If you have fuel dripping underneath your 7.3 liter Powerstroke you just might have a common leak. It starts simply enough, a few drips here and there whenever you park your vehicle, but if it's not taken care of it will eventually lead to pools wherever you go.
The most common place for fuel to leak is from the o-rings on the fuel filter bowl drain valve. This valve is located on the back of the fuel filter housing and the o-rings seem to seal for only a few years before failing. Fortunately this problem is easy to fix.
To verify that you have this problem you can look behind the fuel filter in the valley of the engine. When this leak occurs the valley will fill with fuel, which will then overflow and drip on the ground. The problem with initial identification is that the fuel can run off of the top of the engine almost anywhere depending on how the vehicle is parked.
Leaning over the top of the engine and looking at the back of the fuel filter housing you will see the yellow drain valve. If you lean far enough to be able to see the bottom of the valve assembly, or use a small mirror to look under it, you are likely to see fuel dripping into the valley of the engine.
To fix this you need to replace two o-rings underneath the drain valve. The valve is held on with four bolts with allen heads. Be careful when removing the bolts not to drop them into the valley.
The o-rings should be .5 (1/2)" outside diameter, .25 (1/4)" inside diameter and .125 (1/8)" thickness. The o-rings must be made of viton for wear and chemical resistance. These aren't available from your Ford dealer as a separate part but you shouldn't have much trouble finding them. To get a reasonable price if you order on the internet you are likely to need to buy them in a quantity of 10 to 25 but you should be able to get those for under ten dollars.
With the valve assembly removed you will see the o-rings. They are pressed into place so you will likely have to use something to pry them out. Use a toothpick or other soft material, not a metal tool, as the valve assembly is plastic and scratches can lead to a worse leak than before.
Once the old o-rings are removed simply press the new ones into place with your fingers. Reinstall the valve assembly and the leak should be fixed.
This is the most common source of fuel leaks on this engine. While it is possible for leaks to occur elsewhere be sure to check this area out first. Chances are it will be an easy fix.