Allows Correct Installation of the High-Pressure Fuel Pump by Ensuring the Fuel Pump Camshaft Lobe is on the Base Circle. Before installing the new fuel pump, insert the correct gauge into the engine. If the lip of the gauge does not sit flush to the engine, turn the camshaft until the gap is gone. Misalignment and improper torqueing of the bolts could lead to damage to the fuel pump or engine camshaft. Used on late model GM Direct Injection engines including 2.5L, 3.6L VVT, 5.3L and 6.2L.