Cant get the SRF02 to work in seriell mode

Other Hardware Sensors
1

HI!

I have an srf02 attached to a Mega 2560 in seriell mode.
i can see that the sensors led is flashing but i cant get the correct values from it.
the output is

Range: 0
Range: 171
Range: 0
Range: 171
Range: 0
Range: 171
Range: 0
Range: 171
Range: 0
Range: 171
Range: 0
Range: 171

then after a while i just get 0

here is my code

//SRF02

#define srfAdrs 00 // Address of the SRF02
#define rangeCM 84 // Byte for start of ranging data

void setup()
{
Serial1.begin(9600);
Serial.begin(9600);
}

void loop()
{
SRF_Range();
}

void SRF_Range(){

int incomingByte=0;

Serial1.write(byte(00)); // send address byte
delay(100);
Serial1.write(byte(84)); //send command byte
delay(70);

if (Serial1.available() > 0)
{
//Serial.write(byte(94));
incomingByte = Serial1.read(); // read serial response
Serial.print("Range: ");
Serial.println(incomingByte); // write distance measured
Serial1.flush(); // clear buffer
delay(100);
}
}

what is wrong?