I found a real nice suprise when doing the header.
The O2 harness runs up past the oil pan then gets held to the block with a loose clamp.
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Look at what engine heat did to the wire inside that clamp.
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That explains a lot as to why the sensor checked out ok (from the sensor connection) but still wasn't reading right on the DRB.Wire and solder should fix this but I've got to find a better route for that wire.