The BSE Sensex fell 1.8 per cent on Friday and posted its biggest weekly fall in more than eight months as concerns about the economy kept investors jittery,but Infosys bucked the trend and rallied on strong quarterly result. The 30-share BSE index fell 1.84 per cent,or 253.24 points,to 13,504.22,its lowest close after the ruling coalition won re-election in mid-May and triggered a strong rally. I have been expecting a fall but not to this extent, said Karvy Stock Broking vice president Ambareesh Baliga. Some foreign funds were selling. Twenty-four index components ended down in choppy trade as a pullback of more than 1 per cent at one stage triggered heavy profit-taking in the last half hour.