What can be more irritating than having a car that cranks but won’t start when you are in a hurry somewhere?
Not a lot of things actually.
Luckily even if it feels like a big problem, it can, in most cases, be a straightforward and easy problem to fix.
5 Causes of Car Engine Cranks but Won’t start
- Lack of fuel
- No spark
- Wrong ignition timing
- Soaked cylinder or spark plug
- Lack of compression
- Lack of electric power
These are the most common causes of why your car is cranking but won’t start.
Here is a much more detailed list of the 6 most common reasons why your engine cranks but won’t start.
Lack of fuel
The most common reason why your car won’t fire up is actually lack of fuel. Lack of fuel is usually caused by a clogged fuel filter, faulty fuel pump, or clogged injectors.
It can also be the MAF/MAP sensor that sends the wrong signal to the ECU to inject too little or way too much fuel into the engine.
Check the fuel pressure in the fuel rail with a fuel pressure gauge to ensure you have fuel pressure.
If you do not have any or too low fuel pressure, you should make sure that the fuel filter is not clogged and that the fuel pump starts when you crank the engine.
If your engine has no spark, you can crank the engine for how long you want, but it will never start. Remove a spark plug and put the threads against a grounded area on the engine. Crank the engine and make sure that you have spark.
If you do not have any spark, the most common problem is faulty ignition coil/s or a faulty crankshaft sensor. If you have an older car, you might have a problem with the single ignition coil or the distributor.
Wrong Ignition Timing
If your engine control units send out the spark to the ignition coil too early or too late, you might also have problems starting the car.
To see the ignition timing on an older engine with adjustable timing, you can use a strobe light to ensure it is within the range.
If you have a newer car without adjustable timing, you can get a faulty ignition timing from a faulty crankshaft or camshaft position sensor.
Soaked Cylinder & Spark plug
In some rare cases, the cylinder and spark plug can be soaked by fuel, making it impossible for the spark plug to ignite the air-fuel mixture.
If you suspect this – remove the spark plugs and dry them. Crank the engine for a while without spark plugs and then install everything back together again.
There is also a chance that your car engine has too low compression to start. This is not very common, though, because it is very doubtful that the engine compression suddenly got low on all cylinders.
Anyway, it can be good to make a compression test to ensure no problem with the compression.
Low compression can be caused by bad piston rings, valve seats, or a very wrong camshaft timing. Make sure that the camshaft timing is correct if you experience a very low compression.
Lack of electric power
If you have tested everything in this list, but the car is still not starting, there is a chance that the car engine has enough electricity to turn the engine around with the starter motor – but not enough for the rest of the ignition components to fire the engine up.
Charge your car battery for a night, replace it, or take power from another car to ensure that you do not lack power.
The easiest way to diagnose a car engine that cranks but won’t start is to remove the spark plug after you tried to start the car for a while to inspect it.
If the spark plug is wet – there is most likely a problem with the spark, ignition timing, or compression.
If the spark plug is dry – there is most likely a problem with the fuel supply.
Hi, I’m Magnus, the owner and the writer of Mechanic Base. I have been working with cars for 10 years, specialized in diagnostics and troubleshooting. I created this blog because I was tired of finding false information on the web while looking for repair information. I hope you enjoy my content!