a fuel injection system for externally ignited engines employing continuous manifold injection includes a fuel metering valve assembly . the control slide of this valve assembly is actuated by the air - flow through the induction manifold and controls the size of fuel flow apertures . a differential pressure valve normally maintains a constant pressure difference across these metering valve apertures . the magnitude of this normally constant pressure difference can be altered in response to signals obtained from or measurements performed on operational parameters of the engine ; for example , the oxygen content of the engine &# 39 ; s exhaust gases .