Using Multiple PING))) Ultrasonic sensors

I haven't run the following but I hope it gives you an idea of how you can simplify your sketch and control the delay between each ping

int ultraSoundSignalPins[] = {8,7,6,9}; // Front Left,Front, Front Right, Rear Ultrasound signal pins
char *pingString[] = {"Front Left ","Front ", "Front Right ", "Rear "}; // just something to print to indicate direction

void setup()
{
  Serial.begin(9600);
}

//Ping function
unsigned long ping(int index)
{
  unsigned long echo;

  pinMode(index, OUTPUT); // Switch signalpin to output
  digitalWrite(index, LOW); // Send low pulse
  delayMicroseconds(2); // Wait for 2 microseconds
  digitalWrite(index, HIGH); // Send high pulse
  delayMicroseconds(5); // Wait for 5 microseconds
  digitalWrite(index, LOW); // Holdoff
  pinMode(index, INPUT); // Switch signalpin to input
  digitalWrite(index, HIGH); // Turn on pullup resistor
  echo = pulseIn(index, HIGH); //Listen for echo
  return (echo / 58.138) * .39; //convert to CM then to inches
}

void loop()
{
  unsigned long ultrasoundValue;
  for(int i=0; i < 4; i++){
    ultrasoundValue = ping(i); 
    Serial.print(pingString[i]);
    Serial.print(ultrasoundValue);
    Serial.print("in, ");    
    delay(50);

  }
  Serial.println();
  delay(50); 
}