When your engine turns over, but will not start, it can feel devastating.
Usually, the most common causes, are in the ignition or fuel system.
So, it could mean, your engine is having trouble, producing a spark, getting fuel, or even creating compression.
Consequently, what “engine turns over but will not start” doesn’t generally mean, is a problem with the starter. Because, if the engine cranks normally, you don’t have a starter problem.
The most common causes are usually, in the ignition or fuel system. However, the source may also be, a mechanical fault (for example, a leaking valve) or faulty components in other systems.
Whatever you do, avoid cranking the engine repeatedly, with the hope that the engine will fire up. You may drain your battery of power and damage the starter motor in the process. Instead, try to use the charge left in your battery to locate the fault.
When trying to find out why your car doesn’t want to start, keep in mind these possibilities:
Sensors and Engine Codes
The computer in modern vehicles monitors and controls, a good number of sensors and actuators. Scan your computer memory for trouble codes, before you do anything else. Even if the check engine light hasn’t come on; you may find a pending code, that can guide you in your diagnosis. False input or lack of input from sensors, like the crankshaft position sensor (CKP); or camshaft position sensor (CPS), can prevent the engine from starting. Also, a bad throttle position sensor (TPS), may cut off the spark to the cylinders.
If the engine cranks slowly, you may be dealing with, a discharged battery; loose or corroded battery terminals or starting system wires.
If the engine doesn’t crank or makes an unusual noise when cranking, you may have a starting system problem.
The car’s security system may have made an error; that disabled the fuel or ignition system or the chip in the key may have failed.
So, to troubleshoot, a built-in security system, consult your car owner’s manual. Also, check for a blown fuse, that may be preventing a circuit, from working properly. Consequently, effecting the fuel injection or computer system.
Finally, while it is a little on the unlikely side, check that you aren’t experiencing a compression issue. A leak down test could show low compression, exposing a failed head gasket or bent valve. Low or no pressure in all cylinders, would also be a reason that an engine won’t start. And, it’s often a sign of serious engine damage, like a broken timing belt/chain, camshaft, or other bottom end parts.
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