
Next, measure the resistance from the negative post of the coil to the tachometer connector blue wire. It should be around 2.2k Ohms or so.
Also, is the TIU disconnected? Is the blue wire at the TIU interface taped off so it cannot come into contact with anything?

Steve, thanks. Word on the street was you were the guy with exceptional knowledge in this area. I won’t get to the car this weekend but I’ll go and confirm everything you mentioned. I thought I totally disconnected the TIU but I could be wrong . I may have reconnected it because I thought the wires were just hanging there. I’ll move that condenser over too the positive side and report back my findings .

[Av8ferg]

ZH, I saw that post where you talked about putting on the negative side of the coil. I’ve seen it on other posts as well like over on HybridZ. Was hoping it would work for me. I’m going to follow SteveJ and see where it leads me.

[SteveJ]

18 hours ago, Av8ferg said:

 

Steve, thanks. Word on the street was you were the guy with exceptional knowledge in this area. I won’t get to the car this weekend but I’ll go and confirm everything you mentioned. I thought I totally disconnected the TIU but I could be wrong . I may have reconnected it because I thought the wires were just hanging there. I’ll move that condenser over too the positive side and report back my findings .

 

I guess you'll find out how much is true and how much is stuff I made up. 😁

[Av8ferg]

Well it can’t be any worse than my complete lack of knowledge in this area.  The fact that when I removed the stock 2.2k ohm resistor from the harness in the passenger foot well and that caused the tachometer to not work at all make me think I could have the TiU still connected.   And what the purpose of the capacitor on the post terminal, I know it for noise canceling but how does this effect the tachometer, or is this bad info?  

[SteveJ]

Typically the condenser suppresses noise with the rapid changes in the magnetic field of the coil. Interestingly enough, the 260Z does not have a condenser in the wiring diagram for the ignition. I'm not sure why.

The 1980 has the condenser on the positive side of the coil (E12-80 ignition module).

My thought is that if the resistance is too high between the ignition module and tachometer, your tachometer isn't getting the signal it needs to react. Also, if the blue wire for the TIU is coming into contact with another wire (or is connected to the TIU still), that could affect the signal quality going to the tachometer. We know the blue wire for the TIU isn't solidly grounded, otherwise your car wouldn't start/run.

A few years ago, a friend brought over a customer's 260Z that wasn't running that well after a ZX distributor swap. I don't recall if he said whether or not there were tach issues. The first question I asked was, "Did you disconnect the TIU?" After a Homer Simpson "D'OH!" he disconnected the TIU, and all was good.

You may consider adding a meter like this to your arsenal: https://www.amazon.com/gp/product/B0002LZU7K

Among other features, it has a tachometer. That can make for better troubleshooting and analysis, not only for this problem, but for tuning issues, too.

 

[Captain Obvious]

2 hours ago, Av8ferg said:

The fact that when I removed the stock 2.2k ohm resistor from the harness in the passenger foot well and that caused the tachometer to not work at all make me think I could have the TiU still connected. 

When you remove that resistor from the harness, you completely separate the tach from the ignition circuit.

With that resistor out, the RPM input signal to the tach is open circuited. That's why the tach didn't work at all when you pulled that resistor. 

That said though... It really is important that the original ignition module be disconnected, so double check just to be sure.

Edited May 22, 2022 by Captain Obvious

[Av8ferg]

Okay, was gone all weekend for kids sports tournaments but I’m back in the garage this AM.   I’ve moved  the capacitor (condenser) to the positive terminal on the coil.  Stated the car…no change in the tachometer readings.   Then I completely removed the TIU in the passenger footwell and wrapped covered and wrapped this wires that went to that.  Started the car….no change in the tachometer.    I then put my voltmeter on the red wire going to the back of the tachometer and started the car.   13.3 V at idle and 12.8 V while reviving the engine.   I read that t tac needs a lower voltage here, but when I removed the inline resistor in the passenger foot well ( and left that circuit open). Then built a jumper to put the resistor on the red wire reconnecting to the back of the ta, it didn’t show any RPM at all.  Thought I maybe needed to jump the wire to close that circuit where the resistor originally came but wasn’t sure if that would make a difference.  SteveJ….any other ideas?  I haven’t changed out the E12-80 unit for one of my backups but I really didn’t think that would make a difference.  Any ideas appreciated.