Techniques for measuring fuel injector flow irregularity without removal from vehicle

A diagnostic method for a fuel system of an engine of a vehicle, the method comprising:

• obtaining, by a controller and from a fuel rail pressure sensor, a measured fuel rail pressure indicative of a pressure of a fuel in a fuel rail of the fuel system, wherein the fuel rail provides the fuel to fuel injectors of the fuel system;
• obtaining, by the controller and from an engine speed sensor, a measured engine speed indicative of a rotational speed of a crankshaft of the engine;
• obtaining, by the controller and from an exhaust oxygen (O2) sensor, a measured O2 concentration indicative of an oxygen level of exhaust gas produced by the engine;
• and
• performing, by the controller, a diagnostic routine for the fuel system during which the fuel injectors do not need to be removed from the engine, the diagnostic routine comprising:
• operating, by the controller, the engine at a set of predetermined operating points;
• and
• detecting, by the controller, one or more malfunctions of one or more of the fuel injectors while the one or more fuel injectors remain installed on the engine based on the measured fuel rail pressure, the measured engine speed, and the measured O2 concentration at each of the set of predetermined operating points.