Nissan s12 ca18et tachometer

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chester240
MS/Extra Newbie
Posts: 6
Joined: Wed Apr 29, 2009 5:56 am

Nissan s12 ca18et tachometer

Post by chester240 »

Hi.
I have problem trying to run my oem tachometer.
Originaly it was run by negative terminal of a single coil. But after i swaped the engine for ca18det i cant use this type of signal due to COP and wasted spark.
I have build this "thing"
Image
But the tacho works for like couple of seconds and then drops.
I have to give it some throtle to work again and it stops working at idle again after couple of seconds.
Im using MS2 3.57 extra nan JS4 for tacho output signal.
Regards
Maciej
seishuku
Experienced MS/Extra'er
Posts: 209
Joined: Tue Dec 01, 2009 5:38 pm
Location: Wisconsin, USA

Re: Nissan s12 ca18et tachometer

Post by seishuku »

You would be better off using the diode from each method, rather than letting MS drive the tach.
DaveEFI
Super MS/Extra'er
Posts: 4175
Joined: Sun Apr 15, 2012 12:55 am
Location: SW London, UK

Re: Nissan s12 ca18et tachometer

Post by DaveEFI »

chester240 wrote:Hi.
I have problem trying to run my oem tachometer.
Originaly it was run by negative terminal of a single coil. But after i swaped the engine for ca18det i cant use this type of signal due to COP and wasted spark.
I have build this "thing"
Image
But the tacho works for like couple of seconds and then drops.
I have to give it some throtle to work again and it stops working at idle again after couple of seconds.
Im using MS2 3.57 extra nan JS4 for tacho output signal.
Regards
Maciej
Good luck with any of the suggested circuits to do this. I had only partial success with all of them. I ended up replacing the electronics inside the tach for a modern circuit designed to work from a 12v signal. But it obviously depends on the design of the electronics in yours as different makers aren't identical. Mine is Smiths. With the suggested circuits, I had best results using the diodes one and adding a pull down resistor. But that would drop to zero above about 5000 rpm.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
chester240
MS/Extra Newbie
Posts: 6
Joined: Wed Apr 29, 2009 5:56 am

Re: Nissan s12 ca18et tachometer

Post by chester240 »

With diodes i will have another problem. When i hit the revlimiter or flatshift with a sparkcut the tacho will go nuts. I had this problem with stock engine (one coil and distributor). Thats why i wanted to use ms output.
chester240
MS/Extra Newbie
Posts: 6
Joined: Wed Apr 29, 2009 5:56 am

Re: Nissan s12 ca18et tachometer

Post by chester240 »

Ok figured it out today.
There was a small 1K Omh rezistor inside the relay that prevented the voltage spikes from the colapsing magnetic field in the relays coil. After removing it tachometer works like a charm. For now :)
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