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tacho says no. 280zx


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Hi, 280zx factory tacho, rb20det engine/ecu

 

i was running an afermarket tacho directly in front of the factory one, but it was pretty disorientating switching between it and the speedo, as they werent on the same plane. so i wanted to go back to a factory tacho.

 

i've just plumbed the line into the factory tach feed wire, but no luck. what am i doing wrong?

 

currently the line is pin 7 (tach feed) from the ecu, spliced with a 12v wire from some other place, and a 10k resistor, as this was the setup i needed for my aftermarket tach

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did a search but didnt turn up much unfortunately. one person saying they hadnt heard of a 280zx tacho working with an rb20det, another person saying it should run as-is. the 10k resistor method i found on r31.com (australian skyline site) and that worked fine for the aftermarket tacho that i was previously using.

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  • 4 months later...

did a search but didnt turn up much unfortunately. one person saying they hadnt heard of a 280zx tacho working with an rb20det, another person saying it should run as-is. the 10k resistor method i found on r31.com (australian skyline site) and that worked fine for the aftermarket tacho that i was previously using.

 

So still no news on the 280z Tacho with an RB engine???

 

Feel free - it doesn't have to be an RB20 - any info on this topic would be very helpful.

 

There are lots of posts about using a stock tacho but none, in my view, that deal with the subject fully.

 

If someone has the info then I don't mind writing it up for the community?

 

Oh yes and for you sarcastic lot (you know who you are) - p-lease, I have read all posts on this topic that the search engine throws up.

 

Anyone with anything constructive?

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this is what I used with a autometer Gauge. I don't know if it will work but it's worth a try

 

RB20_Tacho_Wiring.jpg

 

I know my 280Z tach doesn't work with my R34 RB25. I will be putting a scope on it soon to figure out why. I'll post when I figure it out.

 

Pete

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I know my 280Z tach doesn't work with my R34 RB25. I will be putting a scope on it soon to figure out why. I'll post when I figure it out.

 

Pete

 

Pete, What year tach? The '78 is a different beast. I haven't had much luck with those without an adapter.

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Please can you explain how the 78 280z tacho is different to other years?

 

Nope, sure can't. All I can tell you is I've tried several with HEI's and aftermarket EFI's, with no luck. I haven't been able to get one to respond. BRAAP has run into the same thing. They can be *made* to work, but I've never been able to get one working without resorting to trickery.

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Nope, sure can't. All I can tell you is I've tried several with HEI's and aftermarket EFI's, with no luck. I haven't been able to get one to respond. BRAAP has run into the same thing. They can be *made* to work, but I've never been able to get one working without resorting to trickery.

 

I have tried two of them, and I guess I might be lucky (un) that they are both 78'. Doesn't the 78 have the same ignition module as all 280Zs? Does the 78' have an external resistor like other 280Zs? If not, it could explain it. Anyway, when I get an exhaust on my RB I will hook up the scope and spend some time looking at it.

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I have a wiring diagram for a 280z that I have attached - I hope it works as this is my first attachment under the new system.

 

The tacho wire (LW) seems to go through a resistor to a wire (L) which links to both the coil and the transistor ignition unit and which also seems to carry on to connect to pin B1 of the ECU.

 

Regards

78-280Z_wiring.pdf

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  • 1 year later...

Post #75

http://forums.hybridz.org/index.php/topic/72003-260z-rb25det-s2-motor-badazz-260zr-and-some-s/page__st__60

 

Im pretty sure the "Pull Up" resistor will work with the 280ZX tach. It seems to be a matter of finding the correct resistance to pull the voltage up enough to trigger the tach. If you get no other answers that is what I would try to do. Get an assortment of resistors and try them.

 

Not sure what the deal is with the 78 280Z tachs in this thread.

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I have been told (but haven't tried it myself) that on the back of a 280ZX tach there is a white resistor, if you remove this the tach should work straight off an RB computer, this may also work for aftermarket ECUs.

Edited by djz
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  • 2 years later...

Was anybody able to figure this out at all?

 

Im trying to wire in an rb26  tacho out signal to my 280zx..

 

I can see that the 78 280z tacho wiring is the same as the 280zx.. The tachos both connect to the NEGative pole on the ignition coil.

 

The question i guess is how is the earth to the ignition coil (blue wire) broken? Does it break via a cam in the distributor? Or does the ECU itself break the earth? The ECU could break earth if it has a CAS I guess, but I dont think NA 280zx's and the 78 280z have a CAS.

I can't actually tell following wiring diagrams since they all show wiring up to the power transistor / ic unit, but then dont have any more specific details on the internal IC / Distributor wiring.
 

I was thinking that if you were to take apart a relay and remove the switch and kept the coil, you could run a constant 12v through the coil and connect it to earth and the tacho..

You could then use the ecu tacho out to somehow break the earth? I've heard that the tacho supposedly provides a -5v square wave.. Could you use a transistor / mosfet / jfet to switch the relay coil earth on and off to replicate the original ignition system?

Edited by moodah
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