Carrier 58ssb.we replaced control brd,sensor,ignitoin modul,and still doing the same .pilot ignit but main valve doesn't open up.all safety OK,wire harness OK.I have only 8 volt going 2 main valve.

Need roughly 24v to main valve to open. The money you have spent replacing parts could have easily paid for a pro to come fix your problem. Have you checked pressure swithces? Need to find why you are not getting proper voltage at gas valve.

I did by pass it.its weird ,ground is good,checked every thing all seems to be OK but I am not getting 24 v 2 main valve.

Take the wires off the main valve and measure the voltages during the pilot and main valve phase.