OBD1 (GM) DIY Scan Tool Arduino Leonardo

Recently I have been bored and have been trying to figure out how to make an OBD1 to USB serial convertor. My design is based off this guy's right here I wired my Arduino like the picture I made.
I tried this code here

void setup() {
  Serial.begin(9600); //I know what this does
}
byte rx_byte = 0;         //No idea what this does really(Same for the rest of the code)

void loop() {
if (Serial.available()) 
    rx_byte = Serial.read(); 
}

I was not able to receive any information from the port through the serial monitor, and if I am actually receiving information, how could I make sure the data gets to this software or any others?
P.S. I'm trying to read data from a 1994 Chevy Cavalier Z24 3.1L V6
P.P.S I know this may not be the right place to ask this kind of stuff

Not all OBD1 networks use 9600 baud. I have not idea if the information in this link is good, but you could try different baud rates. If you have access to an oscilloscope have a look and see what it is.

Thank you, I did not think about different baud rates.