Abstract: Modification of the existing system of fuel injection pump, of a kind which moves little pistons catching controllable fuel amount, and compress such fuel until it is forced out through an injector. In the pump used at the present, the mentioned pistons force the fuel to move without returning; in the proposed modification these same pistons move a different fluid, with better lubricating features than fuel, in both directions. The alternative displacement of this different fluid produces pressure variations which are indirectly transmited to fuel through an elastic element (14a) that separates the fuel from the other fluid within a hermetically sealed space. Due to the pressure variations induced on the fuel in that way, the fuel is forced to flow toward the injector, by using in its run, suitable inlet (17) and (18) valves. The before mentioned is shown in the figures 2, 2A, 3 and FIG. 2A and 3A.