What the title says. I have an '86 base model Firebird with the original 2.8l v6 in it. This issue has been going on for about a month or two and I thought it could have been an issue with the sensor, but I replaced that today and it's still doing the same thing. Pressure starts out fine, in the 40-50 range but slowly drops down to about 10 lbs when the engine warms up to temp, and it starts idling low too. Also, there's a small amount of oil leaking from the pan, I'm assuming that's the just the gasket because it hasn't been replaced in 40 years. Anyway, I'm thinking this could be a failing oil pump, but I want to hear everyone's thoughts here. I can provide more info if needed.

 

Probably a worn oil pump-aluminum pump body on 60*v6 -shaft hole wears and lets pump gears rub housing and wear too much clearance