one day my 03 grand marquis ran just fine next wont start ? runs on starting fluid

Clean throttle with spray throttle cleaner add Lucas Fuel Injector cleaner to gas tank.

Evidently if it runs on starting fluid and stops when starting fluid is gone, it is not getting fuel to the engine or the injectors are not operating. Bad fuel pump, bad fuel pump module, engaged inertia safety switch, bad ECU or bad fuel pump wiring are all possible causes.

replaced the fuel pump relay first. Also, a scan reading might show if that's it, or the things mentioned above.