What kind do you use? Also do you have to cover anything up so it doesnt get damaged? Im looking to try and clean mine up a little, nothing too crazy. Thanks

Simple Green now has a new bottle out thats a bit more diluted or you can buy the regular stuff and mix it 50/50 with tap water and spray down the engine bay. I would take some tin foil and wrap your PCM, remove engine half covers and take a trash bag or wal-mart sack and wrap your air intake filter so it does not get wet. Spray down the entire engine bay and using a tooth brush or cloth clean the dirty areas. Do not let it dry and wash off immediately. Remove tin foil from PCM and plastic from air intake filter and go for about a 20 minute drive come back and pop the hood and use compressed air or a towel to dry areas.

When its all dry you can go by most automotive parts store and buy some CD2 Engine detailer its like armour all for the engine bay give it a nice shine and all you have to do is spray it on and walk away.

This is a great video
http://www.youtube.com/watch?v=0_AmiVp8Ni8

I use Black Magic 2 in 1 engine cleaner. I don't cover anything..... but that's just me. I've been doing it for 2 years now. Spray the whole can over everything, let it sit for 15 mins., hit it with some good water. Wipe and dry everything down, then I spray the whole compartment down with some Armour All Natural Finish and let it sit for a few then just wipe off the excess. It comes out pretty good.

http://i609.photobucket.com/albums/tt173/HarrisonZ/DSC07228.jpg

If things aren't really greasy under the hood you'd be surprised how much you can clean with just high pressure soap and water at a self-serve car wash. My wife's Explorer gets washed less in two years than my truck does in a month, but the method above was enough to get it spotless the one time I cleaned under the hood. Just spray the soap, wipe everything with a brush, rinse, let it partially air dry while you clean the rest of the truck, then go back and dry off any remaining water.

Simple green, a garden hose, and a variety of brushes work. The nice thing about simple green is it is biodegradable and won't damage paint. Obviously cover the air filter, especially if you have an intake with an open element. Avoid areas like the computer. You can cover them with a plastic shopping bag. The electrical connectors in modern cars are sealed to prevent water from getting in, so techinicallyt the entirer engine bay should be able to get wet. Water splashes up when driving in the rain anyway. I like to run the engine and use a leaf blower to dry things off quickly. Or if you want to do it quickly, find one of those self car wash places with the stalls you drive into. Most have an engine cleaner setting. Ideally you want to park the car/truck and let it sit with the hood open and engine off for a bit to cool off. I wet down the entire engine bay and apply the engine cleaner. Avoid the areas mentioned above. I also like to use the brush with the foam soap to scub the engine bay. Rinse everything well to get the soap off. Don't spray high pressure water at any of the electrical components or at the connections. Start the cat/truck and go for a drive so it dries off. Some people might be wary of this method but I have never had a problem. I spilled some atf when doing my trans service the other day so I actually cleaned mine this way today.

I get the best results with what I have been using for years. I use a can of airosol "GUNK" Engine 2 in 1 cleaner/detailer. (can find at any local auto parts store and even most supermarkets). Start off with a totally cold and dry motor. Spray entire engine bay with engine off (I dont cover anything any have never had any issues thus far). Let sit for atleast 15 minutes. After 15 minutes start engine and hose everything off. After all cleaner is hosed off wipe down with towel. Fast, easy and comes out looking professionally detailed.