I use my Preasure Washer on my engine all the time, never had any problems.
I cover my air intake, and the coil pack, spray is down with a can of Engine Bright when the engine is cool, let it sit for 15 minutes or so, and use the preasure washer on a medium setting, not full blast. Once it's dry I lightly spray the engine with some Meguiar's NXT Generation Protectant, looks great!
I've been doing this on my old '93 Mitsubishi Diamante and on my '98 Taurus at least 3 or 4 times a year. It's never given me a bit of trouble.