On my 1994 Bravada the oil filter is located behind the driver side headlight, if the 1991 has an oil cooler like the 94 it is probably there also. You might also ask at this forum I have found useful http://www.gminsidenews.com/forums
on the turn signal switch
4.5 to 4.75qts
Behind the driver, under the frame.
1991 to 1994, then again in 1996 to 2004.
A 1991 Olds Bravada has a curb weight of Curb weight: 3939 lbs. Factory options included towing package and a digital dash.
Usually the fuel filter is located towards the middle to the rear on the drivers side attached to the frame.
It is located by the rear axle behind the fuel tank.
Pump is in the tank, the filter can be found by follwing the fuel lines fromt the tank forward.
In the tank
I know the fuek filter on a 1992 88 is in the fuel line under the seating area. Be careful not to break the plastic "quick-connect" fittings.
full filter locatoin on a 1991 Cadillac Seville