1997 Buick Century car will not start but once a day

When you say the vehicle (won't turn over) that means it won't crank. If the starter won't crank the engine, you got a problem with the starter circuit.

If the vehicle cranks good, but won't start, that is another issue. If it cranks good, but won't start, have a helper crank it, while you check for spark at the plugs. If have spark everywhere, you might try spraying a little carb cleaner or something in the throttle-body, I usuall take the air-duct loose from the throttle-body, open the throttle valve, spray a little in there, see if the engine will try to start, if it does, sounds like a fuel issue. Whether that is caused by no injector pulse or low fuel pressure, whatever.

Are there any troublecodes? Some of the national brand autostores will check codes for free. I guess if you kill it at the store, you may not get it started again. Maybe you'll get lucky?

Also check ALL the fuel injectors for a shorted injector, I just got done fighting with one with two bad injectors that had me pulling my hair out. I believe the correct resistance is about 3 ohms. Hope this helps.

I had two bad fuel pumps too, one would run but would not make pressure. Quality control at it's finest!

If the (fuel too rich) code is current, it may not be the pump? You might have a ruptured diaphram in the pressure regulator, that might allow gas to be sucked or drained into the intake. If you pull off the vacuum line, does gas run out?