It's in the tank.
For a 1991 Mercury Grand Marquis : " regular " unleaded gasoline , 87 octane is used for both the 5.0 and 5.8
the fuse box on a 1991 ford grand marquis is located right under the steering wheel
Who told you that you cannot install any 5.0? Of course you can with the proper modifications.
Why cant you put any 5.0 engine in your 1991 mercury grand marquis
its in the trunk
As far as I know , the 1991 Mercury Grand Marquis either had the 5.0 litre / 302 cubic inch V8 or the 5.8 litre / 351 cubic inch V8 engine . The 4.6 litre Single Over Head Cam ( SOHC ) engine was used in the Mercury Grand Marquis starting with the 1992 model year Firing order of the 5.0L which is the engine installed in the 1991 Mercury Grand Marquis is 1-5-4-2-6-3-7-8 rotor turns counterclockwise.
If your Mercury Grand Marquis is a 1991 model or older . The 5.0 liter / 302 and the 5.8 liter / 351 has the distributor at the front of the engine The distributor rotor turns COUNTERCLOCKWISE
Heater core leaking.
Try adjusting the modulator valve
According to my Chilton's Auto Repair Manual : For a 1991 Mercury Grand Marquis : Both the 5.0 liter / 302 and the 5.8 liter / 351 take : 4.0 U.S. quarts without filter 5.0 quarts with engine oil filter change
No,they won't fit.