so i have been having this problem show up for a few years now. just living with it. All Digital Cluster
the gas gauge seems fine. the amount of miles traveled seems more or less accurate. estimate fuel economy is 26.3 mpg.
but even that wouldn't account foe over 630 miles distance to empty calculation.
a few weeks ago it was around 350, then 425, in the past it been anywheres around 325 to 555 always after the full tank fuel-up.
does anyone know exactly what is used to make this figure? what are the components involved in making the estimate?
the engine runs fine. i do regular oil changes and replaced air filer a few months back. (had the problem with old air filter too).

 

Let's begin at the beginning --
Air Flow -- New WIX Air Filter -- Clean Mass Air Flow Sensor using CRC MAF Sensor Cleaner -- Clean Throttle Plate and Throttle Body with GUMOUT Carb Cleaner --
Fuel Flow -- Add One (1) 20-Ounce Bottle of Chevron's Techron Complete Fuel System Cleaner -- Replace Fuel Filter with NEW Motorcraft Fuel Filter --
Your fuel tank may have picked up some water over the years, or built up some deposits on the fuel pump mechanism, which would throw off the fuel-level readings.
You list 26.3 as an "estimated" overall fuel economy -- which is very high (good) for a Grand Marquis.
A 20-gallon tank at 26.3 mpgs would yield approximately 525 miles to a full tank.
Real-world fuel mileage on a Grand Marquis is closer to 24 mpgs. -- and that requires everything to be spot-on.
As an outside possibility -- Disconnect the NEGATIVE Battery Terminal -- leave disconnected for 30 minutes -- reconnect NEGATIVE terminal.
You may have just gotten rid of those gremlins ;>
Lemme know how you make out !!

95 MERC Engine Bay

 

Id rather know what exactly is involved in making the calculations. pretty sure its a 16 gal tank.
i have NEVER got anything but around 250 tops or so miles to a tank. hard to say exactly cause i never let it empty out.
my air filter is new. id really rather not go throwing parts on
just to start with a "clean slate" so to speak. like i said in beginning. the engine runs fine.
i might try cleaning the MAF. but thats only reading air flow. is it involved in making the estimate?
has anyone run into this problem before? tied disconnecting the battery in the past and that's never fixed it.
Only other info i can offer is i can see that the distance remaining goes down quicker than real miles. by the time im near empty it will be above the 50mile mark, when i should hear the magic alarm.
\but the Pump on the dash is flashing. which should mean im less that 50 miles to go.

 

Yes, the MAF Sensor measures air flow -- the air flow is part of the fuel-air equation that's giving you trouble. The car's computer adjusts the air flow to the fuel flow as you drive.
I'm sorry -- It appears that you already know what the problem is and how to fix it -- and that my suggestions have no merit.
That's OK, because -- MY Grand Marquis drives perfectly.

'95 MERC at Flaming Gorge, Utah.

 

Your 2000 Grand Marquis has a NINETEEN (19) GALLON fuel tank.
Fuel mileage is quoted as 18 - 23 mpgs.
The famous 95 MERC delivers 16 city, 24 Highway -- just like when it was new -- 170,000 miles ago.

Colorado Rte. 82 - East of Aspen, Colorado -- 12,095' -- Highest Driveable Pass in USA.