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Old 09-09-2012, 07:09 PM   #1
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Default ECU burnt out. help!

Well thank gosh my car atleast made it to the stop sign about 40 yards away before i noticed anything. It was driving fine and then at the stop sign I hit the gas and let the clutch out to pull foward. I didnt go anywhere. Thought i stalled like a noob well tried it again and i noticed smoke coming from the ecu area.GD

The actual harness wires and plugs dont seem to have any damage, just the left side of the big plug(connector) for a 96 miata. I believe the wires are both black with a light green stripe but they are at least black and on the very left side.

So my question's are exactly:
1. What are these wires for, I've looked around and can only find circuit diagrams.
2. Will maybe a wrong wired o2 sensor cause this? I had to splice a post cat o2 in to a pre-cat connector, so i didnt actually splice the engine harness.

Yes i will be buying a new ecu i just do not want this to happen again.
Thanks.

Oh and obviously in the pictures the ecu is upside down so it would be on the left side of connecter!


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ECU burnt out. help!-mms_picture_2-2.jpg   ECU burnt out. help!-mms_picture-2.jpg  

Last edited by KsoV; 09-09-2012 at 08:15 PM.
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Old 09-09-2012, 07:51 PM   #2
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For ref...

black/light green is sensor ground
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Old 09-09-2012, 08:14 PM   #3
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Ahhh thank you so much, I must be horrible at googling because that excactly what i was looking for.

And for more newbness exactly what does it mean by sensor ground? All sensors?
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Old 09-09-2012, 08:44 PM   #4
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I believe so.

FYI I found that info in this thread:
https://www.miataturbo.net/useful-sa...asquirt-13676/
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Old 09-10-2012, 09:51 AM   #5
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the wire that burnt was your 12v wire on 4B, not the grounds. Something is shorting your 12v to ground, probably in cabin. When that happened, the wire got super hot (think hair dryer heating coil) and the weakest link is the PCB and copper traces, which started melting/burning first.


You probably want to go back and wire the o2 correctly. Why not post up here EXACTLY (to the freaking T) how you wired it, and we can tell you how to fix it.

It's highly possible the ECU is still perfectly fine.
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Old 09-10-2012, 10:35 AM   #6
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Well its the post cat o2 sensor from Rspeed(ordered the wrong damn one) So instead of me cutting the actual main harness I took the old o2 and snipped off the clip and wired those together since they were the same color wiring. So i honestly have no clue maybe a wire somehow touched another one but i wired them really tight with alot of tape.
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Old 09-10-2012, 10:40 AM   #7
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Hmmm also i did the nrg short hub mod where you have to cut the airbag wires, could that short it with out a resistor or something since you said cabin?
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Old 09-10-2012, 10:47 AM   #8
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Quote:
Originally Posted by KsoV View Post
Well its the post cat o2 sensor from Rspeed(ordered the wrong damn one) So instead of me cutting the actual main harness I took the old o2 and snipped off the clip and wired those together since they were the same color wiring. So i honestly have no clue maybe a wire somehow touched another one but i wired them really tight with alot of tape.
This is probably an issue. but youre saying the 4 sensor wires were exactly the same colors?
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Old 09-10-2012, 12:06 PM   #9
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My guess is you had a power filter capacitor in the ECU fail, turn into a dead short, and cook the board. That happened on a Honda I used to have (probably the third worst lemon I've ever owned, behind a junk Capri I only bought for the body shell and a Triumph Spitfire with burn marks all over the wiring harness).
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Old 09-10-2012, 02:46 PM   #10
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Quote:
Originally Posted by Braineack View Post
This is probably an issue. but youre saying the 4 sensor wires were exactly the same colors?
yes, exactly the same but the connecters were different so that was the only reason I had to splice.
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Old 09-10-2012, 02:52 PM   #11
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Also i picked up a bp3a ecu from the junkyard just in case, just need a o2 sensor now.
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Old 09-10-2012, 08:33 PM   #12
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Hmm put in the ecu and o2 sensor, it cranks and fires but then wont idle and nothing when I press the gas pedal.
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Old 09-10-2012, 08:43 PM   #13
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Quote:
Originally Posted by Matt Cramer View Post
a Triumph Spitfire with burn marks all over the wiring harness).
Those were OEM burn marks if your Spitfire is wired anything like my TR6. The "fuse block" in that car has positions for 4 fuses, but the factory only populated 3 of them...

KsoV: So, you are not using any part of your homebrew O2 sensor harness now?
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Old 09-10-2012, 08:47 PM   #14
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Quote:
Originally Posted by EO2K View Post
Those were OEM burn marks if your Spitfire is wired anything like my TR6. The "fuse block" in that car has positions for 4 fuses, but the factory only populated 3 of them...

KsoV: So, you are not using any part of your homebrew O2 sensor harness now?
Nope, no homebrew now. Trying to do some research but every thing i find states they are interchangeable. I did get it from a junk yard but looks to be in great shape so who knows, maybe its a dud from sitting so long in FL weather..
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Old 09-10-2012, 08:50 PM   #15
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The car is a 96? Is that OBDII? I can never remember. I'm wondering if its throwing a code at this point with the new ECU?
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Old 09-10-2012, 09:34 PM   #16
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Quote:
Originally Posted by EO2K View Post
The car is a 96? Is that OBDII? I can never remember. I'm wondering if its throwing a code at this point with the new ECU?
Yes to both of those questions. Well my research says that it will run and drive identical but the check engine light will always be on, so before i go and buy the used correct ecu for the 96 i will have a buddy come by with a scanner.

thanks for all the help buds

p.s The old ecu is completely shot as i plugged it back in and in return got nothing.
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Old 09-11-2012, 10:24 AM   #17
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Quote:
Originally Posted by EO2K View Post
Those were OEM burn marks if your Spitfire is wired anything like my TR6. The "fuse block" in that car has positions for 4 fuses, but the factory only populated 3 of them...
Yes, my Spitfire had only three fuses and no circuit breakers. Not a single one of them was on the headlight circuit. And the headlight wires rub against the edge of the hood when you open it...
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Old 09-11-2012, 03:45 PM   #18
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Hey Matt, ever see anyone get cam and crank signals off a 2.5l Triumph 6cyl? I'm open to ideas as I'd love to have an MS built to run sequential injection/wasted spark on this beast, you guys do much custom work?

Sorry KsoV, I'll try not to be too much of a distraction here
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Old 09-11-2012, 04:24 PM   #19
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Ha no problem guys,trying to get a scanner by tomorrow night
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Old 09-11-2012, 05:52 PM   #20
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Hmmm I didnt get a scanner yet but i remembered that one day it seemed like my MAF went out then i recent my old ecu. Then it worked until the old ecu did its thing. So possibly a bad MAF that cause it?
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