Depending on whether you have the v6 or 4 cylinder:
V6 - Right up front behind the radiator. Slide under the vehicle about a foot and a half or two feet at the dead center from the front bumper. Then look about 1 foot to your right and you should see it.
4 cyl - I don't have this vehicle but the manual states it "is at the back of the engine, it is impossible to reach it from above. It is almost as impossible to reach it from below. It may be easiest to remove the right front wheel and reach through the fender opening to get at it."
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The oxygen sensor on a 1989 Chevy Celebrity is located in the rear exhaust manifold on top about the center.
The thermostat on a 1989 Chevy Celebrity is located under the water outlet fitting. Follow the upper radiator hose, it will end at the water outlet.
The petcock on a 1989 Chevy Celebrity is at the bottom of the radiator on the drivers side.
in the fuel tank
On all models of Chevrolet Celebrity with fuel injection the fuel pump is inside the fuel tank.
The computer is mounted to the firewall on the inside of the car behind the globe box.
It is behind a cover on the driver side strut tower.
It is located on the driver side. Right below the second door.
It sounds like your engine is not getting enough fuel, try checking the fuel filter.
There is no cabin filter on a 1989 Chevy Silverado.
Looking in my factory service manual for a 1989 Chevy Celebrity I found no reference to an accessory relay.
The spark plug gap for your 1989 Chevy Celebrity 2.8 V6 is .045".