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Old 08-09-2010, 11:01 PM   #1
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Default Megasquirt Tach input Sheild.

All,

Your advice has been very helpful.

I came up with another question.

Is it necessary to run a shielded wire on th boomslang harness configuration? I know shielding is nice when outputting to a live coil, but in our case, it seems unnecessary. Since it's a hassle.. Can't it just be standard wire?

TIA
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Old 08-09-2010, 11:09 PM   #2
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no shield.
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Old 08-09-2010, 11:33 PM   #3
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Thanks!

A Couple more questions

The Thick Gray CAS (96-97 pin 4F) goes to 26 on the megasquirt. Right? I assume this is 5Vref.

The OEM NB. What does NB stand for? I assume this is the idle control valve and goes from 96-97 pin 3c to megasquirt pin 30 with a 1N4001 diode across it and +12V.

If I am not doing a fan control mod with a boomslang harness do I still need the bl/wht pin 27 connected to the factory harness?

If i don't yet have launch control setup should I connect the clutch to pin 29?

Does the Brown ignitor wire (4R) go to pin 36 of the megasquirt?

TIA!
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Old 08-10-2010, 12:28 AM   #4
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Quote:
Originally Posted by heychris View Post
The Thick Gray CAS (96-97 pin 4F) goes to 26 on the megasquirt. Right? I assume this is 5Vref.
Pin 4F at the ECU harness (a white wire in the OEM harness) is the CKP (CranKshaft Position) signal, which is the primary trigger. This goes to pin 24 of the MS.

Pin 4G at the ECU harness (yellow/blue) is CMP, or CaMshaft Position, the secondary trigger, which is typically wired to pin 25 of the MS, and then picked up at the IAC1A pad internally and wired to the CPU.

+5 Vref (pin 26) does not go to the CAS at all. This is used only for TPS or other analog potentiometer-based sensors which require a stable reference.



Quote:
The OEM NB. What does NB stand for?
In the context of a Miata, NB typically specifies the second-generation body style, produced from 1999 through 2005.

In the context of engine management, it might also refer to NarrowBand, aka the factory exhaust O2 sensor. This would be as opposed to a wideband sensor such as the Innovate LC1 or AEM UEGO.

Quote:
I assume this is the idle control valve and goes from 96-97 pin 3c to megasquirt pin 30 with a 1N4001 diode across it and +12V.
The IAC valve is at pin 4Q of the stock harness.

Pin 3C of the stock harness is one side of the narrowband O2 sensor signal, which is useless if you are planning to run a wideband sensor.


Quote:
If I am not doing a fan control mod with a boomslang harness do I still need the bl/wht pin 27 connected to the factory harness?
Boomslang, as in a parallel install? If so, you can let the stock ECU run the fans if you wish.

Quote:
If i don't yet have launch control setup should I connect the clutch to pin 29?
You can do whatever you want with it.



Quote:
Does the Brown ignitor wire (4R) go to pin 36 of the megasquirt?
It can, so long as you also configure the wheel decoder backwards to match.
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Old 08-10-2010, 01:26 AM   #5
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Wow.. that would have been bad if I hadn't asked.. Thanks again

My installation is parallel.

Quote:
+5 Vref (pin 26) does not go to the CAS at all. This is used only for TPS or other analog potentiometer-based sensors which require a stable reference.
Is the stock ECU suitable for handling the +5 Vref? Should I ignore this on a parallel installation?

Quote:
Quoteoes the Brown ignitor wire (4R) go to pin 36 of the megasquirt?
It can, so long as you also configure the wheel decoder backwards to match.
Does this mean if I connect grn/wht (4N) to pin 31 I don't need to connect anything to pin 36?


Also I noticed that the miataturbo wiki ( http://miataturbo.wikidot.com/MS2_a ) doesn't show a capacitor on the tach for MS2 although it does show it for MS1. Is this an oversight or is it not recommended to do the capacitor on an MS2?
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Old 08-10-2010, 09:09 AM   #6
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Quote:
My installation is parallel.
You should really go standalone and MS-II.

Quote:
Is the stock ECU suitable for handling the +5 Vref? Should I ignore this on a parallel installation?
yes.

Quote:
Does this mean if I connect grn/wht (4N) to pin 31 I don't need to connect anything to pin 36?
yes


Quote:
Originally Posted by heychris View Post
Also I noticed that the miataturbo wiki ( http://miataturbo.wikidot.com/MS2_a ) doesn't show a capacitor on the tach for MS2 although it does show it for MS1. Is this an oversight or is it not recommended to do the capacitor on an MS2?
No need for it on MS-II. I hope you're building an MS-II and not an MS-I, I gotta get people off MS-I.
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Old 08-10-2010, 09:14 AM   #7
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Thanks!!

I am building an MS-II. This is just a precursor to building an MS-III. I figured I'd get my feet wet with a parallel install first.

On an Off topic question. I'm also working on a 1970 BMw 2002. It seem to me that the ignition it well set up on a miata. I may just use a coil pack from a miata for that install to save myself from COP headaches and EDIS nightmares.
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Old 08-10-2010, 09:19 AM   #8
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almost everyone with MS and a miata converts to COPs.

fwiw, ms-III will be as simple as pulling the MS-II board and plopping in the MS-III, I still suggest standalone...the only reason for parallel is for emissions for you ODB-II folks
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Old 08-10-2010, 12:59 PM   #9
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Quote:
Originally Posted by Braineack View Post
Quote:
Does this mean if I connect grn/wht (4N) to pin 31 I don't need to connect anything to pin 36?
yes.
Wait, what??


First off, I thought we were talking about a '96 here. There's no green/white wire at position 4N of the ECU- that's a brown/yellow wire.

And second, you need to connect lines to both pin 31 and pin 36 of the MS, as these are the two ignition output channels (assuming you've built the spark out mods to the usual DIY spec.) And they'll need to connect to both terminals 4N and 4R of the stock ECU harness, as these are the two lines which drive the ignition coils.

Unless I'm totally misunderstanding something here...
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Old 08-10-2010, 01:09 PM   #10
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This is a 96? A standalone type installation would be easier than parallel. There's nothing important on this motor that the MegaSquirt is unable to handle.

Shielded tach wiring is better than unshielded, and is what I'd recommend. However, I didn't use shielded wiring on my own install.
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Old 08-10-2010, 01:12 PM   #11
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Joe,

You are right this is a 97.

Ok.. I get it now the picture above shows the stock harness and the color (brown) indicates it should be connected to pin 36 of the megasquirt. Pin 36 of the DB37 goes to 4R

The green/white from pin 31 attaches to 4N

What threw me off is the megasquirt db37 shows brn/gry




Again thanks. I'd be in trouble without your help.
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Old 08-10-2010, 01:41 PM   #12
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Ok, I get it now. You're using color codes from one of the many "how to pin a db37" writeups...

Be careful when doing that. Those images are all just the product of someone's opinion of how it should be done, so there's likely to be some variance from one to another. Those color codes should correspond to what you get if you order DIY's "bundle-o-wire" kit, but even within that there's some duplication- last I checked, that kit gave you two green/white wires and two white/blue wires.

So let me be clear. When I refer to a wire color, I am referring to the color of the wire in the car's original ECU harness. You can use nothing but black wire to make all the connections to the MS for all I care.

ALSO, be aware that a lot of the pin designations on the DB-37 do not have fixed functions. They merely go to internal pads, and then from there you have to cross-connect them to something useful, which usually involves building a small circuit. Examples of this include the four "IAC" pins (25, 27, 29, 31), the "IGN" pin (36) and the four "SPR" pins (3, 4, 5, 6). So whenever somebody tell you to hook a wire to one of those, be sure you understand that you've also got to do some work inside the MS to make it useful.


As to the "tach" wire (pin 24 to the CAS) and the shielded vs. non-shielded debate: using shielded wire here is of no benefit at all. Why is this? Because the wire you're connecting to in the stock harness is unshielded.


And I'm with Ben insofar as a standalone install being simpler than a parallel.
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