code:

int r0 = 0; // registers.
int r1 = 0;
int r2 = 0;
int count = 0;
int mplexes = 0;  // 0 and 1; the number of multiplexers. Currently, there are 2.
float multiplexOutput = 0;
int incomingByte = 0;
int clientKeepAlive = 0;

float init_X;  // X, Y, Z for the accelerometer
float init_Y;
float init_Z;

String label;

void setup() {

  //4051 multiplexer digital control pins
  pinMode(8, OUTPUT);    // s0
  pinMode(9, OUTPUT);    // s1
  pinMode(10, OUTPUT);   // s2
  
  Serial.begin(19200);
}

void loop() {
  if (Serial.available() > 0) {
    incomingByte = Serial.read();
    if (incomingByte == 'y') {
      clientKeepAlive = 1;      
    }
  }
  
  if (clientKeepAlive) {
    // cycle through both multiplexers

    for (mplexes = 0; mplexes <= 1; mplexes++) {
      
      for (count = 0; count <= 7; count++) {
        r0 = bitRead(count,0);
        r1 = bitRead(count,1);
        r2 = bitRead(count,2);
        
        digitalWrite(8,  r0);
        digitalWrite(9,  r1);
        digitalWrite(10, r2);
  
        multiplexOutput = analogRead(mplexes);


	// GROUP 1
        // 0: Fuel_Level
        if (count == 0 && mplexes == 0) {
		label="Fuel_Level: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
        // 1: WaterTemp
        if (count == 1 && mplexes == 0) {
		label="WaterTemp: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
        // 2: Oil_Pressure
        if (count == 2 && mplexes == 0) {
		label="Oil_Pressure: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
        // 3: Boost
        if (count == 3 && mplexes == 0) {
          label= "Boost: "; 
          float newValue = multiplexOutput * (5.00/1023.00) * 100;
          multiplexOutput = newValue;          
        }

	// GROUP 2
        // 4: Fuel_Pressure
        if (count == 4 && mplexes == 0) {
		label="Fuel_Pressure: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
        // 5: Throttle Position Sensor
        if (count == 5 && mplexes == 0) {
		label="TPS: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
        // 6: Tachometer
        if (count == 6 && mplexes == 0) {
		label="Tachometer: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
        // 7: Speedometer
        if (count == 7 && mplexes == 0) {
		label="Speedometer: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
  
	// GROUP 3
        // Accelerometer (8, 9, 10):
        if (count == 0 && mplexes == 1) {
		label="Accel_X: ";  
	}
        if (count == 1 && mplexes == 1) {
		label="Accel_Y: ";  
	}
        if (count == 2 && mplexes == 1) {
		label="Accel_Z: ";  
	}
        // 11: 
        if (count == 3 && mplexes == 1) {
		label="Sensor13: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}

	// GROUP 4
        // 12: 
        if (count == 4 && mplexes == 1) {
		label="Sensor14: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
        // 13: 
        if (count == 5 && mplexes == 1) {
		label="Sensor15: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
        // 14: 
        if (count == 6 && mplexes == 1) {
		label="Sensor16: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}
        // 15:
        if (count == 7 && mplexes == 1) {
		label="Sensor17: "; 
		multiplexOutput = map(multiplexOutput,1,1023,0,100); 
	}


  
        Serial.print(label); Serial.println(multiplexOutput,0); 
      }
      
    }
    Serial.println("*");  
    clientKeepAlive = 0;
  }
}