Engine Turns Over - But, Will Not Start

So, 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 those things check out good, and the engine still won’t start.

The source of the problem could be, a mechanical fault, or a faulty component in other systems.

Consequently, a no start condition, when the engine turns over, can be a number of issues. But, you need to start somewhere, so lets dive in.

So, the computer in modern vehicles, monitors and controls, a good number of sensors and actuators. Firstly, 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. And, that can guide you in your diagnosis. However, when trying to find out why your engine will not start, keep in mind other possibilities.

So, what should you check ?

Firstly, check for a blown fuse, that may be preventing a circuit from working properly, like the computer system.

Blown Fuse, But, Engine Turns Over — Blown Fuse

What Can Cause, A No Start Condition

Faults in other systems, not just ignition, fuel, compression and timing, can prevent your engine from starting. And, a system component itself may be faulty, or there may be a problem with, its wire connector or harness.

System Components, Sensors And Actuators

In addition, you may need to, expand your diagnostic procedure, to other systems listed below:

Exhaust Gas Recirculation (EGR) Valve

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. Consequently, during low temperature conditions. However, the injector may have its own thermo switch. And, may be commanded by, the system control module. As a result, 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. Consequently, when the sensor fails, it can prevent your engine from starting.

Mass Air Flow (MAF) Sensor

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. As a result, preventing the sensor from working. However, the sensor itself, may fail after miles of service.

Engine Coolant Temperature (ECT) Sensor

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). Therefore, a bad (ECT) sensor, can upset ignition timing and 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. As a result, preventing their release, into the atmosphere. The computer routes the fuel vapors out of the canister, through a vent valve and into the intake manifold. That’s why, a faulty valve, can prevent the engine from starting.

Throttle Position (TPS) Sensor

The throttle position sensor (TPS), monitors the position of the throttle valve. So, it sends a voltage signal to the computer. Then, the computer uses this information, to regulate the air-fuel mixture, according to engine needs. And, on some vehicle models, a worn out, failing or bad (TPS), will prevent your engine from starting.

Vacuum Leaks

So, vacuum leaks are not uncommon. And, they are the source, of many engine performance problems. And, also include, a engine that will not start. In addition, depending on where the fault is located, vacuum leaks can be hard to find.

Furthermore, mayor vacuum leaks, that can make the engine hard to start, may also happen in the:

Power booster vacuum hose.
(EGR) valve.
Main vacuum hose.
Blown head.
Intake manifold gasket leak.

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. Then, if the engine doesn’t start, wait for a few minutes and try again.

Conclusion

So, 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.

Thank You !