Main reasons why engine cranks but won't start!
Our car breakdown service gets called every day for many reasons, one of them being "my car doesn't start". Everyone automatically assumes that the vehicle needs a battery boost. However, there are few reasons why the engine cranks, but it won't start, and here are the main reasons:
To start running under its own power, an engine needs four essential things: air, fuel, compression, and spark. An engine with low compression can be difficult or impossible to start, meaning seals and gaskets could leak into the engine. You may need things like new valve seals, new piston rings, or other components replaced so that the engine can withstand the intense pressure it needs to run.
Clogged Fuel Injectors
If the car cranks when you turn the key, but the engine won't start, it could be because fuel isn't getting to the engine.
One potential reason for this could be dirty fuel injectors. Over time, the fuel injector nozzles can become clogged with rust, corrosion, or debris. Once clogged, the fuel injectors may not add the correct amount of fuel to the cylinders, and the vehicle may not start up.
Only add high-quality gasoline to the tank to keep your fuel injectors clean and working as intended. Gasoline from less-than-reputable sources that have been improperly stored or transported is more likely to contain damaging debris that could make its way through the fuel lines and to the injectors, ruining them.
Deffective Fuel Pump
Another reason fuel might not be getting to the engine is a bad fuel pump. Most gasoline from chain service stations is perfectly clean and properly stored, so bad fuel injectors aren't often the problem. However, you're more likely to have a defective fuel pump. If the fuel pump in your car goes bad, gas won't flow from the tank to the engine, and it won't be able to run on its own. Therefore, we'll recommend that you have the pump replaced.
Bad Spark Plugs
If the engine holds compression well, and the fuel system is working correctly, but it still won't start, that tells us that your car's spark plugs may not be working. This is because the spark plugs ignite the air/fuel mixture inside the engine's cylinders. It's the resulting explosion that powers your car.
Modern spark plugs can last 100,000 miles or more before going bad and needing to be replaced, but they can go bad earlier than that for various reasons: If the engine experiences too much carbon buildup, this can foul your spark plugs. Or, if oil leaks into the engine, it can coat the spark plugs and prevent them from working. The problem may also be with one of the components, like the computer or the ignition coils, that supply power to the spark plugs.
Bad Crankshaft Position Sensor
Not only does the engine in your car need a spark to begin combustion, but that spark has to take place at the exact moment. Too late or too early, the air/fuel mixture won't entirely combust, reducing performance and potentially failing to start the engine altogether.
One of the reasons your spark plugs might be firing incorrectly is a faulty crankshaft position sensor. This sensor tells your engine's computer the position of all the valves and pistons at any given moment. The ECU then uses this information to determine when to fire the spark. If this sensor has gone bad, the ECU won't know when to fire the sparks, and the engine might not start.