for most of my details of the engine bay I spray simple green down to loosen up grime/dirt and let it sit for about 5 minutes. I then take a hose and carefully hose the engine bay down, avoiding contact with distrubutors, alternators, intakes(I put a bag over the intake if its' exposed and not in a airbox). after the motor dries, I usually use a silicone based product like tire shine and put it on a rag to wipe down hoses and black plastic parts, avoiding contact with electrical connectors to avoid damage to them. It always comes out pretty good, just gotta take your time and be careful as to what you spray/wipe to avoid damage. Doesn't matter if a car looks good if it won't run.