1. Fuel System:
* Fuel Pump: The fuel pump might be failing to deliver fuel to the engine. You could listen near the fuel tank for the hum of the pump when you turn the key to the "on" position (but not cranking). A lack of humming suggests a failed pump or a blown fuse/relay.
* Fuel Filter: A clogged fuel filter restricts fuel flow. This is a relatively inexpensive part to replace.
* Fuel Injectors: These might be clogged or malfunctioning, preventing fuel from reaching the cylinders. This requires more specialized tools and knowledge to diagnose.
* Fuel Pressure: A fuel pressure gauge is needed to measure the pressure in the fuel rail. Low pressure indicates a problem within the fuel system.
2. Ignition System:
* Spark Plugs and Wires: Worn or damaged spark plugs and wires can prevent a spark from reaching the cylinders. Inspect them for damage, corrosion, or wear.
* Ignition Coil: The coil provides the high voltage needed for spark. A faulty coil will prevent the engine from starting.
* Distributor Cap and Rotor (if applicable): Check for cracks, corrosion, or worn components. These are common failure points in older vehicles with distributors.
* Crankshaft Position Sensor (CKP Sensor): This sensor tells the computer the position of the crankshaft, crucial for timing the spark. A faulty sensor will prevent starting.
* Cam Position Sensor (CMP Sensor): Similar to the CKP sensor, but for the camshaft. Again, a fault here will prevent starting.
3. Other Potential Issues:
* Battery: Although it's cranking, a weak battery might not provide enough power for the starter *and* the ignition system simultaneously. Test the battery's voltage.
* Starter Motor: While you say the motor *turns over*, a weak starter could be struggling and not providing enough power to consistently start the engine.
* Security System: If your car has an aftermarket or factory alarm/immobilizer, it might be preventing the engine from starting.
* Computer/PCM Issues: A malfunctioning Powertrain Control Module (PCM) can cause a variety of starting problems. This is a more difficult issue to diagnose and usually requires a scan tool.
Troubleshooting Steps:
1. Check the obvious: Look for any blown fuses related to the fuel pump or ignition system. Check the battery voltage.
2. Listen for the fuel pump: Turn the key to the "on" position (don't crank) and listen near the fuel tank for the pump's hum.
3. Inspect spark plugs and wires: Look for obvious signs of damage.
4. If you have basic mechanical skills, consider checking the fuel pressure (requires a gauge).
5. If you are not comfortable working on your car, take it to a mechanic. They have the tools and expertise to diagnose the problem accurately.
Without more information (e.g., are there any warning lights on the dashboard? Does the engine crank strongly or weakly?), it's difficult to pinpoint the exact cause. Systematically checking the above items is the best approach. Remember safety first - disconnect the battery negative terminal before working on any electrical components.
