hi i have a 51 grand cherokee 3.1td.The problem is if the motor has been standing for a week or more it takes alot of cranking to get it started,up to the point when the batteries dies.Once started it will start day after day,but leave it for a week and no joy.To get it started i have to jump it once battery has died.Could it be the fuel running back to the fuel tank,i dont know if these have a non return valve.Could it be a lazy fuel pump.Thanks for any help peter