When your engine turns over but will not start, it usually means your engine is having trouble with spark, fuel, compression or timing.
But, What do you do if all that checks out ok and still the engine will not start.
The source of the problem could also be a mechanical fault, or faulty components in other systems.
No start when the engine turns over can be a number of issues but you need to start somewhere.
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.
When trying to find out why your engine will not start, keep in mind other possibilities. What should you check ?
First, Check for a blown fuse that may be preventing a circuit from working properly, like the computer system.
What Can Cause A No Start Condition
Faults in other systems, not just ignition, fuel, compression and timing, can prevent your engine from starting. A system component itself may be faulty, or there may be a problem with its wire connector or harness.
You may need to expand your diagnostic procedure to the other systems listed below:
Exhaust Gas Recirculation Valve (EGR)
The EGR 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
One of the first symptoms typically associated with a bad cold start injector is a problem starting the vehicle.
The cold start injector is there to enrich the fuel mixture of the vehicle during low temperature conditions.
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 no start condition.
Manifold Absolute Pressure Sensor (MAP)
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.
Mass Air Flow Sensor (MAF)
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.
Engine Coolant Temperature Sensor (ECT)
The computer uses the engine coolant temperature (ECT) sensor to know how much fuel the engine needs and when to enter closed loop operation (that is, when the engine has reached operating temperature). Depending on your particular model, a bad ECT sensor can upset ignition timing, or the operation of the transmission or cooling fan.
Evaporative Emissions Control System (EVAP) 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.
Throttle Position Sensor (TPS)
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, including will not start. Depending on where the fault is located, vacuum leaks can be hard to find.
But mayor vacuum leaks that can make the engine hard to start may happen in the power booster vacuum hose, EGR valve, another main vacuum hose or a blown head or intake manifold gasket.
Carburetor – If You Have One
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. If the engine doesn’t start, wait for a few minutes and try again.
When your engine turns over but fails to start, it can be difficult to fix if you don’t know where to begin troubleshooting.
This guide not only tells you where to start but helps you build your diagnostic strategy.
And reminds you of some simple but easy to forget places to look into. So most of the time, using just this guide you’ll be able to zero in on the problem.
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