I need to replace my oxygen sensor on my 89 780. What is the most economical brand/source of O2 sensors available. I really can't spend a lot since I recently had a few expensive repairs done.
Thanks.

As far as brands go, Bosch is typically a bit more expensive, but you can expect a good 5 years (or more) of reliable accurate performance of them, assuming your car is properly tuned and does not have antifreeze or silicone contamiation in the exhaust stream (both of which will kill any O2 sensor). I've tried Walker and Beck Arnley O2 sensors in the past, but they died after about 18 months to 2 years of regular driving (aproximately 15,000 miles). As far as greatest number of miles per dollar of O2 sensor, you can't go wrong with Bosch.

As for using a Bosch O2 sensor intended for the various Ford applications (#13913 & #13953), here's a post with a bit more detail, and part numbers. Be sure to read the entire post and the webpage it points to. Soldering the sensor wires inhibits fresh airflow to the back side of the sensor (since it needs to breath fresh air to make an accurate comparison between the exhaust stream and the outside air).
http://www.brickboard.com/RWD/index.htm?id=713926
3rd part link mentioned in post 713926 regarding replacement Bosch 3-wire sensors

God bless,
Fitz Fitzgerald.
--
'87 Blue 245, NA 230K

on my 90 740 16v I used an O2 sensor off of an 89 5.0 mustang. I had to resplice the connector but other than that I'm happy. It still works fine after 30k or so. The Bosch O2 sensor was $100 or so and the ford O2 sensor which came in a bosh box was $32 I think.

get a good pair of vicegrips and some WD-40

- Nate
--
90 745 16v 175k.

Figure about $40 for a generic/Ford sensor, cut off the connector and splice it into your harness. Some of the generic bosch sensors have a splice kit with butt connectors that you crimp; solder them after you crimp them. I use shrink tubing over the splices and tape the entire mess up.