johnny3986

I need to know if:

A) our tach output wire is connected to the coil (like it has an individual coil per wire)

B) The tach wire is connected to the tach from the engine electronic controller

or I know it isn't possible (but these directions listed it)

C) coil packs that fire in pairs and the the tach wire is connected to the coil.


It is a stock ignition system for those that might be wondering.

Thanks you guys!! You are indirectly helping me hook up my N20...

Colin91Z

I think I can answer A) for ya, the tach output wire is the white one coming off of the Ignition control module, this is where my auto meter tach get its reading from anyway...

johnny3986

Where is the ignition control module located at?

Does this seem right to everyone else?

Injuneer

The stock tach is driven off the PCM pin A13. The white wire on the ICM connects to pin B5.

When you need wiring diagrams, or photos showing component locations, use Shoebox's website:

http://shbox.com/1/coil_loc.jpg

http://shbox.com/1/4th_gen_tech1.html

Colin91Z

Ok so does this mean I should change where my tach is getting its signal from to the A13 pin then? I was told by autometer that the white wire that I was refering to is where to get the signal from, are they right or wrong?

For the record, my tach seems to work fine...as far as I know anyway, but is nowhere near cosistant with my factory tach. I always just assumed that the factory one was off a bit and the autometer was dead on...could it be the other way around?

GetaZforgetGT

Factory tach normally stands a few hundred RPM higher than what the PCM is actually reading.

IE PCM sees 2500 rpm but tach may read 2800.

This is the case on my car for sure and many others have said the same thing.

Injuneer

You're going to get a similar signal from either pin.

WS Sick

I have wired tachs from both locations and they read pretty well the same thing. Its cleaner and easier though just to take the white PCM lead (from PCM) since its already under the dash.

Colin91Z

Ok well I think I'll just leave mine way it is if its not gonna make a difference, being as its loomed neatly out of sight and everything. Thanks for the advice

johnny3986

So take it off the computer, but is it A, B, or C?

'A' has been answered

But 'B' seems more likely now though...

93DGTA

Is this true on a 93 also? Trying to track this info down getting ready to put auto meter in with shift light

shoebox

The white wire in cavity "B" of the ICM plug will probably work. However the 1993 tach gets its feed directly from another white wire on the coil plug that later years do not have. That wire has a little filter on it.

If you access C230 under the RH kick panel, you can tap into cavity "D" (same white wire coming from the 1993 coil) that feeds the factory tach. That will keep you from having to run a wire under the hood.
C230, cavity "D" is the tach feed for any 93-97, regardless of whether it comes from the coil or PCM.

93DGTA

Ok thanks

Kory 88 Iroc Lt-1

Thanks for the info. I was looking for this.
Kory

shoebox

Kudos for finding it with the search!