1. Fuel System:
* Empty Tank: The most obvious! Check your fuel gauge.
* Fuel Pump: Listen for the whirring sound of the fuel pump when you turn the key to the "on" position (before cranking). A lack of sound suggests a faulty pump or relay.
* Fuel Filter: A clogged fuel filter restricts fuel flow. This might require replacement.
* Fuel Injectors: These spray fuel into the cylinders. A problem here could be caused by a faulty injector, low fuel pressure, or a problem with the fuel injector control module (FICM). This often requires professional diagnosis.
* Fuel Pressure Regulator: A malfunctioning regulator can cause incorrect fuel pressure.
2. Ignition System:
* Spark Plugs: Worn, fouled, or damaged spark plugs prevent ignition. Inspect them for wear and consider replacing them.
* Ignition Coils: These deliver high voltage to the spark plugs. A faulty coil will prevent one or more cylinders from firing.
* Ignition Wires (Spark Plug Wires): Cracked or damaged wires can prevent a spark from reaching the plugs.
* Distributor (Older Vehicles): If your car has a distributor, check its cap and rotor for wear or damage.
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational position. A faulty CKP prevents the ignition system from firing.
* Cam Position Sensor (CMP): Similar to the CKP, but for the camshaft. A faulty CMP will also prevent proper firing.
3. Air Intake System:
* Air Filter: A severely clogged air filter restricts airflow, leading to poor combustion.
* Vacuum Leaks: Leaks in the intake system can disrupt the air-fuel mixture.
4. Battery and Starting System:
* Weak Battery: Even if the engine cranks, a weak battery might not provide enough power to consistently fire the ignition system. Test the battery voltage.
* Battery Terminals: Corroded or loose battery terminals can prevent sufficient current flow. Clean and tighten them.
* Starter Motor: While you say it cranks, a weak or failing starter might not spin the engine fast enough for reliable ignition.
5. Computer and Sensors:
* ECU (Engine Control Unit): Problems with the ECU can prevent the engine from starting. This requires advanced diagnostic tools.
* Other Sensors: Various sensors (e.g., oxygen sensor, mass airflow sensor) can affect engine operation and prevent starting if faulty.
Troubleshooting Steps:
1. Check the obvious: Fuel level, battery terminals, and air filter.
2. Listen for the fuel pump: Should hear a whirring sound when the key is turned to "on."
3. Inspect spark plugs: Look for wear, fouling, or damage.
4. Check for error codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the ECU. This is often the fastest way to pinpoint the problem.
When to Seek Professional Help:
If you're not comfortable working on your car, or if you've checked the easy things and still can't find the problem, it's best to take it to a qualified mechanic. They have the tools and expertise to diagnose more complex issues. Providing them with any codes you've found will help them immensely.
