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Burning up power ground?

Old 08-07-2013, 04:06 AM
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Default Burning up power ground?

I tore apart my intake manifold and supercharger setup, did some reorg, and put everything back together. The only electrical changes I made during this process were switching injectors from ID725s to ID1000s and moving the ECU ground over one threaded hole in the engine bay, but sanded the **** out of it and the connectors way better than the previous location, and it tests good for resistance to other points in the bay.

When I went to start up the car to make sure everything worked, the car was cranking weakly, which was surprising since I hadn't used much of the battery on anything, and I couldn't get the motor to even pretend to combust anything. Also, after about 15 seconds of trying cranking, I noticed a burning PVC smell and shut everything off. I immediately localized it to the ECU area, where I tore it quickly apart to find a completely burned-to-a-crisp and smoking "power ground" wire (GB12).

I checked impedance on the new ID1000s, which are all 12.2 +/- 0.2 ohms. The old ID725s are all 12.5 +/- 0.2 ohms, so I don't seem to have anything new/bad there. I checked all the wiring that it had touched, and nothing seemed to have melted through other wires, shockingly enough. I ran a new ground to that pin out of thicker gauge wire and tried starting the car again. The car actually jumped right to life this time, but the new wire immediately within a few seconds started getting warm to the touch, so I killed everything.

Any idea what in the holy hell could be going on? :(
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Old 08-07-2013, 04:23 AM
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For reference, I checked all of the other grounds (GB11, BC02, and BC03), and none of them were warm or melted at all. So, something terrible is trying to leave from GB12...
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Old 08-08-2013, 12:28 PM
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Though right off the top of my head- what circuits ground from GB12? Is that even on the injector circuit? It almost sounds like something is crossed up somewhere else. Would it be safe to take a impedance measurement quickly without compromising the wire? I have the wiring stuffs, but it's for 01-03 :( and on top of that, it has Jeremy's revise GB12 ground to chassis, not any indication if that ground was used by the stock ECU before.

Maybe try asking Jeremy/Hydra if GB12 has an OE use?

Kinda related- On my 99, I was changing out a o2 sim for a o2 sensor and I didn't realize the o2 sensor had a bare 12v wire that made ground. Long story short, I cracked open the ECU and found one of the strips had overheated, delaminated from the board and flopped onto a ground circuit causing all kinds of hell.

(side note- hopefully I'll be able to come play with you guys sometime in Seattle)

Last edited by Doppelgänger; 08-08-2013 at 12:47 PM.
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Old 08-08-2013, 01:32 PM
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I figured it out. When I called Jeremy, he called Hydra and asked about GB12. They said that all the grounds are tied together. So, that verified that I wasn't necessarily getting anything through the power inputs, which shifted my thinking.

Checking the car out, I'd neglected to put the ground strap from the head to the body back on when I reassembled the car. Hence, the starter was grounding entirely through the tiny ECU ground lines from the head into the harness, through the tied ground in the ECU, and into the one ground strap I had from the ECU to the chassis. Kinda scary. Really hoping I didn't burn up anything in the ECU, though the car seems to start and idle just fine now that I've rectified that problem (and added additional grounds.)
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Old 08-08-2013, 05:30 PM
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Ouch! Seems like you're rather lucky.
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Old 02-12-2014, 07:57 PM
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Did you have the ground wire that comes from the battery to the powerplant frame near the differential connected? Seems like that would provide eough grownd to the engine without the missing strap...
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Old 02-13-2014, 01:05 AM
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My battery is in the engine bay. The whole wire down the PPF is gone. I had separate grounds that I'd rigged up, that I'd forgotten to reconnect when putting the motor back together. Oops.
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