240sx – Hard starting when hot

From the EF (Engine Fuel) & EC (Emission Control System) section – Diagnostic Procedure #5 / Hard to Start or Impossible to Start when Engine is Hot:

** Fuel Pressure – Squeeze the line coming out of the filter and to the engine when cranking the car. You should feel pressure. No = Check the fuel pump and it’s circuit. Yes = Continue

** Check Fuel Vapor – Disconnect fuel pressure regulator vacuum hose and plug the hose. Can you start the engine? Yes = Check fuel properties (don’t know what this actually means) No = continue

** Check Injector – Remove crank angle sensor (distributor) from engine.Be sure to note the location and orientation of the rotor before taking the CAS out of the engine. It needs to go back the same way (Crank angle sensor harness connector should remain connected) Disconnect ignition coil harness connector. Turn ignition switch on (Do not start engine) When rotating crank angle senor shaft (distributor), does each injector make an operating sound? No = Check injectors and circuit. Yes = Continue

** Check Ignition Spark – Disconnect ignition wire from installed spark plug. Connect a good known spark plug to the ignition wire. Place end of spark plug against a suitable ground and crank engine. Check spark.No Good = Check ignition coil, power transistor unit, and circuits. Yes = Continue

Check ECU Harness Connector

Check ECU Power Supply and Ground Circuit.

Basically, what’s being looked at here is if the engine is getting fuel, the injectors are injecting and the spark is sparking. The ECU part is standard fare in diagnosing our car.