When your engine cranks but fails to start, it usually means your engine is having trouble producing a spark, getting fuel, or creating compression.
But, what if, ignition, fuel, and compression were all checked and are all working good.
So, What can you do when your engine cranks but fails to start.
It was easy to find the problem in the old days when engines were very basic.
In today’s vehicles there are tons of sensor, relays, modules and computers.
Each one has to be working properly and be able to do its job.
Many of these components talk to each other sending information back and forth.
So, If one fails it can affect others making it even harder to find the real problem.
Computers in modern vehicles monitor many of these components and can set trouble codes when problems arise. So, Your first check is to confirm any engine codes.
Faults in other systems, not just ignition, fuel, or compression problems, can stop your engine from starting.
A system component itself may be faulty, or there may be a problem with its wire connector or harness.
Sometimes you will need to dig a little deeper in your diagnostic testing to find the problem.
Other things to check that may be causing your engine cranks but fails to start problem.
Fuses – Relays
Checking fuses and relays is easy to do and can be done in just a few minutes using a test light.
Fuses and relays fatigue causing them to blow which will cut electrical current to crucial components. It is also possible to cause a engine cranks but fails to start issue.
So, The power center is located in the engine compartment. It is usually a large rectangular plastic box with a removable cover. If you can’t find it, refer to your vehicle owner’s manual for its location.
Alarm – Security System
When cranking the engine over does the security light flash?
Each manufacturer disables the engine in different ways when in security mode.
Occasionally the system will become confused due to a glitch or procedural error meaning the alarm system must be reset.
As a result, Your engine cranks but fails to start.
The exhaust gas recirculation (EGR) valve introduces a measured amount of exhaust gases into the intake manifold to get re-burned.
This helps lower engine temperature and harmful emissions.
But the valve can fail and stick either open or closed.
When the valve sticks open it may prevent your engine from starting. Other symptoms of a stuck-open EGR valve include rough idle and stalling.
Cold Start Injector
Some vehicle models use a cold-start injector. It operates as a regular injector, but only works when the engine is cold.
The injector may have its own thermo switch or may be commanded by the system control module.
If either the switch or the computer circuit fails, you may have a hard time starting the engine when cold.
The Manifold Absolute Pressure (MAP) sensor is used by the Powertrain Control Module (PCM) for engine load input.
The PCM uses this input, as well as others, to calculate the correct amount of fuel to inject into the cylinders. The manifold absolute pressure (MAP) sensor compares the barometric (atmospheric) pressure to the intake manifold vacuum. When the sensor fails, it can prevent your engine from starting.
The mass air flow (MAF) sensor tells the computer the amount (the density) of the air entering the engine.
A common MAF problem is dirt or foreign matter blocking the sensing element, preventing the sensor from working.
Or the sensor itself may fail after miles of service.
You may be able to clean and test the sensor at home.
The computer uses the engine coolant temperature (ECT) sensor to know how much fuel the engine needs.
Also, When to enter closed loop operation (that is, when the engine has reached operating temperature). A bad ECT sensor can upset ignition timing, or the operation of the transmission or cooling fan.
Canister Vent Valve
The canister vent valve is part of the evaporative emissions control (EVAP) system.
The EVAP system temporarily stores harmful fuel vapors into a canister to prevent their release into the atmosphere.
When conditions are appropriate, the computer routes the fuel vapors out of the canister through a canister vent valve and into the intake manifold for burning. A faulty valve, though, can prevent the engine from starting.
The throttle position sensor (TPS) monitors the position of the throttle valve.
It sends a voltage signal to the computer.
The computer uses this information to regulate the air-fuel mixture according to engine needs.
On some vehicle models, a worn out, failing or bad TPS will prevent your engine from starting at all.
So, Vacuum leaks are not uncommon, and they are the source of many engine performance problems. Depending on where the fault is located, vacuum leaks can be hard to find. But, Major vacuum leaks that can make the engine hard to start may happen in the:
- Power booster vacuum hose
- EGR valve
- Blown head
- Leaking intake manifold gasket
If you have an old vehicle model with a carburetor, double check that the fuel level is properly adjusted. If the carburetor is flooded, you’ll probably perceive a strong fuel odor under the hood.
A little trick you can use is to fully depress the accelerator and try to start the engine. Finally, If the engine doesn’t start, wait for a few minutes and try again.