difference in analog readings

i am using three different pressure sensor board, each of them containing 5+ sensors. i connected to three analog pins of the arduino. while connecting all the three sensor boards, two of them showing wrong values and if its connect individually its showing right data..Can you please help to sort this problem

am using MPXV5004 pressure sensor http://cache.freescale.com/files/sensors/doc/data_sheet/MPXV5004G.pdf

i found some difficulty to get the screenshot of the circuit digram because right now i don't have that file, i used the same circuit in the data sheet.

and also CD4067 multiplexer...http://www.ti.com/lit/ds/symlink/cd4067b-mil.pdf

each board contains cd4067 multiplexer the each output of the multiplexer connected to the A8,A10 AND A11 of the arduino. the selector pins of the each multiplexer also connected to the arduino (4 pins each multiplexer and total 3 x 4 = 12 pins )...Techinally its working, but the data shows the variations while connecting all 3 analog pins and connecting one analog pin..

thank you