does any body know what this is and what it does
It's an 02 sensor. it measures the oxygen content of your exhaust for the ECU to adjust fuel trim among other things.
This image is an 02 sensor listed as for a 1984 to 1987 Buick G/N Granted, it's not identical but that is an 02 sensor you have there
It looks like the old noise suppressors that they put on the coil of the ignition system, however your is broken, the mounting tab is missing that is what the two little holes are in the body of the condenser. If you don't get any radio noise from your ignition when it is running then you don't need it.
it does not look like a o2 sensor.. could be a knock sensor.
OK I'm convinced, You guys payed more attention I should have enlarged the picture.
Looking for a Used Grand National in your area?
CarGurus has 1 nationwide Grand National listings and the tools to find you a great deal.
Search Buick Grand National Questions
Buick Grand National Experts
Related Models For Sale
Used Cars For Sale