how often does my 2005 mercury grand marquis with 57,000 miles need a fuel system tune up?
Never, if you’re referring to a fuel system flush, unless you notice it running rough. A common ‘upsell’ item for shops.
Unless there’s a drivabilty issue, the fuel system doesn’t need a tune-up. Whatever that entails.
He might be leaning towards “Techron”
The only thing to do regularly is replace the fuel filter. Check your maintenance schedule for frequency. Mine doesn’t actually say anything about it even though its a standard inline fuel filter. But I change it on a rough 2 yr/24K miles schedule.
Check the maintenance schedule that came with the car. You won’t find “fuel system tune up” because it’s not necessary. Ever.
This is what’s known as a “profit generator” for car dealers and unscrupulous mechanics.
Drive on and save your money.
Like almost all maintenance items, all you need do is to follow the schedule in the owner's manual. Other than the fuel filter, there is nothing you need do. However if you feel you must there are lots and lots of products out there you can spend your money on, and the best part is they are not likely to do any damage. In a rare case, they may give some advantage.