1. Fuel System Issues:
* Empty or low fuel: The most obvious reason! Check the fuel gauge.
* Fuel pump failure: The pump might be broken, not delivering fuel to the engine. You might hear a whirring sound when you turn the key if the pump is trying to work but failing.
* Clogged fuel filter: A dirty fuel filter restricts fuel flow.
* Fuel injectors malfunctioning: Injectors might be clogged or electrically faulty, preventing fuel from being sprayed into the cylinders.
* Bad fuel pressure regulator: This regulates the fuel pressure; a malfunction can lead to inconsistent fuel delivery.
2. Ignition System Problems:
* Dead battery: The most common cause. Check the battery voltage with a multimeter. Jump starting can confirm this.
* Faulty starter motor: The starter might be worn out or have a bad connection. You might hear a clicking sound when you turn the key.
* Bad ignition switch: The switch might be faulty and not sending power to the starter or ignition system.
* Ignition coil failure: The coil doesn't generate the high voltage needed for the spark plugs.
* Worn spark plugs or wires: Spark plugs can become fouled or worn, preventing a spark. Worn wires can reduce or prevent spark delivery.
* Distributor cap and rotor problems (if applicable): These components distribute the high voltage to the spark plugs; cracks or corrosion can disrupt this.
3. Engine Problems:
* Timing belt failure: A broken timing belt will prevent the engine from turning. This is a serious issue requiring significant repair.
* Compression issues: Low compression in one or more cylinders prevents the engine from firing properly. This could be due to worn piston rings, valve problems, or a blown head gasket.
4. Other Potential Issues:
* Security system problems (if equipped): An immobilizer or alarm system might be preventing the engine from starting.
* Faulty crankshaft position sensor (CKP): This sensor tells the engine's computer where the crankshaft is, and a malfunction will prevent starting.
* Faulty camshaft position sensor (CMP): Similar to the CKP, but for the camshaft.
* Corroded or loose connections: Check all battery terminals, ground wires, and other electrical connections for corrosion or looseness.
Troubleshooting Steps:
1. Check the obvious: Fuel level, battery voltage.
2. Listen for sounds: Clicking (starter), whirring (fuel pump).
3. Check fuses: Inspect the fuses related to the ignition system.
4. Visual inspection: Look for obvious problems like loose wires or damaged components.
If you're not mechanically inclined, it's best to take your 1990 Corolla to a qualified mechanic for diagnosis and repair. Trying to fix some of these issues without experience can be dangerous and potentially lead to more damage.
