Where on the block is the ECU ground? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 07-25-2007, 03:54 PM   #1
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Default Where on the block is the ECU ground?

So another question about installing my LC-1...

Where on the block is the ECU ground that I'm supposed to use since Innovate and DIY Autotune highly recommend using a common ground with the Megasquirt to guarantee zero voltage differential?? Not only that, but don't I need 2 grounds to keep the system ground separate from the heater and analog grounds?

m2cupcar thinks that the stock ECU grounds to the chassis of the car.. which I haven't confirmed yet. Is that true for a '95 1.8?

And that brings me to another question. Flyin Miata has in their ECU instructions a method to get a "better" ground for the ECU in which they take pins from the Miata's stock wiring harness and reground them to somewhere in the engine bay. Is that something that we MS guys are doing?

Just confused..... Main question is... WHERE in the engine bay do I ground the LC-1 to get a common ground with the ECU (using the stock Miata wiring harness)??
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Old 07-25-2007, 04:02 PM   #2
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i grounded mine right to the ecu ground...i have no issues.

but there should be two on the rear passenger side, one is the rear lift hook guy, and the other below that.

the driver side around where the dipstick tube is, the ground goes to just under the brake booster.
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Old 07-25-2007, 04:26 PM   #3
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Originally Posted by Braineack View Post
i grounded mine right to the ecu ground...i have no issues.

but there should be two on the rear passenger side, one is the rear lift hook guy, and the other below that.

the driver side around where the dipstick tube is, the ground goes to just under the brake booster.
so those locations are actually where the ECU wires ground? That's the requirement I'm trying to make sure I fulfill.
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Old 07-25-2007, 04:28 PM   #4
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Quote:
Originally Posted by Braineack View Post
i grounded mine right to the ecu ground...i have no issues.

but there should be two on the rear passenger side, one is the rear lift hook guy, and the other below that.

the driver side around where the dipstick tube is, the ground goes to just under the brake booster.
The ECU grounds - all 5 of them in a distribution block - are on the chassis under your brake booster (washer bottle for me)
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Old 07-25-2007, 04:38 PM   #5
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The ECU grounds - all 5 of them in a distribution block - are on the chassis under your brake booster (washer bottle for me)
Thank you.
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Old 07-25-2007, 05:39 PM   #6
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For those with a 1.6L where is the engine ground for the ECU for us? Also do both the LC-1 grounds go to the same place?
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Old 07-25-2007, 06:02 PM   #7
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For those with a 1.6L where is the engine ground for the ECU for us? Also do both the LC-1 grounds go to the same place?
the instructions say that there are three ground wires: a system ground (white), a heater ground (blue), and the analog ground (green)

All the grounds need to share ground with the ECU to guarantee zero voltage difference between the two systems (ECU and LC-1), BUT the blue ground needs to separate from the white and green to prevent ground noise.
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Old 07-25-2007, 06:19 PM   #8
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its a black wire with a green stripe on a 1,6
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Old 07-29-2007, 07:44 PM   #9
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Originally Posted by emerilnut View Post
the instructions say that there are three ground wires: a system ground (white), a heater ground (blue), and the analog ground (green)

All the grounds need to share ground with the ECU to guarantee zero voltage difference between the two systems (ECU and LC-1), BUT the blue ground needs to separate from the white and green to prevent ground noise.
The LC-1 I got has 3 ground... Black for the calibration that says it should ground to where the Heater (blue) wire goes and the System ground (white). So should I run heater + calibration to the same lug and then into this distribution place and then the white to another lug and a different spot on the distribution place?

I super suck at this wiring thing my brain doesn't comprehend it so well so i ask and ask and ask again before I do anything to make sure I don't fuxz0r it up.
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Old 07-29-2007, 07:46 PM   #10
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Just tap into the GND from the Megasquirt. It'll find it's way.
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Old 07-29-2007, 07:53 PM   #11
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Originally Posted by LunaticDriver View Post
The LC-1 I got has 3 ground... Black for the calibration that says it should ground to where the Heater (blue) wire goes and the System ground (white). So should I run heater + calibration to the same lug and then into this distribution place and then the white to another lug and a different spot on the distribution place?

I super suck at this wiring thing my brain doesn't comprehend it so well so i ask and ask and ask again before I do anything to make sure I don't fuxz0r it up.
Here's what I did. There's a ground (which is supposed to be the ECU ground) located below the throttle body in between the throttle body and the head. You can't miss it. I ran the green and white grounds there.

As for the blue ground and the calibration wire.... I grounded the blue wire to the chassis of the car... I used an unused bolt that was just screwed into the driver side fender well. The calibration wire goes into my car for a push-button switch and LED light. I added a ground wire from there that goes back to the engine bay to another unused bolt on the driver side fender well.

No error codes on the LED yet, so I'm assuming everything's fine. It calibrated just the way the manual said it would.

I hope I didn't screw things up.
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