So now I've reached the point of frustration & need help. I had the engine rebuilt in the burgundy 87 by local machine shop, & now I have a code 13 I can't fix. I've researched all the topics and tracked all the grounds I can withot taking the cradle out. I found 3 & fixed. I also came across a tan/brown wire that was also broke, thought it might be it but it has voltage coming from it (5v, key on) so I taped it off. Checked voltage on O2 & it has voltage. Checked connector & its all the way forward in plug. Is there a place on ECM plug to check if ground is present? Is this D1 on the connector or am I looking in wrong place or wrong tree? I know D7 is O2 input so which is the ground? Car runs great for about 45 minutes before SES light comes on and starts running hot/lean. It is 2.8 auto trans. Thanks!!

D6 is the ground for the O2 sensor... and guess what? It's a tan colored wire. If you've got a multimeter you can double check that the broken wire you taped up is indeed the other end of the wire that leads to D6 by simply unplugging the ECM, placing the meter to read ohms on the lowest scale, then placing one meter lead on the end of the broken wire and the other meter lead in the hole for D6 on the connector. If it's the same wire, then you should get zero ohms, meaning you've got to ground the broken end for your O2 sensor to work. If you don't get any change in the meter reading when you do the test, then that means the broken end is not the other end of D6.

Thanks much Bloozberry!
20 min fix. Can't wait to try it out tomorrow!
Just needed to find another way to attack this and was coming up bricks. Thanks for your time and pointing me in another direction to try!
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Edit: Update. No SES light, but still overheated after 45 mins into drive. Going to look into water pump used and radiator next. Any other directions I might look at?

[This message has been edited by Fishogs 84 (edited 05-05-2014).]