electric problem

I have a circle of track split in half, two blocks. running the engines on conventional control. I am under construction and have both blocks tired together and the trains have been running well. Today the engine would run fine until it entered the next block and would slow to almost a stop. I check the voltage with the engines running,three different engines and the volts were the same in a half dozen locations.I also check the voltage with NO engines on the track and was getting 20V at each check point.