'91 3.1 : My oil pressure guage is wacked and I'm guessing the oil pressure sending unit is bad/dirty/broke. Where is it located? Beside the oil filter?

How hard is it to change? What should I expect to pay for a new one?

yup, its right by the oil filter. very easy to replace.when my gauge didn't work i didn't know if it was the sensor or the connector(mine was cracked) so i replaced both. the sensor was $25. just disconnect it, unscrew, replace.
you'll need a rather large wrench though, maybe a 22mm....or a big crecent wrench.

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Dan
1990 3.1L RS
80 Series Flowmaster
It's fast(er than a 3 cyl metro)

You have a gauge.
It's the large cylinder connected to the oil filter housing. You MAY be able to remove it with a 10mm wrench. One wire to it!
The light sensor is a 26mm socket. I discovered that as I need to swap my light sensor for the guage sensor. I'm using the old one from my S-10 Blazer, it's identical to new one

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Chat Soon,
KED85
Karl
1985 Firebird 2.8 to 3.4 swap project for Smog Happy LA, CA

Thanks for the info.

... so that I don't get ripped off, about how much is a new one?

Dan gave the price & he's correct. That's why I'm taking my old oil gauge pressure sensor off my 1985 S-10 Blazer. It still works, after 211,500 miles. Why waste $25?

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Chat Soon,
KED85
Karl
1985 Firebird 2.8 to 3.4 swap project for Smog Happy LA, CA

$25 is the kragen price. if you go to the dealer expect to pay WAY more.

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Dan
1990 3.1L RS
80 Series Flowmaster
It's fast(er than a 3 cyl metro)

Thanks.

(... sorry I should have paid more attention when I read the previous posts.)