Jump to content

IGNORED

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


Av8ferg

Recommended Posts

Posted (edited)

 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:  

 

image.jpg

 

Edited by Av8ferg
Link to comment
Share on other sites


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.

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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 .
  • Agree 1
Link to comment
Share on other sites

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.

  • Like 2
Link to comment
Share on other sites

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. 😁

  • Haha 3
Link to comment
Share on other sites

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?  

605057A0-7A36-4B52-9B18-00EAE14BBD70.jpeg

Link to comment
Share on other sites

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.

 

Link to comment
Share on other sites

Posted (edited)
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 by Captain Obvious
Link to comment
Share on other sites

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.  

Link to comment
Share on other sites

Posted (edited)

Start with the wiring diagram from the FSM:

image.png

It shows one wire coming from the fuse box: blue. There is another wire coming from the resistor: blue/white. The wiring diagram shows this as yellow/white. Finally there is a ground wire.

From this approach, the first thing to check is quality of the ground. Measure resistance to ground on connector on the dash harness side at the black wire. Also make sure there is no resistance from the connector on the gauge to the gauge body. Clean the connector with Caig Deoxit while you're at it.

Next, as I stated before, check the resistance from the blue/white (or yellow/white) wire at the dash connector to the negative post of the coil. You may need to make an extended lead with an alligator clip to reach. You can build your own probe with something like this: https://www.amazon.com/Insulated-Multimeter-Stackable-Connectors-Adapters/dp/B07C535GBD.

Also make sure the dash to engine harness connectors are clean.

 

 

Edited by SteveJ
  • Like 1
Link to comment
Share on other sites

Okay, I tested all those connection.  First us3 the continuity setting the the the resistance to verify the actual ohms.  
 

- Black wire on dash harness side to ground shows “short”. With a reading of 1.2 ohms,  

- Blue white (LW) on dash harness to neg post of coil.  Shows “open” with 2.23 k ohms

- Then tested Bluw White (LW) on diagram to the resistor and it  shows “short” with .3 ohms 

- other side of resistor to neg coil post shows “short” with . 3 ohms

-resistor itself tests ar 2.2 kOhms

-when I put a jumper where the resistor it goes I get a” short” reading with 1.6 ohms

This all looks correct to me.  

Of note the thee gauge lights to the tachometer do not illuminate with all the other lights on the dash.  New bulbs in there also.  

 

Link to comment
Share on other sites

Researching the web I found a post where a guy had the same problem after adding the ZX ignition.  ZedHead was on this post.  This guy had an MSD coil and when he went back to his OIC coil the problem went away.  I have the same coil I was using before I removed the ballast resistor?   Does anyone think adding a resistor to blue white on the coil would fix this.   Not sure if the old ballast resistor dropped the voltage to the tach.  Or I can try a different coil 
 

Here is another thread on hybrid Z.  This guy changed his coil too and it fixed the problem.   The stock coil is designed to be used with the ballast resistor and  is rated at 3 ohms without a ballast resistor you want a 1.5 ohm coil.    
 

https://forums.hybridz.org/topic/125373-tach-not-reading-below-~1200-rpms/

 

Link to comment
Share on other sites

I never had tach issues with ZX ignition in my 260Z. (Same general design as the 280Z tachometer circuit.) It was modified by a PO. I eventually bypassed the ballast resistor and using a coil with similar impedance as a 280ZX coil with an E12-80 module. No problems.

I'm not sure what you mean with respect to adding a resistor in addition to the one that's in the circuit. 

Link to comment
Share on other sites

Posted (edited)

Okay more research to run by you all.  The E12-80 ignition unit needs 12V to function as advertised. The e12-80 module likes a 0.84 to 1.02 ohm primary resistance coil because the currents and voltages match the modules' duty cycle.  So putting in a 3 Ohm coil could cause issues with E12-80 ignitions especially above 4500 RPM.   The 280Z tachometer uses voltage not current to read RPM.   It prefers 5-10v.  280z works great with a 1.0 ohm coil when there is a ballast resistor between it and the tachometer.  The ballast resistor only add the resistance after the engine is started.  If I want

let’s say 8v to the tachometer I need more resistance  between the coil (-) and the tachometer.  I’m thinking 8-10kohms.  This explain why when people put a higher primary resistance coil their tachometers began working properly. 
 

on CaliforniaDatsun’s website for a ZX distributor upgrade he has this blurb in the write up.

 

9F9F5DAF-709A-4B5F-87E3-86FF0D9F84E5.jpeg

Edited by Av8ferg
Link to comment
Share on other sites

The CA Datsun thing is probably for using a ZX distributor in a 240Z.

The 280ZX's use a resistor inline to the tach also, just like the 280Z's.  The 1978 ignition system is very similar to the ZX system.  Nissan just shrunk the electronics down.  1978 and 1982 both use a 0.84 - 1.02 coil primary circuit specification.  Both ignition modules are designed for the lower resistance primary circuit, and the tachometer system is also.  You could just copy the specs from the ZX system.  

1982

image.png

Link to comment
Share on other sites

The CA Datsun thing is probably for using a ZX distributor in a 240Z.
The 280ZX's use a resistor inline to the tach also, just like the 280Z's.  The 1978 ignition system is very similar to the ZX system.  Nissan just shrunk the electronics down.  1978 and 1982 both use a 0.84 - 1.02 coil primary circuit specification.  Both ignition modules are designed for the lower resistance primary circuit, and the tachometer system is also.  You could just copy the specs from the ZX system.  
1982
image.thumb.png.faad068e9afb3e4c7667c95efb6bda06.png

I’ve pretty much done that already.
Link to comment
Share on other sites

34 minutes ago, Av8ferg said:


I’ve pretty much done that already.

Couldn't tell, I looked back but I don't think you mentioned which coil you were using.  Maybe in your other thread.

8 hours ago, Av8ferg said:

 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.  

I had a vague memory of a similar thread (among many, tach problems are common) and found it.  Post #29 is the one.

 

  • Like 1
Link to comment
Share on other sites

I had a vague memory of a similar thread (among many, tach problems are common) and found it.  Post #29 is the one.
 

Okay, you’ve convinced me to try this. I have another completely rebuild ZX distributor that I’ll try out. I wanted to test it anyway so I’ll see what happens. I may even have an additional E12-80 ignition unit on top of that .
Link to comment
Share on other sites

Posted (edited)

Well, I have figured this out and now and can post this for future Z owners that convert their 280Z to a ZX (E12-80) ignition.  
 

First I tried what ZedHead recommended and replaced the (E12-80) with on of my OEM backups.  Result.. no change tac remained non functional below 1200 RPM.  
 

I’ve kept coming back to my original theory which was the Tac doesn’t like voltage greater than about 12.5V.  I surmised this because I put my multimeter in the tac and measured the voltage charges as I revved the engine.  Voltage drops at the tachometer at higher RPM.  I noticed that around 12.3v it would begin to indicate RPM.   
I then checked my primary resistance on the coil.  It came to .6 Ohms   Using Ohms laws voltage = current x resistance.  I determined that with a .6 ohm coil I was pushing the max alternator voltage to the tachometer.   
So I went out and bought a 1.5 Ohm coil.  Put that one it and the tac magically worked.   I have three coils on hand now and tested each one.  
 

With the 1.5 ohm coil installed I should be reading a lower voltage at the tach   At idle it’s around 10.3 v. 
With the 1.0 ohm coil installed I read around 12.5v at the tach and the RPM worked at idle

With the 0.6 ohm coil installed I read 13.4v at the Tach and no reading at idle.  
 

So I believe the mystery is solved.  I learned a lot on this problem and I also got to test my backup ECU and (E12-80) ignition modules.  
 

Time to move on the the next problem….do they ever end?    Thanks for the help guys! 

Edited by Av8ferg
  • Like 4
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.