What causes a blinking check engine light and engine misfire after rain on a Ford Taurus - Mercury Sable?

Answer 1

The keyword in this question is rain...

Water and the engine electrical system just do not 'mix'.

A few pieces of the puzzle to start...

• The flashing check engine light (CEL) indicates the engine computer has detected the engine is misfiring - and lots of it. You should be feeling the engine struggling to run and 'stuttering'.
  
  
• Electrical basics:
• • The coil generates a high-power electric charge
  • The sparkplug wires carries that charge to the sparkplug
    Sidebar: The computer (PCM) times the electrical charge to get to the sparkplug at just the perfect time when the air/fuel in the cylinder is ready to fire
  • The electrical charge enters the sparkplug and ignites the air/fuel into a controlled explosion (of energy).
    
    
• Electricity will take the path-of-least-resistance,especially if there is water/moisture to travel along

To tie it all together...

If there is any weakness or flaw in the connections between the sparkplug wires and the coil, or, at the other end at the sparkplug, the electrical charge is going to escape, or take a detour and not make it all the way sparkplug!

So in this case, focus your efforts on finding where the electric charge / 'spark' is escaping:

• Replace sparkplug wires - chances are yours are original and about 10 years old. They've done their job and time to retire them.
  
  Might as well do the sparkplugs while you're in there.
  
  
• Inspect the coil for any signs of cracks or breaks / flaws in the surface.
  
  Electricity often leaves a light gray-colored track on the surface of the coil - a good indicator of leaking at the wire/coil connection point.
  

In my immediate case, I replaced the plugs and wires, but the misfire/hesitation problem did not go away - it was better, but still bad especially in wet weather. Tomorrow I replace the coil.

See "Related Questions" below for very detailed instructions/information on replacing plugs, wires, coil and firing orders and more.