General Miata Chat A place to talk about anything Miata

Creating a tach signal without coilpacks 94-95.5

Thread Tools
 
Search this Thread
 
Old 07-11-2018, 11:03 PM
  #1  
Junior Member
Thread Starter
 
2jz_mickey's Avatar
 
Join Date: Jul 2017
Posts: 73
Total Cats: 3
Default Creating a tach signal without coilpacks 94-95.5

Hi guys!

This is just theoretics but i think i figured out how to produce a tach signal without the 4 pin coil pacs amd without having to wire your cluster into you aftermarket ecu's tach out.

the cas sgt out is a 5v square signal.

The coil pack (tach) puts out a 12v square signal.

now my question is... What can be used to convert a 5v square wave inti a 12v square wave?
2jz_mickey is offline  
Old 07-11-2018, 11:33 PM
  #2  
SADFab Destructive Testing Engineer
iTrader: (5)
 
aidandj's Avatar
 
Join Date: Apr 2014
Location: Beaverton, USA
Posts: 18,642
Total Cats: 1,866
Default

A megasquirt
aidandj is offline  
Old 07-12-2018, 12:36 AM
  #3  
Junior Member
Thread Starter
 
2jz_mickey's Avatar
 
Join Date: Jul 2017
Posts: 73
Total Cats: 3
Default

Or am i overcomplicating things?

After some research i think it might also be possible to tap into the ignitor signal with a diode and a 1k ohm resistor (pullup) and feeding that into the wht/blk wire to create the tach signal. In other words simulate the tach driver within the coil.
2jz_mickey is offline  
Old 07-12-2018, 09:17 AM
  #4  
Boost Czar
iTrader: (62)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 79,493
Total Cats: 4,080
Default

yes you are.

why are you doing this?

what did you do where you no longer have a tach signal?

why would jerry-rigging diodes inside the engine bay be a better alternative to using the ******* tachout on your ECU?
Braineack is offline  
Old 07-12-2018, 10:19 AM
  #5  
Junior Member
Thread Starter
 
2jz_mickey's Avatar
 
Join Date: Jul 2017
Posts: 73
Total Cats: 3
Default

Originally Posted by Braineack
yes you are.

why are you doing this?

what did you do where you no longer have a tach signal?

why would jerry-rigging diodes inside the engine bay be a better alternative to using the ******* tachout on your ECU?
I want to attempt something different.

I will be swittiching to ls coils which don't provide a tach signal.

im not way ng its better im just trying to make a different way of attacking the problem.
2jz_mickey is offline  
Old 07-12-2018, 10:37 AM
  #6  
VladiTuned
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 35,821
Total Cats: 3,481
Default

y tho

different usually means dumb and redundant
18psi is offline  
Old 07-12-2018, 10:44 AM
  #7  
Junior Member
Thread Starter
 
2jz_mickey's Avatar
 
Join Date: Jul 2017
Posts: 73
Total Cats: 3
Default

Originally Posted by 18psi
y tho

different usually means dumb and redundant
It may be redundant but I doubt its dumb in this case.

I just would like to make the antique system work the way its meant to work. Personally i believe this is easier than pulling off my cebter console, runing a wire through my overcrowded dash, behind under the carpet, and tapping into an ecu pinnout.

Rather you make a simple circuit integrated into the harness that's already being made for the coils and you can revert to factory coil packs or COP setyps with ease!
2jz_mickey is offline  
Old 07-12-2018, 10:46 AM
  #8  
VladiTuned
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 35,821
Total Cats: 3,481
Default

lol wow. ok then

good luck
18psi is offline  
Old 07-12-2018, 10:48 AM
  #9  
Junior Member
Thread Starter
 
2jz_mickey's Avatar
 
Join Date: Jul 2017
Posts: 73
Total Cats: 3
Default

I get that you guys are trying to save me headaches and i appreciate that but i think this is something that might be worth it!
2jz_mickey is offline  
Old 07-12-2018, 11:05 AM
  #10  
Boost Czar
iTrader: (62)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 79,493
Total Cats: 4,080
Default

Originally Posted by 2jz_mickey
I get that you guys are trying to save me headaches and i appreciate that but i think this is something that might be worth it!
but if you ECU already provides the tachout, which also provides the sparkout which you would use for your tach, why build something at all? you're building a redundant circuit simply to not use a built-in function? I just don't get the logic.

turn tachout on.
send the tach signal to the white/black wire.
tie the white/black wire to the yellow/blue wire.
enjoy tach.

or:



here you have to:
tap spark A and Spark B.
put a diode on Spark A and Spark B tap.
Connect the taps to a zener diode connected to the yellow/blue wire.

this is basically doing the exact same thing, but requires extra messy wiring inside the engine bay.
Braineack is offline  
Old 07-12-2018, 11:14 AM
  #11  
Junior Member
Thread Starter
 
2jz_mickey's Avatar
 
Join Date: Jul 2017
Posts: 73
Total Cats: 3
Default

Thank you! I just prefer the short wiring in the bay
2jz_mickey is offline  
Old 07-12-2018, 06:00 PM
  #12  
mkturbo.com
iTrader: (24)
 
shuiend's Avatar
 
Join Date: May 2006
Location: Charleston SC
Posts: 15,176
Total Cats: 1,680
Default

The wire is already ran from your ECU connector to the back of the stock dash. You just need to make sure whatever way you are hooking up your MS has it.

As for wanting to run LS coils on the stock ecu, that is a bad idea long term due to dwell timings.
shuiend is offline  
Old 07-12-2018, 06:46 PM
  #13  
Junior Member
Thread Starter
 
2jz_mickey's Avatar
 
Join Date: Jul 2017
Posts: 73
Total Cats: 3
Default

Originally Posted by shuiend
The wire is already ran from your ECU connector to the back of the stock dash. You just need to make sure whatever way you are hooking up your MS has it.

As for wanting to run LS coils on the stock ecu, that is a bad idea long term due to dwell timings.
As far as im aware the tach on a 94-95.5 4pin coil pack does not go through the ecu.

Im not going to be running ls coils on the factory ecu
2jz_mickey is offline  
Old 07-12-2018, 08:51 PM
  #14  
Tweaking Enginerd
iTrader: (2)
 
Ted75zcar's Avatar
 
Join Date: Mar 2013
Location: Boulder, CO
Posts: 1,772
Total Cats: 353
Default

The connector containing the tach wire is right next to the hvac blower assembly under the dash, at least it is on a '91.
Ted75zcar is offline  
Old 07-13-2018, 06:52 AM
  #15  
Elite Member
iTrader: (6)
 
ryansmoneypit's Avatar
 
Join Date: Feb 2013
Location: A cave in Va
Posts: 3,395
Total Cats: 456
Default

I have a 95, with Las coils. I didn't have to do any of this. You have to run a vacuum line to mas, so just use that route for the ONE wire.
ryansmoneypit is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
IcantDo55
General Miata Chat
15
12-13-2017 04:44 AM
matthewdesigns
ECUs and Tuning
26
11-09-2011 10:56 AM
miatamike203
MEGAsquirt
4
05-08-2011 10:49 AM
Sean
General Miata Chat
14
11-22-2010 11:48 AM
jeff_man
General Miata Chat
2
06-30-2010 09:50 PM



Quick Reply: Creating a tach signal without coilpacks 94-95.5



All times are GMT -4. The time now is 08:28 PM.