If you use the "search" function here, you'll find lots of advice - and lots of war stories. Personally, I've pretty well given up on doing any serious cleaning under the hood of my Ford trucks - and I absolutley refuse to do anything with customer vehicles. Why? Because there are more things you can do wrong that you can do right. And, most of the things you can do wrong will end up costing you money.
Somewhere back in the forum archives is a post from me about cleaning the engine compartment on my 2002 F-150 just before trading it in. After all, doesn't a well detailed vehicle bring you more in resale value. ( Yes, if it's running.) As carful as I was, I wiped out several coil packs. When talking to my dealer about it, he told me he recently fired a detailing guy because he'd caused so many under the hood problems on cars he detailed.
So, if you follw JGG's advice, you'll maximize your chances of success. However, I did virtually the exact same thing and it end up costing me several hundred dollars in repairs. You'll find some folks here will claim to have blasted away with pressure washers and never had a problem. To that I ask you, "So, do you feel lucky today?"