240sx – Hard starting when cold

From the EF (Engine Fuel) & EC (Emission Control System) section – Diagnostic Procedure #4 / Hard to Start or Impossible to Start when Engine is Cold:

** 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 Air Regulator – When pinching the Air Regulator hose, does the engine speed drop? No = Check Air Regulator and circuit. Yes = Continue.

** Check IAA valve. When pressing accelerator pedal fully, can you start the engine? Yes = Check IAA valve and circuit. 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 Spark Plugs – Remove spark plugs and check for fouling, etc.

** Check ECU Harness Connector

** Check ECU Power Supply and Ground Circuit.

** Try a known good ECU (The ECU may be the cause of the problem, but this is rarely the case!)