2003 Mercury Optimax 225 hp. BEEPING than constant buzz behind gauges after starting and running from winter layup. Put all fuel additive and topped oil injection reservoir.

Question edited for clarity, make and model names (it is written all over the vehicle :>).
Question moved to sub category.

For strangeness like that, it is best to take the car to an auto-electrician with a pro grade scan tool. It is a known issue if you want to try and fix it yourself. Watch all the videos, but they deal with gauge problems, not the beeping. Partway down says it is caused by an evap hose leak.

https://www.google.com/search?q=2002+Mercury+Grand+Marquis+LS+Beeps+fuel+gauge+rises+with+each+beep

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ambient air temp or BARO sensor failure that is not telling the ECM to enrich the fuel mixture
run the fault codes

check and test fuel pump

Try new plugs

could be several things , Check fuel pressure and flow, if flow is low replace fuel filter, if pressure is low check fuel regulator, if ok replace fuel pump. Check throttle position switch for smooth movement . A misfiring coil or spark plug HT cables can also cause this fault.

it appears to be a fuel starvationproblem
it can be from the tank vent still locked close
fule lines collapsing internally
fuel pump diaphragm fai;lure
blockage in the main jets
even tye hand pump bulge in the line can be failing and blocking the fuel lines

start by going over ignition system and fuel

Gauge fuse runs a fuel module that is installed to correct vapor lock. This module is what is running the pump. This module, called the hot fuel module is mounted on the passenger side behind the dash above the blower motor.

Here's a step by step, with photos, on how to replace an Explorer fuel filter. The Mountaineer should be exactly the same. The problem you describe can be attributed to the fuel filter. Good luck.

Mercury Mountaineer fuel filter is located in front and on top of fuel tank behind two shields. . When you look just behind the front passenger side tire you will see the first shield. Behind that is the second. U will need to buy the fuel line release tools to get the lines off the filter, any good auto parts store will have these.