240z (280z block) - rev counter not working - troubleshooting tips?

Graeme - CZ

Graeme - CZ

Club Member
Hi all,

The rev counter on my 240z has never worked. Before I start trying to diagnose this, I am sure someone can probably advise me. Car has a 280z 5 speed block in it. My first question is that has the engine change rendered the rev counter unworkable in it's current state? I don't know whether it is mechanical or electronic?

Is there an easy fix or things to check out?

Regards, Graeme
 
Take the dizzy cap off and u can see whether there are points or not. As it’s a later engine it will most likely have an electronic dizzy with no points. There are other threads on here on how to reconnect the wiring to get your tach working, that’s if you still have all the original wiring in place, which I didn’t
 
Yeah, it's an electronic distributor I have. No idea about wiring though. Any tips on threads worth checking out?
 
Have a look at this site which is where I got the wiring diagram from.

http://atlanticz.ca/zclub/techtips/distributor/index.html

If you have the electronic dizzy with a black module with 2 terminals, this should do it. There are 2 wires that need joining together to get the tach working. This can be done near the coil or at the ignition switch end. You no longer need the ballast resistor but you do need to swap your coil to a 1.5 Ohm coil otherwise it will not run very well and your coil may overheat & fail - been there & done it!!
 
In a lot of cases with the rev counter not working and the dizzy and coil has been changed and the ballast resistor has been removed people tend to take the power lead to the ballast and put it directly to the + side of the coil. Doing this stops current going to the rev counter. the outlet side of the ballast the wire goes all the way through the loom and on to the rear of the rev counter where it forms a small loop through a plastic block then goes all the way out to the + side of the coil. When the coil fires it creates a pulse that goes through the coil + wire so the rev counter counts these pulses, so if your wiring has left out the ballast cable you may have a spare wire by your coil. All you need to do is take the coil + wire and connect it to the loose cable so the rev counter is back in the loop and the rev counter should work.
Adrian
 
51BB506E-A486-44E0-B5C6-E5E315DAA0A2.jpeg Apologies for the thread hijack but I’ve had the same issue with my L28. Based on the comments above, Adrian, would you suggest I connect the cut short spare wire (green in the centre of the picture above the right hand side ht lead) in the pic to the positive connection on the coil?

What is the best best way to check it first?
Can I do any damage?

Sorry for the stupid questions, I’m still learning sharply since entering Z ownership!
 
As Adrian240z said the 12v feed to the coil goes via the tach ( inductive loop)
There should be two black and white wires near the coil this is the wire that loops the tac
Also a green and white wire 12v feed I expect this has been connected direct to the coil?
Take it off the coil and connect to one of the black and white wires the other black and white then goes to the coil
 
I'm doing similar with my tach now. I only seem to have one black and white wire though. I've got blue, green and white, one black and white and a red!
 
I dont seem to have the block that you have @jonbills

This is what mine looks like:

Blue/Black goes to the dizzy from the coil

White/Black goes from the loom to the coil
Blue goes from the loom to the same terminal on the coil as white/black

Ive got a green and white spare from the original loom

Then a spare red also going to the dizzy, I guess its been electronic ignition before

20220827_181300.jpg20220827_181328.jpg20220827_181349.jpg20220827_181359.jpg20220827_150814.jpg
 
s2k_adz said:
I'm doing similar with my tach now. I only seem to have one black and white wire though. I've got blue, green and white, one black and white and a red!
Click to expand...
I’d say your 260z doesn’t have a inductive loop tach. Later cars have tach as in photo
I’d open up the loom around the coil to see what colour wires you have and if any have been taped up.
Really need to see a photo of the wires to coil/ ballest on a 260z
(tach seems to have a Green wire ,Black wire ,Red/Black)
 

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Fairlineguy said:
I’d say your 260z doesn’t have a inductive loop tach. Later cars have tach as in photo
I’d open up the loom around the coil to see what colour wires you have and if any have been taped up.
Really need to see a photo of the wires to coil/ ballest on a 260z
(tach seems to have a Green wire ,Black wire ,Red/Black)
Click to expand...
Thanks Neil! I'll pull the tach out later if I get time and take a photo of the loom.

When you crank the car, the tach works. As soon as the engine kicks in it dies again.

I don't have the metal block they all join too like in Jons picture.
 
s2k_adz said:
Thanks Neil! I'll pull the tach out later if I get time and take a photo of the loom.

When you crank the car, the tach works. As soon as the engine kicks in it dies again.

I don't have the metal block they all join too like in Jons picture.
Click to expand...
No you just have a 12v non ballest coil to get the car started .Think you lost the ballest resistor if I recall?
 
Fairlineguy said:
No you just have a 12v non ballest coil to get the car started .Think you lost the ballest resistor if I recall?
Click to expand...

I cant remember but that wouldn't suprise me Neil - That could be whats buggering it up then? Ill getn on the hunt for one - Does that mean changing the coil too?
 
So I've had a mess about today and pulled the rev counter out. Its getting power when the ignition is on but it doesn't seem to be getting any current down the green and white wire. I continuity checked this and it seems as though its run to earth somewhere as I seem to get continuity anywhere on the car that isn't insulated which is odd! I might try running a wire direct from the coil to the rev counter but would it need a resistor in between?
 
This is the back of my tach so I think you're right. I'll keep playing about with it I think I'm going to run a wire straight from the coil to the tach. Would this do any harm?IMG-20220913-WA0015.jpg
 
Below copied from an old post by Mr. F.

"Coil +ve - black with white stripe - test for 12V positive. Returns from tachometer loop. Drops to 9V as resistor warms up.
Coil -ve - black with blue stripe (or blue on 240Z?) - this lead goes direct to connection on side of distributor.
Resistor - blue 12V positive in; Green with white stripe out to tachometer loop.
For points distributor only. Assumes all original wiring is intact!"

I would check that the wires follow the logic above, especially the ones which say tachometer loop, take photos of how they are so you can reverse them and put them back if it doesnt work.
 
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