What P0087 usually means
P0087 means the engine management system believes actual fuel rail pressure is too low for the operating conditions. On gasoline direct-injection vehicles that often means the rail cannot keep up with commanded pressure under load. On other systems it can still point to a weak supply side, restriction, regulator problem, or an inaccurate pressure reading. The important split is whether the pressure really is low or whether the sensor and control story only looks that way.