LOL, I had to have my throttle body replaced after I gently washed my engine. It was just out of warranty but the dealer covered it. I know the mechanic there personally and he said it was just coincidence, but I find it hard to believe that I didn't some how muck up the electronics, which sent some bad signals to the computer controlled throttle body. Who knows.
Even though my mechanic friend says that the electronics/computers are well protected from moisture, I would cover an accessible parts with plastic bags: the pcm that sits on top of the air filter, especially the fuse box and the TIPM that sits below it ("looks" vulnerable from the underside view).
I would use a very gentle stream from above only. Be careful using high pressure from below, especially around the TIPM unit. Have the engine warm (not hot) so that moisture evaporates off quickly. These are just my opinions.
For a cleaner, I like to use Simple Green Pro HD formula from Home Depot. Per their website and personal comminication, I learned that it is the homeowner version of their aviation product that is designed to be safe on aluminum, rubber, plastic, and most materials sensitive to chemical corrosion.
when cleaning engine bay
I warm up the engine to just warm, not hot
I will spray on a degreaser on metal parts, making sure not to get it on soft parts like hoses/belts,
let it soak
I scrub/wipe as much as I can
I then cover electrical connections and sensors with whatever plastic bags I could and power wash it down,
then run the engine to dry it up
Wet the paint(fenders, grille, hood, bumper) 1st! Then spray any degreaser like LA's totally awesome, simple green, 409, purple power etc... onto the engine and under side of hood liberally. I usually scrub the underside of the hood and any painted areas I can get too with a wash mitt. Use a hose, not a pressure washer in my opinion and rinse. Should come out great! If you want it to shine apply tire shine spray, or any spray that is silicone based that is designed to shine plastic and rubber but just realize these sprays will attract and allow dust to cling to it so the engine will need to be redone on a normal basis.
Don’t pressure wash it. Take it apart as much as you can and use paper towels and spray cleaner or degreaser. You can rinse with a hose if you’re carful but don’t spray it ever.
take the battery out. Take the battery tray out. That’s usually pretty dirty and you can pressure wash it out of the engine.
Just don’t get wires or sensors wet and you’ll be good. Don’t worry if you do they are protected from moisture mist but if you start spraying everything everywhere it’s gonna get in there somewhere and break something
oh and remember. Coat the battery’s terminals in dielectric grease when you put it back.
Wet down a cold engine and bay then spray generously with diluted wheel acid... Let it sit for a few minutes (don't let it dry tho) then start the engine and go to town with a pressure washer from the top. If / when the engine stops rember where you we're pointing the pressure washer when it died and you'll know which bit you broke. 🤣
I'd love to say I was joking... But...