I would not use any high pressure commercial spray. It can, and will drive water into places where you don't want it. Instead, buy a garden spray unit, which you can pressurize at a low level, and use a good degreaser/solvent, followed by elbow grease with a brush. And then rinse, using the same sprayer.
+1 on not using a pressure washer. A degreasing solution and old paint brushes or dish washing brushes, spray again with the degreasing solution then rinse well with water. Remove the distributor cap & wires, cover the distributor by taping a plastic bag around it & cover the spark plug holes with tape or corks.
I wrap the distributor with rags and go nuts with my gas pressure washer. Im always careful of course to avoid the spark plug leads on the valve covers as much as possible
if some gets in there I just dry it out with a rag...no big deal. I usually wash the engine every time I wash the car, as it maintains at a clean level easily whereas leaving it, would just build up.
Beforehand, I soak and scrub with a good degreaser like simple green, as no amount of water can dissolve grease and grime.
BTW in some places you are fined for washing engines, as its not exactly environmentally friendly...in other words be careful that you neighborhood drain does not have a fish symbol on it or something...in fact do it on your own property, or at a car wash (which some have filtration). believe me...neighbors will complain about everything!
li9ke said above..i do it every time i wash the car..regardless of what car i may be driving...and yes neighbors can and will throw a tantrum over that crap...so do it where it cant be seen or do it at a coin op
ive been doing engines in the coinop for as long as i can remember...and 99% of the time i dont even wrap the dizzy..out of more times than i can count have i had a car that wouldnt start due to water in the dizzy and 5 mins later they did start.(those were the only ones that later got wrapped at the wash being a toyota celica and an audi coupe)...sure you want to try and keep water out of the dizzy but outside of that GO NUTS with the pressure....
just remember this ...the firewall in a gtv6 has padding on it that will SHREAD under pressure as will the hood liner
You can quite safely blast away at the engine below the injectors and engine bay below rocker covers and not damage much. Just don't go waving the pressure washer willy nilly at electrical connectors etc. In other words, just use it sensibly.
I always hose down the entire engine bay with engine degreaser and then rinse off with a garden hose. I've done this countless times on numerous cars and never had a single issue.
I use gas oil with a brush, particularly for difficult areas and near electrical wires & stuff. Then I clean with a rag.
Results are quite good, with an oily-effect which, IMO, helps keeping away possible rust.
About 10 years ago I bought an '86 Saab SPG. The owner had pressure washed the engine before I picked it up. About a mile from his house it died. Upon inspection there was water in the three of the cylinders, now with crispy rings, and the distributor was blown apart from the inside. I got my check back, he got a ruined car. At least he admitted his own fault in the matter!
Moral: Save the pressure washer for the driveway. Just get a garden soaker with a stream setting, some of the burly purple degreaser, an assortment of brushes and some heavy PVC gloves, and put some back into it. You can probably get everything at Harbor Freight for less than $25.