A single plunger high pressure fuel pump including a low pressure infeed leading to a pumping chamber, a pumping plunger for pressurizing fuel in the pumping chamber during a pumping stroke, an outlet valve for delivering pressurized fuel from the pumping chamber to a high pressure outlet line during the pumping stroke, an overpressure relief valve with relief inlet connected to the high pressure outlet line and exit (10") connected to the pumping chamber, wherein the relief valve comprises a valve element that is spring biased against a relief valve seat sealing the inlet, the spring applies the bias to the valve element through a piston, the piston has one end that loads the valve element and another end that is loaded by said spring, and the spring is in a spring chamber connected to the low pressure infeed of the pump, and said one end of the piston is in hydraulic communication (10', 10", 10"') with the pumping chamber and said other end of the piston is in said spring chamber: the piston is slidable in a bore, and in a forward position within the bore the piston loads the valve element against said seat; the piston is displaceable in the bore a first distance away from said seat by the valve element when the valve element is opened by the force differential between fuel pressure in the relief inlet exceeding the spring load and exceeding fuel pressure in the pumping chamber, whereby fuel in the relief is dumped through said seat into the pumping chamber; the piston is displaceable in the bore a second distance greater than said first distance from said seat by the valve element when the valve element is opened by the force differential between fuel pressure in the relief inlet exceeding the spring load and the fuel pressure in chamber exceeding the fuel pressure in the relief inlet; characterized in that the piston has a spill connection with an entry port in hydraulic communication with the pumping chamber, and a spill port that is covered by the piston bore while the piston is at said forward position or displaced less than said second distance, and said spill port is in hydraulic communication with said spring chamber when the piston is displaced at least said second distance; whereby when the fuel pressure in chamber exceeds the fuel pressure in the relief inlet, the fuel pressure in said pumping chamber is relieved to the low pressure in said low pressure infeed. the piston is slidable in a bore, and in a forward position within the bore the piston loads the valve element against said seat; the piston is displaceable in the bore a first distance away from said seat by the valve element when the valve element is opened by the force differential between fuel pressure in the relief inlet exceeding the spring load and exceeding fuel pressure in the pumping chamber, whereby fuel in the relief is dumped through said seat into the pumping chamber; the piston is displaceable in the bore a second distance greater than said first distance from said seat by the valve element when the valve element is opened by the force differential between fuel pressure in the relief inlet exceeding the spring load and the fuel pressure in chamber exceeding the fuel pressure in the relief inlet; characterized in that the piston has a spill connection with an entry port in hydraulic communication with the pumping chamber, and a spill port that is covered by the piston bore while the piston is at said forward position or displaced less than said second distance, and said spill port is in hydraulic communication with said spring chamber when the piston is displaced at least said second distance; whereby when the fuel pressure in chamber exceeds the fuel pressure in the relief inlet, the fuel pressure in said pumping chamber is relieved to the low pressure in said low pressure infeed.