Use a foam gun, then a dedicated detailers brush. I bought a 5 pieces brush kit off of amazon for 12 dollars. Works amazingly well for unpainted surfaces like behind the grills, wheel wells, and lug nuts.
https://www.amazon.com/Master-Detail...gateway&sr=8-3
Avoid pressure washing any car at high psi. Use a wide nozzle, and a good amount of distance. Do test blasts on the cement, or some other safe area. If it cleans the cement, then it's way too fucking powerful for your car. lol