To correct problems of fuel consumption, you have to use c-magic, create the md3 file of the track you are having problems, open the md3 file and edit it, this file can be open with notebook.
At md3 file, look for two lines with information of fuel consumption, change the numbers, normally I reduce them around 2000 less than the original numbers.
Save the file, and insert the new md3 data in the .dat file of the circuit.
If the problems continues, do the same process and reduce more the values for fuel consumption.