if engine is 2.8 or 3.1 its on the back side of engine. The only way to see it is from under the car there's a little 4 inch gap between engine and the exhaust manifold. Its up in there. If engine is bigger its near crank shaft pully and harmonic balancer. you may need to remove them to get at it.
Yes
In the gas tank
Raise the vehicle and locate the speed sensor. Remove the electrical plug. Turn the speed sensor counterclockwise and remove it. Install the new speed sensor.
An 89 Cutlass Ciera holds 7.4 quarts of transmission fluid. When servicing the vehicle, a portion of the fluid remains in the transmission and will not be added back.
This car is fuel injected. There is no carb.
I've got an 89 cutlass ciera and it is located behind glove box. open and pull out like 4 screws and there it is.
Inside the distributor
Possibly an "overcharging" alternator. Check at battery with the eng. running with a DMM.
Does it have enough compression?
Check your crank shaft sensor
The sensor is a "hall effect" sensor, to align it; just match timing marks on cam sprocket to mark on crank sprocket (so they are as close as possible).
I believe that a 89 Cutlass Sl does not have a distributor because of the type of ignition system, the spark and timing are controlled by the the computer if it has one.