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Creating a tach signal without coilpacks 94-95.5

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Creating a tach signal without coilpacks 94-95.5

 
Old 07-11-2018, 11:03 PM
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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?
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Old 07-11-2018, 11:33 PM
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A megasquirt
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Old 07-12-2018, 12:36 AM
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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.
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Old 07-12-2018, 09:17 AM
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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?
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Old 07-12-2018, 10:19 AM
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Originally Posted by Braineack View Post
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.
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Old 07-12-2018, 10:37 AM
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y tho

different usually means dumb and redundant
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Old 07-12-2018, 10:44 AM
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Originally Posted by 18psi View Post
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!
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Old 07-12-2018, 10:46 AM
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lol wow. ok then

good luck
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Old 07-12-2018, 10:48 AM
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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!
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Old 07-12-2018, 11:05 AM
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Originally Posted by 2jz_mickey View Post
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.
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Old 07-12-2018, 11:14 AM
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Thank you! I just prefer the short wiring in the bay
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Old 07-12-2018, 06:00 PM
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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.
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Old 07-12-2018, 06:46 PM
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Originally Posted by shuiend View Post
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
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Old 07-12-2018, 08:51 PM
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The connector containing the tach wire is right next to the hvac blower assembly under the dash, at least it is on a '91.
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Old 07-13-2018, 06:52 AM
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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.
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