20 Most Recent 1991 Mercury Grand Marquis Questions & Answers

Question edited for a lot of clarity. Question moved from MISC to correct category. https://www.google.com/search?q=1991+Mercury+Grand+Marquis+GS+5.0.+Vacuum+hose+diagram&rlz=1C1QJDB_enCA643CA644&sxsrf=ALiCzsbNrlH1W5VV0OAK4h8jTsQrUJYYeQ:1662518015156&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjzjued0oH6AhWShYkEHWqvAisQ_AUoAXoECAEQAw&biw=1920&bih=937&dpr=1 ..

This may be one of those where the entire dash has to come out to do the heater core. But you only want to replace the core if it is plugged, or leaking. There is an easy way to tell if it is plugged: with the engine at normal operating temperature, and the control valve open so coolant will circulate, now feel both heater hoses. If core is blocked, only one hose will be hot. If core is circulating correctly, both hoses will be hot. If they are, you don't need to change out the core. One of your vacuum actuated doors is the problem, the blend door that lets air from the blower motor pass over and around the heater core.

It may have jumped time. However, if you smell gasoline, it got flooded. Here is the lay of the land.
If it cranks, as in turning over but not starting. And you smell gasoline. The fuel is good, but there is not electrical spark going to the plugs. Bad coil. Cracked distributor cap. Moisture under the cap. Check this before you worry about the timing. You first have to test for ignition. Also don't pump the gas when starting it. See what happens. Also when the car is warm, never pump the gas. Also check the wire going from the distributor cap to the coil.
Good luck,
Hope this helps,
Best,
Mark

Sorry, this is confusing, can you not just lock/unlock with key without disabling central locking?. Please add more detail

check the fuel filter

Could be a problem with the key lock cylinder. You could disconnect the shift cable and try shifting the lever on the transmission. That would tell you if it is a shift lever problem or something inside the trans.

disconnect the battery for a day and see if the computer resets.youre local ford dealer can help you if that dont work

Bad battery...can't be charged

4.6L engines are electronically timed. You cannot change the timing. The only thing that can be done is line up the head/valves and piston rotation.

If your car has one installed already, the plug will be coming out of the grill in the front of the car or hanging down just inside the grill. If you need to purchase and install one, they are for sale at most online automotive retailers and many Auto Zone and O'Reilly's

look in the trunk for an inertia switch, usual on the d side. also called a crash switch. sometimes a fuel pump problem will trip this switch

Could be fuel problem, electrical problem or cooling system problem. 1st thing you should do is get the trouble code from the computer. Most Auto Parts stores can retrieve the code for you. Troubleshooting is easier with a direction to go in.

Someone will need to figure out if you are loosing spark to the plugs or fuel pressure when it fails to start.

Really? Go on Google, and type "1991 Mercury Grand Marquis Fuel System Diagram." Dozens of them some up. (Helps if you know how to spell the model name of your car. When in doubt, it says on the car, in several places, and in big letters.)

Becomes very noisey or leaks fluid or steering gets notchy or stiff to turn as pump not making enougth pressure