RustX7

So I'm trying to diagnose my idle bouncing between 1300-1600 in my 87 TII and I decide to check my ECU grounds. Fine.

Three of the four appear to be fine - pins 3G, 3A, and 2R. I check them with an ohmmeter and their resistance to ground is quite low, 0.2ish ohms (some of which may have been coming from a wire I was using to extend a known good ground to where I was working in there by the ECU.) Not perfect but at least there. Great.

The fourth, pin 2C, is not grounded. It's just, nothing. No response from the ohmmeter between it and ground.

At this point I notice that the wire going into that pin is not black. The one below it, however, is black. That one is pin 2D, which is for the O2 sensor. So I'm like, "Hmm," and I go into the engine bay and unhook the O2 sensor (the connector for which could stand to be in better shape) and check for continuity between the engine bay connector and the ECU connector. There isn't any.

At this point I get all excited because I think I've discovered that the jackass who worked on the ECU last decided he'd swap the ground 2C pin with the O2 sensor 2D pin. No such luck. I check 2D and it isn't a ground either.

Here's where it gets even more fucked up: The O2 sensor connector in the engine bay appears to be shorted to ground. Shouldn't it just be a dead, open circuit if I've unplugged it at the ECU?

To get even more fucked up:

I go look at my friend's N/A parts car ECU and his 2C wire out of his ECU goes and crimps to the 3G node and what I guess is the ground sheath around his O2 sensor line. That all makes sense to me. My 2C line, on the other hand, doesn't connect to any of the other grounds. It's a brownish wire that leads up into the rest of the harness, going to god knows where.

What the **** happened to my harness? Why isn't it normal?

BTW my O2 line going into the ECU at 2D appears to be coming from the right place - the grey wire with the ground sheath. Problem there is that wire doesn't go to the O2 sensor because the O2 sensor is shorted to ground somewhere. I'm guessing wherever that sheath starts there may be some abrasion that made it short but I dunno yet.

As for what the hell's hooking up to my 2C pin instead, I have no clue.

I don't know if anyone followed this, but I'm open to ideas if anyone did... thanks

RustX7

OK scratch one of those statements, I know someone probably worked on these pinouts, that's why it isn't normal. So there's a chance I'm not smoking crack when I think this thing is fucked up.