1. Fuel System Issues:
* Empty Gas Tank: The most obvious reason! Check the fuel gauge.
* Fuel Pump Failure: The fuel pump moves gas from the tank to the engine. A faulty pump won't deliver fuel. You might hear a humming sound from the pump when you turn the key if it's trying to work but failing.
* Clogged Fuel Filter: A dirty fuel filter restricts fuel flow.
* Fuel Injector Problems: Injectors spray fuel into the engine. Clogged or faulty injectors prevent proper fuel delivery.
* Bad Fuel Pressure Regulator: This component maintains proper fuel pressure. A malfunction can lead to too much or too little pressure.
2. Ignition System Issues:
* Dead Battery: A low or dead battery won't provide enough power to crank the engine. Check the battery voltage with a multimeter.
* Corroded Battery Terminals: Corrosion prevents good electrical connection. Clean the terminals.
* Faulty Starter Motor: The starter motor cranks the engine. A bad starter won't turn the engine over. You might hear a clicking sound.
* Ignition Switch Problems: The ignition switch might be faulty, preventing power from reaching the starter.
* Bad Ignition Coil: The coil provides the high voltage needed for spark plugs.
* Spark Plug Issues: Worn, fouled, or damaged spark plugs prevent ignition.
* Ignition Wiring Problems: Damaged or loose wires can interrupt the electrical signal.
3. Engine Problems:
* Timing Belt Broken: A broken timing belt means the engine won't run. This is a serious problem requiring professional repair.
* Low Compression: If the engine's compression is too low, it won't start. This could be due to worn rings, valves, or head gasket issues.
* Camshaft Position Sensor or Crankshaft Position Sensor Issues: These sensors tell the computer the position of the engine components for proper timing. A faulty sensor will prevent starting.
4. Other Issues:
* Immobilizer System: Some 4Runners had an immobilizer system that prevents starting if the correct key isn't used.
* Security System: An aftermarket alarm or security system could be malfunctioning.
* Alternator Problems: While the alternator charges the battery, a failing alternator can prevent the engine from starting if the battery is already weak.
Troubleshooting Steps:
1. Check the obvious: Gas level, battery terminals, and try a different key (if applicable).
2. Listen for sounds: A clicking sound might indicate a starter problem; a humming sound could point to the fuel pump.
3. Check the battery voltage: Use a multimeter to ensure the battery is charged.
4. Check spark: If you have experience, you can check for spark at the spark plugs.
5. Consult a repair manual: A repair manual specific to your 1997 Toyota 4Runner will provide detailed troubleshooting steps and diagrams.
It's crucial to systematically check these possibilities. If you're not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair. Providing more details about the symptoms (e.g., clicking sounds, cranking but not starting, no sound at all) would help narrow down the possibilities.
