TACH acting very funny

[Arne]

A resistor is recommended with the Pertronix for 1.5Ω coils, not needed with 3.0Ω coils. That said, I'm betting there are plenty of cars out there running Pertronix with 1.5Ω coils and the resistor bypassed.

[kully 560]

WHen I first joined this forum, I noticed my tach was never really happy anywhere above 5k. I quickly determined that it was in fact the tach that was not happy, rather than the engine.

Today, it was the first really hot day out, and after being in the sun all day and then getting stuck in traffic, I noticed my tack was hovering around 4k. Which in itself is not that unusual, but I was idling at a stop light. I noticed it then began to bounce slowly back and forth as it made it way to peg the needle past 8k. Now since I was at idle, I was pretty sure that this was not really happening :stupid:. The car ran just fine, so I was really not worried, figured the tach was just borked.

Now when I got it home I turned off the key and it immediately flopped back to zero. Flopped is pretty much the right word. When I turned the key back on, but did not start the engine, it slowly rose to peg the tach again. I went inside to mill it over.

I went back outside in the garage after grabbing some water and fired her up again, about 10 minutes had passed. The tach was working.

Ahhhhh Haaaaaa the plot thickens!

I think this has the signs of a tach thats on its last legs. THe thing is though when it operates its dead smooth and pretty accurate. Well up to about the 5500 rpm area anyway.

So, my question, is, could this be just a bad connection somewhere, or is the fact that the heat may have caused this just a sign that the tachs internal electronics are just too old and somewhere the Ohm (ie resistance) load is way to high. Or it could be short...So...........

I am going to start by cleaning off the terminal ends around the coil and resistor on the firewall. Then I will look for any frayed wiring.

I have an extra tach in the box I can replace it with, but the thought of pulling my tach back through my full dash cap is less than exciting...

THanks for any answers..

my 1974 260z had been jumping around also with turn signals on some times lights etc this was after the 79 dissy upgrade .so I used the msd tach adaptor and no luck . spoke to the tech at msd and he recommended to use a relay and feed the tack directly from battery bingo my tach is dead calm works perfect . might be worth a try to feed it from the battery direct and see if it might be something else causeing the problem kurt

[moritz55]

Zedyone Kenobi - this past weekend I swapped out my flakey '73 tach with another 240z stock tach. The replacement appears to work nicely - however it's old and can break anytime as well.

Question for folks following this posting.

1) Is there anyone on this site that will repiar a Stock Tach ?

New Tach Installation for 240z ...

I do have a 240z Tach with all New Electronics added to enable a (-) Coil Trigger off of new electronic ignition. I'm trying to figure out to to integrate Negative Trigger (New Tach) it into my Mallory Unilite Dizzy, Mallory Promaster Coil & MSD 6A box. To get my stock tach to work I added the MSD Tach adapter with the ballast resistor.

(see the 1st page of the attachment)

Question:

2) How would I integrate the NEW (-)Negative Trigger Coil Tach into my current set. Any help is appreciated.

MSD 6A Wiring 05-13-08 Layout.doc

[Arne]

1) Is there anyone on this site that will repiar a Stock Tach ?

A former regular here (EScanlon) had discussed this possibility a couple of years back with a friend who is/was some sort of electrical/electronic engineer. The initial thought was that the 240Z tach is a very simple device, and it should not be hard to repair one. There was talk of dissecting a bad one for testing, which I happily donated to the cause. No results were ever reported, so I don't know what became of this project.

[ChrisZ]

Mark M, do you have a 3 or 4 wire tach ?

Chris

[moritz55]

I have the typical 4 wire connector. One Orange wire, One Black wire, and a white wire loop w/Red tape & w/Black Tape into the same connector. The white wire is an inductive loop that completes the ignition circuit.

Here is a photo attached:

Many thanks..

Edited June 29, 2009 by moritz55

[ChrisZ]

And you know it is triggered from the positive side as standard!

If you want it triggered fron the negative side, then get a 3 wire.

Chris