2003 Mercury Mountaineer will turn over but won't start, what can it be?

SOURCE: 2003 Mercury Mountaineer no heat

no you have to remove the vent between the hood and the windsheild its on the out side of the car it sounds like your freshair vent is stuck open

SOURCE: cabin filter location mercury mountaineer

There is one for the 2003 Mercury Mountaineer. If you are smellign a "vinegar" odor, mix a solution of 1 part bleach to 3 parts water and pour it down the grid at the base of the windshield. It will take care of the smell.

SOURCE: how do you change the spark plugs on a 2003

1. Most of the 4.6 Litre engines have some form of plastic cover, mine was held in place with two 11mm nuts at the front and press-fit connection at the back. Remove this cover to gain access to the spark plugs. You may need to disconnect the air hose going to the throttle body and some additional vacuum hose connections. Mark them with masking tape and numbers if you have any question about re-attaching them correctly. Along each side of the intake manifold you will see 4 round coils held in place with a 7mm bolt on each one. Remove the 7mm bolts from each coil. Each of these coils has a connector that will be disconnected by pinching the connector to release the catch and pulling gently. Do not worry about marking them unless the wire harness has been modified. The factory wire harness keeps the connectors next to the correct coil.
   
2. Remove each coil and plug connector by gently turning the unit to break the rubber loose from the manifold, then pulling up on the coil/plug connector as a unit. Do not be alarmed if the rubber boot cover comes off, you can easily reattach it to the coil. Once the coils and rubber boots are removed, use your compressed air source or vacuum to remove as much debris from around the spark plugs as possible. Warning: Wear Eye Protection when using compressed air.
   
3. Remove the spark plugs using the 5/8" spark plug socket, swivel, extension and ratchet. Some engine installations may require additional extensions or swivels to get the back plugs removed. It normally takes just an 1/8 turn to break the plugs loose and then about 4-6 full turns to fully remove the spark plugs. If the plug does not come out with the socket, use the magnetic pickup tool to pull the plug out. You will not be able to reach it with your fingers.
   
4. Using the feeler gauges gap your new spark plugs to the correct gap for your vehicle. A typical spark plug gap for this engine is .054 inch. With the plugs gapped, fit the rubber fuel line to the top of a spark plug and then apply a small dab of anti-seize compound to the plug threads. Work the anti-seize into the threads a little bit and then insert the plug into the engine. The rubber fuel line will prevent you from cross-threading the spark plug and you should be able to turn the plug in about 3/4 turn or more easily. If not, remove the plug and make sure that it has not picked up any debris in the threads. If so, clear it out and try again. Once you have all of the plugs started, use the 5/8" socket to tighten them just 1/8 turn past their stopping point. Do not over tighten as this is the leading cause for plug-blowout with this engine series.
   
5. With all of the spark plugs back in, you can then proceed to replace the coil/plug connectors. Replace the 7mm bolts for each coil and tighten them snugly but do not over tighten. With the bolts tight, the coil/plug connector should still rotate slightly. Reconnect the electrical connectors for each coil by gently pushing them in place until they click. They are indexed and will fit only in one direction.
   Reconnect the air hose to the throttle body and any vacuum lines that were removed. Replace the plastic engine cover and fasten it in place. That's it, your done.
   

SOURCE: 2004 mercury mountaineer wont start will turn over not crank

the igintion switch is bad

SOURCE: Heat does not work, makes loud clicking noise when

I have a 2003 Mountaineer that had the same symptoms. After doing some research, me and Google decided it was the Blend Door Actuator. It is a fairly difficult job due to having to take pretty much the whole dash off, but I did it myself with minimal experience. I included a few links.

http://redhouseon7th.com/redhouse/howto/2003FordExplorerBlendDoor/ (This is the guide I used.)

http://www.explorerforum.com/forums/showthread.php?t=212667

Good luck!