Last Updated on September 24, 2021
Anyone who owns a vehicle has likely experienced the frustrating problem of a car that cranks but doesn’t start, even after repeatedly turning the key in the ignition. However, don’t let desperation keep you from logically figuring out why your vehicle cranks but won’t start normally.
Related: What to Do if Your Car Breaks Down
Reasons a Car Cranks But Won’t Turn Over
Cranking the car is engaging the starter to energize the engine. The starter causes the flywheel to turn which rotates the crankshaft when all is working correctly. Sometimes this process is interrupted when there is a hitch in the system, and the car engine won’t continue to run after it “turns over” or cranks.
For the engine to start normally, it requires sufficient fuel pressure, an appropriately timed spark and normal compression. When it doesn’t start, the problem usually lies with one of these systems though the starter system can also be the culprit. Below are some common causes of an engine that cranks but doesn’t start and some troubleshooting tips to identify the cause.
#1 – Spark Problems
Lack of spark may occur due to a damaged ignition module, a faulty crank position sensor, a flooded engine (sometimes happens in older or high-mileage cars), bad spark plugs, or a problem in the ignition circuit, such as the wiring, security system (the fuel flow may have been shut off to prevent theft or the chip in the key could be faulty), or a malfunctioning ignition switch.
An inappropriately timed spark can occur if there’s an issue with the timing system. This can be difficult to diagnose, but a timing light is a useful tool to check that all the cylinders are firing exactly when they are supposed to.
To determine if there is a problem with the spark, visually check the distributor cap (if your vehicle has one) and the spark plug wires, as these may degrade with age. A spark tester should be used to check for a proper arc from each spark plug wire or coil.
If you suspect the engine may be flooded after repeated attempts to start the car, remove the spark plugs and let them dry, then replace them and try again.
Related: Symptoms of a Hydrolocked Engine
#2 – Lack of Fuel Flow
Problems with fuel flow may be due to a damaged fuse for the fuel pump, a bad fuel pump, contaminated or incorrect fuel in the tank, a faulty or clogged fuel filter or injector, or simply an empty fuel tank (the fuel gauge is not always accurate).
Having the appropriate fuel pressure is important for your car engine to start or run, especially for fuel-injected engines. Listen to hear the fuel pump buzz for a few seconds as you turn the ignition to the “on” position.
If no buzz is heard from inside the car or back by the fuel tank, the pump may be dead and fuel is not reaching the engine at all.
Note that some fuel pumps only flow while the car is cranking so some cars don’t have an audible buzz. Consult the internet or your owner’s manual for more information for your specific model.
If you do hear the buzz of the fuel pump, you can try putting a flathead screwdriver on top of each injector (with the handle next to your ear) while the car is cranking. If the injectors are firing, you will hear a faint ticking sound from each injector, transmitted by the shaft of the screwdriver.
Some cars have a safety feature called an inertia switch which shuts off the flow of fuel automatically after an impact. If your vehicle recently sustained an impact, check your owner’s manual to see if this feature is present in your vehicle and learn how to manually switch it to allow fuel to flow again.
#3 – Low compression
Each cylinder needs compression for correct engine function. The compression ratio compares the maximum cylinder volume to the minimum cylinder volume during each stroke of the piston. If one or more cylinders have low compression, air from the combustion cycle leaks past the piston rings which limits the amount of work that cylinder can do to spin the crankshaft.
Compression problems can be caused by a broken or loose timing belt or chain or a snapped overhead camshaft. An overheated engine is another severe problem that can prevent your car from starting.
Try using a compression gauge or tester to see if you have a problem with the compression in your car. If so, a leak down test is a secondary test to check for leaks in the cylinder. A professional mechanic can perform these tests and examine the cylinders if you don’t feel comfortable checking yourself.
#4 – Power Supply Problems
Another possible problem is a weak starter motor that uses a lot of amps to crank the engine, then doesn’t have much juice left to switch on the fuel injectors and ignition system. In this case, you will probably notice that the starter makes an unusual noise when you attempt to crank the engine or it doesn’t turn over at all.
Weak or corroded battery cables or a dying battery can contribute to the problem as well. Check the voltage of the battery with a multimeter while cranking the engine. It should show over 10 volts.
Check for blown fuses by visually removing and inspecting the wiring of each fuse when the car is shut off. If they appear to be in good condition, put them back in then try turning the car ignition into the “on” position and using a test light to check each fuse for electrical current flow. Replace any damaged fuses with new ones from an auto supply store.
If the engine cranks but won’t start, turn the car off and remove the air inlet tube attached to the throttle body. Then spray a small quantity of starting fluid into the engine after gently pushing the throttle open. With that done, try cranking the engine once again.
If the engine starts but dies after a few seconds, this means that it has no fuel but the spark and compression are okay. However, if the engine does not start, it almost certainly lacks spark.
Avoid repeatedly cranking the car engine to try to make it start, as this can wear out the starter or drain the battery.
If you must try multiple times, wait several minutes for every 15 seconds of cranking performed to allow the starter to cool down. It shouldn’t take more than a couple seconds per attempt to know if you’ve resolved the issue.
Checking sensors and actuators for problems is critical, as modern cars have a variety of electrical components that can cause failure in the engine starting process.
The best way to do this is to check the car computer for codes (faults in the electrical system) with a scan tool that can be found at most auto supply stores. Most of these problems will also cause the check engine light to illuminate, but not all of them.