99 grand marqui wont start but turns over

Check your fuel pump relay, check fuel pressure with a gauge. Those relays go bad. Pump could be bad, do you hear it hum? Also, there's an inertial cut-off in the trunk that can be reset after a wreck.

I'm having the same issue. The pump does hum. Is that my issue? Replaced the battery, starter, and throttle body cleaned with a new throttle position switch. Was going to replace the fuel injector sensor and neural safety switch next. It starts when it wants too.