Allow wifi weak signal connect

I have 2 ZTE Blades (with 512 Mb RAM) and CM7 **2.3.7** (Kang) from BurgerZ ROM installed on them. One of them - my girl's - can connect to home and other (public i.e. McDonalds) wifi AP's even if it's signal is just one bar (it's about 6-7 meters from home router and there are two perpendicular walls on the way). But my can't do that even if 4 bars. (Also, if it can help, same situation with the gps fixes.) I wondering why two same devices have such different behavior? I heard that there are some patch or something to allow android to connect to wifi AP with weak signal but can't find this solution. I know thac ICS have an option Avoid poor connections but I'm not on ICS and don't want to flash it on my Blade. Please, if you have any information or solution about that, help me to fix my device.