How To Troubleshoot Your Car’s Stalling Engine

July 13th, 2010 |

Engine stalls can occur for many reasons, including failing sensors, compression issues, and problems within the ignition system. Unfortunately, today’s vehicles are designed with such a high level of complexity that troubleshooting the issue is difficult. There are many parts that can potentially contribute to the stall.

With this in mind, we’ll explore your car’s engine, ignition system, and other components. We’ll approach them with the goal of understanding which parts can play key roles in preventing your vehicle’s engine from running. The circumstances under which stalling occurs will, in part, dictate the components to check. This will become clearer below.

Check For Sufficient Fuel

Your engine obviously needs fuel in order to operate. But even if it receives fuel, the volume may be insufficient to keep it running. If your engine stalls while you’re driving, and the reason is due to insufficient fuel, the fuel pump is likely failing.

The pump is responsible for creating pressure in the line. If it fails, the pressure will dissipate, and your engine will receive too little fuel. This causes a stall. You will be unable to restart your car.

If your engine stalls when you try to cold start it, the problem is still likely to be too little fuel. But in this case, the fuel pump is unlikely to be the culprit. Instead, it may be a failing airflow sensor (described in more detail below) that is delivering bad data to your vehicle’s powertrain control module (PCM). This might be leaning out the air-fuel mixture in the cylinders.

Look For Ignition System Problems

There are several components that comprise your vehicle’s ignition system. These include the ignition coil, distributor, distributor cap, rotor, and spark plugs. These parts work together to perform a primary job: to ignite the air-fuel mixture in your engine’s cylinders. It accomplishes this task by transferring an electrical current from your ignition coil to your spark plugs. The transfer of the current depends on each part along the way.

If any component in your ignition system fails – or even falters – the current will be interrupted. This will cause your engine to stall. Related to this issue is the operation of your crankshaft position sensor (CPS). This is a sensor located in your engine that monitors your crankshaft. It sends the data to the PCM, which uses it to control ignition timing. If the CPS fails (due to wear and tear, or prolonged exposure to high temperatures), your PCM may lower your car’s idle, causing your engine to stall.

Are Your Car’s Sensors Failing?

Your vehicle is equipped with several sensors that deliver important data to your PCM. The PCM acts upon this data to ensure your engine runs efficiently. If any of the sensors malfunction, the computer will receive compromised data, or none at all. As you might suspect, this can lead to problems with your engine’s performance.

For example, the mass airflow sensor (MAS) is tasked with monitoring the amount of air that flows into your car’s engine. It relays this information to the PCM, which makes changes in the amount of fuel sent to the cylinders. If the sensor become contaminated, or it fails, the PCM may lean out the air-fuel mix.

The manifold absolute pressure (MAP) sensor also plays a key role. It monitors the load placed on your engine and sends the data to the PCM. The computer uses the information to optimize ignition timing. As with the MAS, a failing MAP can cause the PCM to lean out the air-fuel mix, and thus cause a stall.

Other factors that can cause stalling include worn spark plugs, vacuum leaks, a faulty exhaust valve, and even a failing coolant sensor. In most cases, troubleshooting the problem requires the expertise of a trained mechanic.

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