teckel:
All of my HC-SR04 sensors work with both 2 pins and 1 pin, so it has nothing to do with the pins. Who did you purchase your sensors from as I'd love to duplicate the problem.
I got them from this vendor on Amazon http://www.amazon.com/gp/product/B0085MXZH0/ref=oh_details_o01_s00_i00
They're currently out of stock, so replacements you get may or may not be the same batch.
teckel:
Also see the attached file to this message. This modified version of the library simulates the pulseIn function that's being used the example sketch you linked to (waits up to a second for a ping echo). I would not suggest anyone else using this library, it's just meant for testing for those with a HC-SR04 that are giving 0cm results. It's an inferior library just meant for testing.Let me know how this works.
I'll try that out tomorrow and report back. Thanks for your help!