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S12 Technical Areas => Engine Tech => ENGINE (OEM): CA18DET Tech => Topic started by: lmedeiros on 01:15:24 PM / 31-Aug-06

Title: Using The S12 Tacho?
Post by: lmedeiros on 01:15:24 PM / 31-Aug-06
Who has hooked up the s12 tacho, and how did you do it? What did you use to do it, parts ect...?

Oh yeah I used to have a 87 w/ the ca20 before I did the swap incase that matters.
Title: Using The S12 Tacho?
Post by: S12 Drifter on 04:27:11 PM / 31-Aug-06
well there is the theory of running the four diodes off the igniter but I do not know of anyone that has done this...   I too would like to know if anyone has gotten their tach to work
Title: Using The S12 Tacho?
Post by: sam31183 on 05:09:09 PM / 31-Aug-06
I think gerrybg did it...he is the one who said how to use the diodes. Also, pukkasilvia may have done this to.
Title: Using The S12 Tacho?
Post by: S12 Drifter on 11:01:32 PM / 31-Aug-06
Quote from: sam31183
I think gerrybg did it...he is the one who said how to use the diodes. Also, pukkasilvia may have done this to.


http://www.club-s12.org/forums/index.php?s...amp;hl=s12+tach (http://club-s12.org/v3/index.php?topic=14119&hl=s12+tach)


All bow down to the search button!!
Title: Using The S12 Tacho?
Post by: sam31183 on 11:42:25 PM / 31-Aug-06
yah, I actually copied and pasted what gerry wrote into my write up...
Title: Using The S12 Tacho?
Post by: S12PSI on 02:29:53 AM / 03-Sep-06
I haven't tried it yet, but whats wrong with hooking up the Tach Signal wire from the ECU (its red and yellow, number 7 i think, i have the wiring diagram somewhere) straight to the Tacho?

Anyone tried that, reasons why it won't work etc. Rather than hacking into your wiring in the engine bay.
Title: Using The S12 Tacho?
Post by: Indecisive on 12:02:20 PM / 03-Sep-06
the reason is explained in that thread(actually, I dont' know which thread that is...but if it's the same one I found a few weeks ago, it's in there)

basically, the signal on the stock motor is very high, but the one on the ca18det is very low.  Too low to actually run the speedometer.
Title: Using The S12 Tacho?
Post by: Paul on 11:17:39 PM / 03-Sep-06
could you run a sort of line amplifier to boost the signal?
Title: Using The S12 Tacho?
Post by: gerrybg on 01:10:40 AM / 04-Sep-06
You could muck around trying to boost the signal which I did with no success that's why I used the diode method and my factory tach runs fine.

As you can see in the pic below I have a redtop sr, but its exactly the same for the ca8det, (early red top sr's and ca18det's have the same wiring)
Title: Using The S12 Tacho?
Post by: gerrybg on 01:39:34 AM / 04-Sep-06
(http://www.picturerack.com/ims/gerryb/srs12/62560.jpg)
Title: Using The S12 Tacho?
Post by: gerrybg on 02:25:33 AM / 04-Sep-06
(http://img96.imageshack.us/img96/9881/dioderx3.png)
Title: Using The S12 Tacho?
Post by: gerrybg on 02:42:39 AM / 04-Sep-06
Here's a pic of the ca18det ignitor, the 4 wires that go to the coilpacks from this are the ones you splice 4 diodes onto then join the "cathode" (striped) ends together and join them to one wire which you run to your tacho. There is a light green wire at the back of the tacho, which you cut and join to this wire. You have to remove the instrument panel to get at the connector that has the light green wire in it.
(Value of the diodes is stated in the other post linked further up, you get them from radioshack or similar)

Jeez you guys are lucky its all there spoon fed for you!!

(http://img171.imageshack.us/img171/637/ignitorpicna4.th.jpg)
Title: Using The S12 Tacho?
Post by: Indecisive on 11:14:29 AM / 04-Sep-06
and to make it even more spooon fed...I'm gonna pin it.

Thanks Gerry...you provided more than what was expected.
Title: Using The S12 Tacho?
Post by: S12PSI on 08:36:33 PM / 04-Sep-06
I think the hard part is getting to the back of the tacho to make this all happen haha, i haven't yet pulled the dash out.

When u say the signal is too weak, i think its more a case of the signal only being half as often as it needs to be, i spliced into the wire of 1 of my coil packs i think at first for my Aftermarket tacho, and it sort of worked but it was only 1/4 of what it should have read, meaning it was only getting 1/4 of the signal it needed, I'm not wiring expert here but the original S12 had 8 plug leads, perhaps the signal you guys have tried just doesn't get sent often enough.

I really haven't looked at the back of my tacho as i said, but if u split the signal from the tacho feed wire, using the same cathode/diodes explained perhaps this would help.

Not trying to harp on a dead lead here but anythings better than hacking into your wiring harness. Perhaps someone has already tried this, i dunno. Anyone tried using an S13 tacho driver?
Title: Using The S12 Tacho?
Post by: ferret on 05:37:50 PM / 08-Sep-06
There is a tacho signal straight out of the ecu which should run your aftermarket tacho, it just doesn't provide enough voltage to drive the S12 tacho. I read on a bluebird (another ca20 powered aussie car) forum that one of the guys there got his tacho working by using the tacho output from the S13 ecu and pulling the voltage up using a +12v wire with 2k ohm resistor inline, and then splicing this into tacho output from the ecu before connecting it to the  tacho. I haven't tried it so I don't know if it will work or not.
Title: Using The S12 Tacho?
Post by: Fester on 09:13:10 PM / 08-Sep-06
The tacho works by counting the rate at which ignition pulses are being fired.  With the CA20 (and distributor-based ignition systems in general), all four pulses are on a single wire, so all four pulses are counted by the tacho.  With the CA18/SR20 (and distributor-less ignition systems in general), each pulse is on its own seperate wire so any given wire carries only 1/4 the pulses of a distributor system, like so:

CA20    _|-|___|-|___|-|___|-|___
CA18#1  _|-|_____________________
CA18#2  _______|-|_______________
CA18#3  _____________|-|_________
CA18#4  ___________________|-|___

So, you should get 1/4 the tacho reading from a CA18 that you do from a CA20

To complicate things, some ignition systems (like my Microtech) fire "waste sparks", i.e. they fire on the exhaust stroke as well as the ignition stroke.  Supposed to make it burn cleaner and produce more power or something.  That looks like this:

WS#1    _|-|_________|-|_________
WS#2    _______|-|_________|-|___
WS#3    _|-|_________|-|_________
WS#4    _______|-|_________|-|___

With a waste spark system, you should get 1/2 the tacho reading from a CA18 that you do from a CA20.

What the diodes that Gerry has suggested do is to allow you to mix the signals from the CA18 wires onto a single wire, without affecting the original signals.  The output from the junction of the [edit]cathodes[/edit] of the diodes then looks like the CA20 ignition signal:

_|-|___|-|___|-|___|-|___

so the tacho is happy and displays what you want.

As someone else noted, you can also use the output of an aftermarket (or even factory CA18) ECU, with some additional circuitry to increase the signal to the right voltage level.  While it would appear that a pullup resistor works, personally I wouldn't trust it.  I would put a proper level shifter circuit in - but that's a bit of work to do right so its easiest just to use the diodes imho.
Title: Using The S12 Tacho?
Post by: Indecisive on 09:39:18 PM / 08-Sep-06
wow...I never understood why having 4 diodes works.  Thank you VERY VERY much Fester for explaining it.  I like things to work, but I love it when I know WHY they work.  

Title: Using The S12 Tacho?
Post by: gerrybg on 09:02:55 PM / 09-Sep-06
Australian made nissan Pintaras/skyline R31's use Australian made VDO guages which are different to the s12 Japanese made ones. I have used a resistor to boost ("pull up") the signal from the ECU tacho feed to get a factory tacho working in one of these cars with an SR transplant for a friend, its easy.

I( also did this for a guy with a bluebird (910 - 85 model) with an sr transplant, (from the bluebird forums Fester is talking about, probably the same guy as he is well known on those froums and posts a lot) and got his factory tacho working. The bluebird was also an Australian made nissan and also had VDO Australian made guages.

Unfortunately this method doesn't work with the s12 tacho,(as they use guages made by a Japanese guage maker and require a different signal) I know I tried a million different ways to get it working from the ECU feed with resistors and couldn't. Sorry guys but STOP FLOGGING A DEAD HORSE!!!!!

The diode method works perfectly and its piss easy, As far as I remember there is only 4 wires or so coming out of the ignitor to the coilpacks. There is nothing to it!!!! You don't have to bare  all your loom or anything, just this one small area and then retape and shrinkwrap it,(about three inches of it with only these 4 or 5 wires in it for god sake) JUST DO IT!!

And yes if you only hook up the wire to 1 coil pack you will only get 1/4 the signal 1 coilpack signal = 1 firing plug, 4 coilpack signals = 4 firing plugs (4/4) hence the use of 4 diodes so you can join the signals together(from the ignitor shown in the picture in the above post) together and get a full signal.(Which is what Fester has eloquently explained above) This is exactly what diodes are used for in electronics. THEY ONLY LET CURRENT FLOW IN ONE DIRECTION!!!.........

And so you don't have to follow the other link to get the diode values I looked it up for you:

 "1N4004"

(Grumpy old bastard aren't I!!)
Title: Using The S12 Tacho?
Post by: Fester on 09:39:44 PM / 09-Sep-06
Its actually a 1N4004
Title: Using The S12 Tacho?
Post by: Indecisive on 11:36:51 PM / 09-Sep-06
any REAL electronics store will have these diodes, and probably of higher quality of the radio shack stuff, and for pennies.  

Then again, if you don't know where to get them, or if it's too much hassle, you should be able to get them at radio shack.
Title: Using The S12 Tacho?
Post by: Keith on 03:14:48 PM / 10-Sep-06
Are they just called "diodes"? Do they need to be a specific wattage or voltage?
Title: Using The S12 Tacho?
Post by: Philipn126 on 03:51:20 PM / 10-Sep-06
i know im in the wrong section, but do you guys think this will work with us ka swappers?
Title: Using The S12 Tacho?
Post by: Fester on 06:32:58 AM / 11-Sep-06
Quote from: Keith
Are they just called "diodes"? Do they need to be a specific wattage or voltage?

iirc the 1N4004 is a 1 amp 400 volt rectifier diode.  They're as common as dog turds.  If you're looking for an alternative, I wouldn't use a signal diode, but any reasonably rated rectifier should be fine.  Bear in mind that you're working around the ignition which can have sizeable voltage transients (caused by backlash from the coils) so a 400V rating is not unreasonable.

Quote from: Philipn126
i know im in the wrong section, but do you guys think this will work with us ka swappers?

If they use the same setup as a CA18DET, i.e. 4 coils and electronic spark distribution, then yes it should work.
Title: Using The S12 Tacho?
Post by: Indecisive on 11:14:38 AM / 11-Sep-06
I'm pretty sure the KA has a distributor...but I could be wrong.
Title: Using The S12 Tacho?
Post by: hillkill on 10:13:30 PM / 12-Sep-06
ALright am I the only one who's had problems with the diode thing? I had my tach working for about 2 months using the 4 diodes but the tach seemed a little sluggish up in the higher rpms. I never really trusted it if you know what I mean and then out of nowhere my car starts sputtering and dies. I find out that the diodes were fried and the bad connctions of the broken diodes were causing my ignition to misfire. I replaced the diodes only to have them last for another 3 months before the same thing happened. I eventually gave up haveing a non trustwothy tach. I now have a safc2 that I use but I dont get a proper 4th or 5th gear rpm due to the chip I have in the ecu.  I still want a reliable tach but dont really want a monster tach.
Title: Using The S12 Tacho?
Post by: Fester on 03:16:35 AM / 13-Sep-06
What actually died in the diodes?  Did they give up mechanically, e.g. leads snapping due to vibration, or did they die internally due to over-voltage or over-current?
Title: Using The S12 Tacho?
Post by: gerrybg on 04:02:54 AM / 13-Sep-06
Yeah let u know coz I've had mine going fine for 2 months with the diodes,(I got it working ages ago but hadn't finished my body work etc so didn't really drive it much until the last 2 months) but yours is 3 months, we need to know any negatives like this to watch out for.
Title: Using The S12 Tacho?
Post by: hillkill on 03:44:19 PM / 13-Sep-06
For both times the diodes were snapped or on there way to snapping. The second time I even mounted them onto a board with hot glue to resist vibration.
Title: Using The S12 Tacho?
Post by: Keith on 03:56:03 PM / 13-Sep-06
Quote from: hillkill
For both times the diodes were snapped or on there way to snapping. The second time I even mounted them onto a board with hot glue to resist vibration.
What voltage rating were they?  Fester mentioned using a 400 volt rating diode
Title: Using The S12 Tacho?
Post by: Fester on 07:07:35 AM / 14-Sep-06
It sounds like it was a mechanical failure rather than an electrical one.  Try mounting the diodes rigidly on a solid surface with light, flexible multistrand wire in and out of the circuit.  Hot melt glue over the junctions of wire and circuitry should help to protect things as well (soldered junctions are notoriously prone to failure due to vibration).  The less weight that can flop around, the less chance there is of a mechanical failure.
Title: Using The S12 Tacho?
Post by: Premo on 07:39:33 PM / 12-Nov-06
this might interest you guys doing this swap



clicky (http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=127/category_id=287/home_id=59/mode=prod/prd127.htm)
Title: Using The S12 Tacho?
Post by: Fester on 02:03:45 AM / 13-Nov-06
That's the right answer all right Premo.  Its not even particularly expensive.
Title: Using The S12 Tacho?
Post by: sam31183 on 02:30:51 PM / 13-Nov-06
intriguing. Any alternative to having an giant monstrous ricer tach i am all up for.


"Hot rice exits here!"
*points at 626 tail pipe*
Title: Using The S12 Tacho?
Post by: SR20D21 on 09:57:31 PM / 28-Dec-06
Quote from: hillkill
ALright am I the only one who's had problems with the diode thing? I had my tach working for about 2 months using the 4 diodes but the tach seemed a little sluggish up in the higher rpms. I never really trusted it if you know what I mean and then out of nowhere my car starts sputtering and dies. I find out that the diodes were fried and the bad connctions of the broken diodes were causing my ignition to misfire. I replaced the diodes only to have them last for another 3 months before the same thing happened. I eventually gave up haveing a non trustwothy tach. I now have a safc2 that I use but I dont get a proper 4th or 5th gear rpm due to the chip I have in the ecu.  I still want a reliable tach but dont really want a monster tach.


I have been using the diode method for years and i have never had a problem.(There is a car that I did 5 years ago on the same diodes) Unless you have a malfunction you should not be frying diodes.
You said your tach was slugish....that may be pointing to your problem? You may be pulling to much current to drive the tach do to a malfunction that did not show up with the stock set up?? shorted wire after the diodes?? I don't know. You can increase the amp rating of the diode with no problems to the signal BUT I would check it out before doing this as I have never fried ANY diodes?? I have used higher rated diodes when the local electrical supply was out of stock with no problems.
 
But again I would look into your particular set up sounds as though there is a problem.


Quote from: Fester
That's the right answer all right Premo.  Its not even particularly expensive.

Compared to 4 diodes, solder and heat shrink at less then $5 dollars , $80.00 dollars is very expensive! Save that money and put it into somthing worth it or buy a tank of fuel with the money you will save
Title: Using The S12 Tacho?
Post by: Keith on 07:43:16 PM / 12-Jan-07
Instead of tapping in the wire you run from the diodes to the green tach wire behind the cluster.......can you simply run the diode wire to the tach signal wire in the engine bay that leads from the original primary coil transistor?  It's blue, I think.....and I still have this part of the s12 harness in my engine bay
Title: Using The S12 Tacho?
Post by: Keith on 03:57:08 PM / 31-May-07
Quote from: Keith
Instead of tapping in the wire you run from the diodes to the green tach wire behind the cluster.......can you simply run the diode wire to the tach signal wire in the engine bay that leads from the original primary coil transistor?  It's blue, I think.
To answer my own question.............yes it works this way.  FINALLY got mine wired up....and works great
Title: Using The S12 Tacho?
Post by: sam31183 on 01:13:15 AM / 01-Jun-07
keith! I need pics and a write up! pretty please. I will add it to my write up and give you full credit. Because...well, your the man!
Title: Using The S12 Tacho?
Post by: Keith on 03:37:14 AM / 02-Jun-07
Quote from: sam31183
keith! I need pics and a write up! pretty please. I will add it to my write up and give you full credit. Because...well, your the man!
Hmmmmmmmm, well, I've already got everything taped up......but I'll snap some pics of everything anyways......and write-up. I followed Gerrys instructions though......only thing different I did was wire them to the gauge  signal wire in the engine bay instead of tapping into the wire behind the cluster.
Give me a coupe of days...........
Title: Using The S12 Tacho?
Post by: Sharas on 01:28:06 AM / 11-Oct-07
Hm... Now i was wondering has anybody tried using the tach signal wire runing from the ca18det ecu?
Title: Using The S12 Tacho?
Post by: Ozchuck on 10:15:20 AM / 11-Oct-07
If you had read the thread, you would have seen:

"
basically, the signal on the stock motor is very high, but the one on the ca18det is very low. Too low to actually run the speedometer.
"

Lots of cutting and slicing to amplify the signal.

Buy 4 diodes, part with $5, move on.
Title: Using The S12 Tacho?
Post by: Sharas on 02:52:15 PM / 11-Oct-07
I have no prob with the diodes or the $5, but i just dont like the idea of more wires being sliced and resoldered under the hood. To many already.
Title: Using The S12 Tacho?
Post by: Ozchuck on 08:04:06 AM / 13-Oct-07
It'll be fine, just do it
Title: Using The S12 Tacho?
Post by: jeffwins24 on 07:24:08 PM / 28-Mar-08
is there any way at all to use the digi dash? what if i we're to rewire it would that work?
Title: Using The S12 Tacho?
Post by: gerrybg on 07:58:48 PM / 28-Mar-08
Try the method and see if the digi tach runs with it!
Title: Using The S12 Tacho?
Post by: dwardle on 09:53:23 AM / 26-Sep-09
Sorry for reviving an old thread, but it's the most appropriate.

I had my SR20det running fantastic in my mk2 s12, then I spliced in 4 diodes, hooked them to a wire to my tach, and now it runs like crap and won't rev at all.

ANY HELP?
Title: Using The S12 Tacho?
Post by: mod_mastaz on 08:02:12 PM / 26-Sep-09
You probably have the diodes running the wrong way. The diodes purpose is to allow electricity to go in one direction only. If you wired it backwards, you pretty much just jumped ignition coils 1-2-3-4 all together and they all spark at once. Fix it before you kill your igniter.

Oh and this method does work with the digidash. Mine has been working for over a 6 months in CA heat and everything. I haven't cracked the diodes or had my car run like shit yet. They are the crappy radioshack ones too.
Title: Using The S12 Tacho?
Post by: dwardle on 08:58:28 AM / 09-Oct-09
They weren't wired the wrong way, strip was towards the tach end.  However I'm wondering if they weren't the right type/size of diode?

The tach was working fine, but the engine was not running at all barely.

Title: Using The S12 Tacho?
Post by: mod_mastaz on 01:49:34 PM / 10-Oct-09
Make sure they aren't contacting BEFORE the diode also. Remember to shrink wrap or wrap it in electrical tape. Does the car run better when the diodes aren't hooked up? Maybe there's an electrical issue not related to the tach.
Title: Using The S12 Tacho?
Post by: dwardle on 10:21:08 AM / 11-Oct-09
Car runs awesome without the diodes hooked up.  I ensured they were fully wrapped so there was NO contact before the diode.  I'm guessing they just weren't strong enough diodes.
Title: Using The S12 Tacho?
Post by: mod_mastaz on 12:10:28 AM / 12-Oct-09
Hrm.. quite possibly. You can try a higher amp/voltage diode and see if that helps.
Title: Using The S12 Tacho?
Post by: dwardle on 07:50:45 AM / 17-Oct-09
My bad, I was using the wrong diodes.  Make sure to use the 1N4004!  Tach works like a dream now along with the rest of the car.  

Getting the diff welded this week sometime so I can stop destroying my spider gears
Title: Using The S12 Tacho?
Post by: Navy_Mech2 on 08:05:45 AM / 17-Oct-09
Curtosey of the first page  
Quote from: Fester
Its actually a 1N4004
Title: Using The S12 Tacho?
Post by: chad-s12-drift on 10:24:00 PM / 20-Jan-10
Quote from: gerrybg
Here's a pic of the ca18det ignitor, the 4 wires that go to the coilpacks from this are the ones you splice 4 diodes onto then join the "cathode" (striped) ends together and join them to one wire which you run to your tacho. There is a light green wire at the back of the tacho, which you cut and join to this wire. You have to remove the instrument panel to get at the connector that has the light green wire in it.
(Value of the diodes is stated in the other post linked further up, you get them from radioshack or similar)

Jeez you guys are lucky its all there spoon fed for you!!

(http://img171.imageshack.us/img171/637/ignitorpicna4.th.jpg)
on the ignitor im trying to figure out what side to tap into i noticed on it there is an arrow pointing toward an edge if that arrow is pointed up would i tap into the left clip or right clip or if someone could tell me the wire colors i think both sides had different colors
Title: Using The S12 Tacho?
Post by: mod_mastaz on 06:58:03 AM / 22-Jan-10
Tap into the side before the igniter. That's the signal you need to combine for the stock tach to work. Don't forgot the diodes also!
Title: Re: Using The S12 Tacho?
Post by: Gnome on 10:14:10 PM / 23-Mar-14
Just about to attend to this tacho problem myself after checking into this string many months ago. Let's just say the whole engine transplant has been a major episode with considerable time and frustration getting the ECU sorted and the engine finally back on the road …only to have to do it all over again with a new ca18 rebuild when the former sounded like castanets and was definitely not environmentally friendly. Thanks to those who have provided what seems to be well considered info. I'm no electronics wiz, so I'll be getting a local auto elec to get it done and give him the thread to get him in the zone. I'll post my results, one way or the other.
Title: Re: Using The S12 Tacho?
Post by: Fhu on 06:07:25 PM / 15-Aug-14
Thanks for this thread
My Eur Tacho is alive :)