advice needed for arduino as diesel injection brain...

PeterH is correct, I did not write the sketch properly. I need a signature under my avatar that says "Warning Novice on board!" .

I rewrote the return sketch, I think it is correct this time. Sorry for the mistake I made earlier.

const int ledPin =  13;      // the number of the LED pin

// Variables will change:
int DonesAnswer = 0;           // variable to pass "done" to         

long previousMillis = 0;        // will store last time LED was updated

long interval = 1200;           // interval at which to blink (milliseconds)

void setup() {
  // set the digital pin as output:
  pinMode(ledPin, OUTPUT);   
  Serial.begin(9600);  
}

void loop()
{

  unsigned long currentMillis = millis();

  if(currentMillis - previousMillis > interval)
  {
    // save the last time you blinked the LED 
    previousMillis = currentMillis;   

   DonesAnswer = whatdonedoes();   // transfer "done" to DonesAnswer using the function

    Serial.print("done = ");
    Serial.println(DonesAnswer);

    digitalWrite(ledPin, DonesAnswer);
  }
}

////////////////////////////////function with a return called done//////////
int whatdonedoes()
{
  static int done = 0;  //set done to static int

  // if the LED is off turn it on and vice-versa:
  if (done == 1)
    done = 0;
  else
    done = 1;

  return done;
}