Fuel system

I have a 2001 LX Ford Focus for two months I have presented a problem with the fuel system, the fault it presents: it can circulate with the certain mileage continuously and when carrying the constant acceleration begins to lose strength, bell, until finally stops complete I place one that is at room temperature and me merges again I can travel 20 Ò 30 kilometers without problem and the failure returns.

I hope you can help me with this car's problem

The only way that the fuel pump is refrigerated is with the same fuel

proves with the pond over half of this, if it does the same only change it for a new and original one, but the time to buy it must carry this data
displace Pump failure.
But you must verify in detail since the fuel pump can be very expensive, check the filter (if you change the pump I recommend changing it too), fuel prefilter, fuel pressure, fuel pressure valve, existence of black smoke by the exhaust, among others.