1. Fuel System:
* Empty Tank/Fuel Pump: The most obvious. Check your fuel gauge, but even if it shows fuel, the gauge could be faulty. Listen carefully near the fuel tank while someone turns the key to the "on" position (don't crank). You should hear a brief whirring sound – that's the fuel pump priming. If you don't hear it, the pump might be dead or the fuel pump relay is bad.
* Clogged Fuel Filter: A clogged filter restricts fuel flow. It's relatively inexpensive and easy to replace.
* Fuel Pressure: This requires a fuel pressure gauge. The pressure should be within the specifications listed in your owner's manual (or a repair manual for your specific engine). Low pressure indicates a problem with the pump, filter, regulator, or lines.
* Fuel Injectors: They might be clogged or failing. This requires more advanced diagnostics (often involving a scan tool).
2. Ignition System:
* Distributor (If applicable): Older S10s might have distributors. Check the rotor and cap for cracks, corrosion, or worn contacts. The ignition coil could also be faulty.
* Ignition Module/Coil: These components can fail and prevent spark. Visual inspection for damage and testing with a multimeter might be necessary.
* Cranking Speed: If the engine cranks slowly, the battery may be weak or the starter motor is failing. A slow crank can prevent enough power for the ignition system.
3. Air Intake System:
* Air Filter: A severely clogged air filter can restrict airflow enough to prevent starting.
4. Sensors:
* Crankshaft Position Sensor (CKP): This sensor tells the computer the position of the crankshaft, essential for timing the spark. A faulty CKP sensor will prevent the engine from starting.
* Cam Position Sensor (CMP): Similar to the CKP, but for the camshaft. (Some engines may not have this.)
* Mass Airflow Sensor (MAF): While less likely to prevent starting entirely, a severely dirty or faulty MAF sensor can cause problems.
5. Other Possibilities:
* Security System: If your truck has an aftermarket or factory alarm/immobilizer system, it might be preventing the engine from starting.
* Computer/PCM Issues: A faulty engine control module (PCM) can cause a variety of problems, including a no-start condition. Diagnostics with a scan tool are needed.
* Starter Issues (despite cranking): While it cranks, the starter might not be engaging fully. This would require more detailed mechanical inspection.
Troubleshooting Steps:
1. Start with the basics: Check the fuel level, battery voltage, and air filter.
2. Listen for the fuel pump: Check for the priming sound.
3. Check for spark: Use a spark tester or even a screwdriver (carefully!) to see if there's spark at the spark plug wires.
4. Visual inspection: Look for obvious signs of damage or corrosion in the ignition system, fuel lines, etc.
5. Use a multimeter: Test the voltage at the fuel pump, coil, and other components.
6. Obtain a scan tool: A scan tool (OBD-II reader) can read diagnostic trouble codes (DTCs) that might pinpoint the problem.
If you're not comfortable working on your vehicle yourself, take it to a qualified mechanic. Providing them with the information you've gathered from these troubleshooting steps will help them diagnose the problem more quickly and efficiently.
