Don't pressure wash the top end of the motor or the electrics--not a good idea. I have used engine cleaner/degreaser, but like Cozy said, Simple Green works pretty well too. If the engine is caked with gunk or old crusty dirt mixed with oil and grease, you can use oven cleaner on the steel areas of the motor, but understand you may hurt the painted parts. I used oven cleaner on the used V8 I bought from GM Sports Salvage, just to clean off the 10 year old crud. After spraying and soaking over 3 mil plastic sheeting, I used a putty knife to scrape it all off and then bundled up the mess and tossed it. After that, I used Simple Green to get rid of the rest and then wiped it all down with 3M product before shooting with new paint.
Hopefully you just have a little dirt that can be pressure washed off.
Davy