I'll update later with better soap, higher psi air, and a video in the day.
This is to keep the soap suds on the car as long as possible to break up the bugs. I was playing in the garage one night. I have seen compressed air car wash foam guns that are $100+ , compressor foam cannons which are $100 or so, and foam hose guns that are $40-$60 First I though use a harbor freight cheap car paint gun with soap in it. Harbor freight was closed to try it. How do you get compressed air out the end of your hose sprayer? Think one way valve; so I made one. Here's how. The video shows using air at about 40 to 60psi due to the time at night I finished and not wanting to turn my compressor on and piss of the neighbors. Higher psi would probably produce more foam, esp if it had a chamber or hose between the chamber and hose y connector to mix the soap and air in more prior to ejection. Notice the 1/4" hose coming out of the hose Y. It's the air flowing against the current of the soapy water from a injection device = Green Earth G-Clean High-Pressure Detergent Injector for Pressure Washers that was $15 Model #: AUN31024D. see later pics.
Too bad I later found a $20 green earth cannon for my pressure washer on amazon that works okay. This will work well if you do not have a pressure washer, but do have a compressor. Just get some Detailers Pro Extreme Foam Soap and increase the air pressure and turn down the water at the hose Y as much as possible with your fan spray so the soap is compressed as much as possible with as little water as possible.
One way Valve attached to half of the green earth soap injector's extra hose from the kit attached to a hose Y connector. To narrow the air entering the hose/soapy water I used a patio irrigation 1/4" hose and a inline irrigation male-to-male connector and shaved down the edges to squeeze into the green earth clear tube so that the thinner stream of air would create more bobbles think coffee star vs Slurpee straw in milk and the size of bubbles then add 100 psi. Then it all comes out of the hose sprayer. I chose the two sprayers because one is a gun for on and off and the other can create a fin fan mist better than the 6-in-one sprayers etc.