teckel:
Analog or digital pins is not the issue. The shield has nothing to do with the sonar sensors, so your confusing things by even including it. And you're still trying to get 4 sensors working before you successfully have one working. Maybe you have 4 bad sensors? No way to tell with the method you're using to build/write this. Strip everything down to just the Arduino, sensor, and 4 wires to it. Make sure it works with the sample sketch. Walk first or you'll never figure out the problem.
I'm home now and I've sorted it out, thanks God. The problem was the L293D shield, after removing it the ultrasonic sensors had good reading. I've moved the pins from digital to analog 0-3. Now it's much better:
sonar0: 19
sonar1: 4
sonar2: 23
sonar3: 7
sonar0: 19
sonar1: 4
sonar2: 23
sonar3: 7
sonar0: 19
sonar1: 4
sonar2: 23
sonar3: 8
sonar0: 19
sonar1: 4
sonar2: 23
sonar3: 7
Many thanks for helping me out.. i tough it was a big problem but it always the little things that complicate us.