I don't see why an engine ever needs to be pressure washed. If it got mud splashed on it, then a garden hose should suffice. Otherwise you're more LIKELY(not necessarily) gonna cause an issue. High pressure, cold water is one of the least efficient ways to clean up oil based soils(think about doing the dishes).
So you're better off going at it carefully and thoroughly, or not doing it at all which I honestly think is fine too, engine bays aren't supposed to be clean. plus, Why would anyone want to remove the lovely corrosion protective film!
I clean less often and take a more methodical approach. I target each part individually. I start with a plastic bag over distributor and hose any mud, leaves, etc off with a low pressure garden hose, avoiding the valve cover and throttle body areas.
-Timing cover area can't even be seen so I don't bother cleaning down there.
-Distributor gets cleaned with naptha soaked towel, same with valve cover, intake manifold, throttle body, and head. In other words, aluminum parts get solvent based cleansers.
-Air box, hoses, plastic covers(not the fuse box cover), fender surfaces, hood seals get wiped with water based degreaser(simple green, zep industrial purple) on a rag or sprayed and agitated. then thoroughly rinsed. Sometimes a final wipe if I care about water spots.
-Wire harness and connectors especially get a wipe with a mild cleaner on a towel and then another wipe with a damp paper towel, if anything at all. most of the time it's not even worth trying to get them spotless. I'll rewrap with high temp electrical tape if it really bothers me.
What was the issue with the simple green?
It's an alkaline cleaner, can and will attack aluminum if not completely rinsed off or left on for too long.