1. Fuel System:
* Empty or Low Fuel: Sounds obvious, but check the fuel gauge.
* Fuel Pump: The fuel pump might be failing, not delivering enough fuel to the engine. You might hear a whirring sound from the fuel pump when you turn the key to the "on" position (before cranking). If you don't hear it, that's a strong indication of a fuel pump issue.
* Fuel Filter: A clogged fuel filter restricts fuel flow.
* Fuel Injectors: Faulty injectors might not be spraying fuel into the cylinders.
* Fuel Pressure: A professional mechanic can test fuel pressure to see if it's within specifications.
2. Ignition System:
* Spark Plugs and Wires: Worn, fouled, or loose spark plugs and wires can prevent a spark. Check for visible damage and consider replacing them.
* Ignition Coil: A faulty ignition coil won't provide the necessary spark to ignite the air-fuel mixture.
* Distributor (if applicable): Older Blazers might have distributors; check the cap and rotor for wear or cracks. A faulty distributor could also be at fault.
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational position. A bad CKP sensor prevents the engine from getting the signal to fire.
* Camshaft Position Sensor (CMP): Similar to the CKP, a bad CMP sensor will prevent the engine from starting.
3. Battery and Electrical System:
* Battery: A weak or dead battery might crank the engine slowly, preventing it from starting. Test the battery voltage.
* Alternator: While the alternator charges the battery while the engine is running, a failing alternator can cause starting problems if the battery is already low.
* Starter Motor: Though you say it turns over, a weak or failing starter might not be providing enough power.
* Wiring and Connections: Check for any loose or corroded wiring connections in the ignition system and battery.
4. Other Possible Causes:
* Security System: A malfunctioning immobilizer or alarm system could be preventing the engine from starting.
* Engine Control Module (ECM): A faulty ECM can cause a wide range of starting problems. This is usually diagnosed with a scan tool.
* Sensors: Many other sensors (e.g., oxygen sensor, mass airflow sensor) can affect the engine's ability to start. A diagnostic scan can identify faulty sensors.
Troubleshooting Steps:
1. Check the basics: Fuel level, battery voltage, and obvious visual checks (loose wires, damaged parts).
2. Listen carefully: Pay attention to any unusual sounds during cranking (whirring, clicking, grinding).
3. Use a code reader/OBD-II scanner: This will retrieve any diagnostic trouble codes (DTCs) stored in the ECM, which can point to specific problems. Auto parts stores often offer free code scanning.
4. Test the components: Once you've identified a potential problem area (e.g., fuel pump, ignition coil), you may need to test the component to confirm whether it's faulty. This usually requires some automotive knowledge and tools.
5. Seek professional help: If you're not comfortable performing these checks yourself, take your Blazer to a qualified mechanic for diagnosis and repair.
Don't attempt repairs you're not qualified to handle. Working on a vehicle's electrical and fuel systems can be dangerous if not done properly.
