Fuel System Issues (despite seemingly good fuel pump relay/switch):
* Low Fuel Pressure: The relay/switch might be okay, but the fuel pump itself could be weak, failing, or clogged. A pressure gauge connected to the fuel rail is needed to confirm sufficient pressure. The fuel filter could also be clogged, restricting fuel flow.
* Fuel Pump Inertia Switch: Some vehicles have an inertia switch (a safety device that cuts fuel in a collision) that might have tripped. Locate this switch (often under the dash or in the engine bay) and reset it.
* Fuel Injectors: The injectors might be clogged, faulty, or not receiving the proper electrical signal to open and spray fuel. A diagnostic scan tool can check injector pulse.
* Fuel Delivery Problems: A kinked or damaged fuel line can restrict fuel flow, even if the pump is working.
Ignition System Issues:
* Spark Plugs/Wires: Worn, fouled, or damaged spark plugs or ignition wires can prevent a spark strong enough to ignite the fuel-air mixture.
* Ignition Coil: A failing ignition coil won't provide the necessary high voltage to the spark plugs.
* Crankshaft Position Sensor (CKP) or Camshaft Position Sensor (CMP): These sensors tell the computer the engine's position, crucial for timing the spark. A faulty sensor will prevent ignition.
* Ignition Control Module (ICM): The ICM controls the ignition system; a failure here can prevent sparking.
Other Potential Problems:
* Mass Airflow Sensor (MAF): A faulty MAF sensor provides inaccurate air/fuel readings to the computer, leading to improper fuel delivery and potential no-start conditions.
* Computer (PCM): Though less likely, a faulty Powertrain Control Module (PCM) can cause a wide range of problems, including a no-start condition. A diagnostic scan code reading is crucial here.
* Security System: The car's anti-theft system could be preventing the engine from starting.
Troubleshooting Steps:
1. Diagnostic Scan: The most important step is to get the car scanned with an OBD-II code reader. Error codes can pinpoint the issue quickly.
2. Check Fuel Pressure: Use a fuel pressure gauge to verify sufficient pressure at the fuel rail.
3. Inspect Spark Plugs and Wires: Visually inspect for damage or fouling.
4. Check Fuel Pump Operation: While the relay might seem good, listen closely near the fuel tank for the pump's whirring sound when the ignition is turned on.
5. Verify Injector Pulse: Use a scan tool to check if the injectors are receiving the correct signal to fire.
6. Check Crankshaft/Camshaft Position Sensor: These sensors can often be checked for voltage with a multimeter.
Don't overlook the seemingly simple things. Double-check all connections and fuses related to the fuel system and ignition. If you're not comfortable working on your car's electrical system, a qualified mechanic is the best option to avoid further damage.
