You know the feeling. You hop in the driver's seat and twist the key (or push the start button). Your engine cranks. And cranks. And cranks. But your car simply refuses to start. That's when your mind starts racing: What could be the problem?
An engine needs three basic things to run: fuel, spark and compression. If any of these three essentials is missing, it won’t start.
Here are common reasons your car’s engine might turn over but not fire up.
Out of Gas
Even if your car’s fuel gauge is showing plenty of fuel, you could still be out of gas. Sometimes the gauge itself is faulty. A quick way to test this is to add some fuel to the tank and try again to start the engine. If it fires up, that means there's an issue with either the gauge or the sending unit in the tank, which measures and reports the fuel level.
If the engine still won't start after adding fuel, the problem lies elsewhere.
Bad Fuel Pump or Clogged Fuel Filter
A bad fuel pump or clogged fuel filter can also starve the engine of fuel. Fuel pumps in modern cars are electric and push fuel from the tank to the engine. They can suffer from electrical failures or simply wear out over time. To check if yours is still working, turn the ignition to the "on" position (without cranking the engine) and listen for a slight hum from underneath the car. Hearing that sound indicates the fuel pump is still operational; otherwise, it may be time for a new one.
A functioning fuel pump doesn’t rule out issues with fuel flow, however. It could be the fuel filter, which protects the engine by trapping debris from the fuel tank. It can become clogged with use, restricting or even stopping the flow of fuel. To assess its condition, check for a date or mileage on the outside of the canister; mechanics usually note this when installing a new unit. If it's been over 30,000 miles or three years since the last change, replacing the filter might resolve the issue.
Defective Ignition Coil
Once you rule out a lack of fuel, the next thing to check for is the lack of spark. A defective ignition coil is often the culprit here. When working properly, the coil transforms the battery's low voltage into the high voltage needed to run the engine. A defective coil, on the other hand, can cause a range of problems, from engine misfires to a complete refusal to run.
Diagnosing faulty ignition coils begins with a visual inspection, looking for cracks or other damage. If that doesn't identify the issue, try the spark test. This involves removing the coil and spark plug from the cylinder and reconnecting them outside the cylinder head. Place the exposed plug on a grounded surface and observe it while someone cranks the engine. It should produce a series of glowing blue sparks. If not, that coil likely needs replacing.
Faulty Sensors
The crankshaft and camshaft sensors monitor the positions of those components while the engine is running. The information they provide helps the engine control unit (ECU) coordinate the timing of fuel injection and ignition at each cylinder. If either sensor is malfunctioning, it can prevent the engine from starting.
To confirm a sensor issue, use a diagnostic scanner, also known as a code reader, which plugs into the car's OBD-II port. If you find any related error codes, check the sensor and its connections for any obvious issues before opting to replace it. Be sure to use the scan tool again after replacing a faulty sensor to reset the error code and verify that the issue is resolved.
Broken Timing Belt or Chain
All engines have a timing belt or chain that connects the crankshaft to the valvetrain, ensuring the two are properly synchronized. If this belt or chain snaps, the valves and pistons cease to operate in unison. This not only prevents the car from starting but can send the pistons crashing into the valves, triggering catastrophic engine damage.
The most telling sign of a broken timing belt or chain is the engine cranking at an unusually fast rate. This happens because the resistance usually provided by the valvetrain is absent. If you encounter this, do not attempt to start the engine again. This can cause further damage. Instead, open the timing cover, usually located at the front of the engine, to confirm the belt or chain isn’t worn or broken before proceeding with your repairs.
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