I went to put a new O2 sensor on today and the old one had a big copper wire with a red jacket attached to a screw into the chassis. It made it a real chore to even turn the wrench with that dang wire smashed down against the threads.

Why would someone have done this? Some type of bypass on the O2 sensor? It wasn't getting as good of mileage as I thought it should have... 17-19 on long cruising trips and occasionally the check engine light would come on after it hadn't been driven for a couple weeks and needed some carbon burned out of the system.

But why the ugly ground wire attachment??

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(2) 1988 300 SEL W126