My 2001 Grand marquis oil gauge it below red and running roughe

Hook up a mechanical oil pressure gauge for testing purposes and see what the oil pressure really is. If it's really that low and this is a higher mileage vehicle I'd suspect worn bearings in the engine. If the oil pressure is actually good, check the wiring going to the oil pressure sending unit. You might have a bad connection. As for the rough running, is the check engine light on? If so visit your local auto parts store and have them scan the computer for trouble codes. Once you get the codes we can help further! Hope that helps! Jim

If you put in a new oil pump and oil pressure sender and you still have low oil pressure then a manual gauge temporarily installed will tell you if you have worn out engine bearings. If you do then it time for either a complete engine overhaul, engine replacement or scrap it.