Nine Common Reasons Why Your Engine May Start Then Stop
You’re driving along, and everything seems to be going just fine. But then, out of nowhere, your engine starts making a strange noise and eventually stalls out. You pull over to the side of the road, and now you’re wondering what went wrong.
It’s never fun when your car engine suddenly shuts down for no apparent reason. But before you start panicking, take a deep breath and try to diagnose the issue. There are a number of reasons why your engine may start then stop, and some are more serious than others. Here are 9 of the most common reasons:
NO.1 AIR INTAKE SYSTEM/VACUUM SYSTEM – LEAKS
What is AIR INTAKE? Air intake systems bring air from outside the car into the engine’s intake manifold, where it is mixed with fuel from the gas tank.
4 Symptoms of Air Intake Failure:
1.)|Reduced engine performance – A blocked air filter or throttle body will often result in a loss of power in your car’s engine. This may also be accompanied by increased fuel consumption and exhaust emissions.
2.)|Check engine light – If not enough air is entering your engine, the mass airflow sensor will detect the change and the check engine light may turn on.
3.)|Misfiring engine – A blocked air intake can lead to overly rich air/fuel mixture. This can foul / flood the spark plugs and cause your engine to misfire.
4.)|Rough idling – A blocked air intake system can lead to your car idling loudly, erratically or with higher RPM. This can also be caused by damaged/faulty engine sensors.
10 Signs Your Engine Has a Vacuum Leak
1.)|Reduced Fuel Economy
You might observe a fuel injector vacuum leak manifesting through reduced fuel economy. This issue occurs when the air/fuel ratio is imbalanced, and the fuel doesn’t burn properly, mainly owing to too much air intake. Poor fuel utilization is one of the consequences of a malfunctioning vacuum pump and connected tubes, and consumption might increase as a result. The problems arise due to latency in the discharge of exhaust gases from the combustion chamber. Also, gas buildup results in inefficient fuel combustion.
During idle, your automobile engine is most susceptible to malfunctions. As a result, it’s unsurprising that rough idle is among the most severe vacuum leak indicators. This is primarily due to your throttle body’s attempt to maintain a constant idle speed by opening and shutting the throttle valve. If there’s a significant vacuum leak, your throttle body would have difficulty controlling it, resulting in unusual idling sensations. It might be that the air/fuel ratio is becoming inadequate due to a vacuum leak.
3.)|Excessive Idle RPM
While idling, vacuum pressure exists inside an intake manifold since the throttle body prevents your engine speed from revving higher. Whenever you suffer a vacuum leak, this allows more air into your engine, which causes it to rev higher. That’s why, in most circumstances, a higher engine idle RPM is among the most typical indicators of a vacuum leak.
Exhaust gases from an automobile are often an indication of an issue. You might detect unusual black or white smoke, with the latter being more prevalent when vacuum leaks occur due to an insufficient air/fuel balance resulting in incomplete combustion. This results in an accumulation of exhaust gases that are visible in black.
A vacuum leak usually results in jerky or sluggish acceleration since the engine receives the incorrect air/fuel ratio due to unquantified air reaching or exiting the engine. Typically, a vacuum leak leads to a relatively lean mixture, resulting in delayed acceleration. You can sense the engine attempting to accelerate but being held back by something. Several more factors might contribute to poor acceleration, so always conduct a thorough diagnosis before replacing any components.
6.)|Misfires and Backfires
Whenever there’s a vacuum leak within your engine, it frequently begins to backfire and misfire. The air/fuel ratio might sometimes become so lean that it can’t effectively ignite the cylinders. It often results in misfire fault codes, such as the P0300. Once your vehicle’s engine misfires on a single occasion, it’s generally due to a vacuum leak somewhere in the intake manifold gasket. When you get misfires on all of your cylinders, a vacuum leak somewhere near your intake manifold might be the cause.
7.)|Hard To Press Brake Pads
As previously stated, the vacuum unit regulates your brake system, particularly in large diesel engines. Once the vacuum pump malfunctions, one of the signs is that your brake pad becomes challenging to press. The vacuum created by your pump contributes to producing the necessary pressure for you to start braking.
8.)|Engine High Pitch Noise
Damaged vacuum hoses usually cause a high pitch noise because your engine constantly draws air into the leak, creating noise. Assuming this is the issue, you are fortunate since high-pitched noise makes it much simpler to spot a vacuum leak. Simply listen to determine the source of the noise.
9.)|Check Engine Light
While driving your automobile, the engine control unit (ECU) constantly monitors and regulates all of the vehicle’s sensors. Once one of such sensors transmits incorrect data to your ECU, its check engine light will illuminate. Vacuum leaks frequently trigger the check engine light and a fault code stored in your ECU memory indicating that the ECU detected a lean mixture.
10.)|Total Engine Failure
Apart from the mentioned symptoms, there are various additional engine problems that you might experience. The difficulties may manifest as rough idling, throttle troubles, or an abnormally high idling speed. Additionally, there is the distinct car vacuum leak sound, like hissing, which you’ll hear once you start your vehicle if it’s more severe. Keep an eye out for potential engine blow-by to put your assessment one step forward.
2.) IDLE AIR CONTROL (IAC) VALVE
What is IDLE AIR CONTROL (IAC) VALVE? Idle air control actuator or idle air control valve is a device commonly used in fuel-injected vehicles to control the engine’s idling rotational speed. In carburetted vehicles a similar device known as an idle speed control actuator is used.
The idle air control valve is programmed to regulate and maintain the engine idle speed at a constant rate. If the valve fails or has any issues it can cause the idle speed to be thrown off. This may result in an unusually high or low idle speed, or in some cases a surging idle speed that repeatedly climbs and falls.
7 Symptoms of an IAC Valve Problem
1.)|Irregular Idle Speed
So, one of the most common symptoms associated with a problematic idle air control valve (IAC) is, irregular idle speed. The (IAC) is programmed, to regulate and maintain the engine idle speed, at a constant rate. So, if the valve fails or has any issues, it can cause the idle speed to be thrown off. This may result in an unusually high or low idle speed. And, in some cases, a surging idle speed, that repeatedly climbs and falls.
2.)|Check Engine Light Illuminated
Another symptom of a potential issue with the idle air control valve (IAC) is, an illuminated Check Engine Light. As a result, of the engine control module detecting an issue with the idle air control valve circuit or signal.
Another more serious symptom of an issue with the (IAC) is engine stalling. If the idle air control valve (IAC) fails completely, it may leave the vehicle, without a source of air. This may result in the engine stalling while operating. And, in some cases, may result in an engine that will not idle at all.
4.)|Engine Hard Start
If an engine isn’t getting enough air, it might not start or will have difficulty starting. This could indicate an issue with the idle air control valve.
When the source of air into the engine is inconsistent, it will create a glugging, hesitating, and revving and dying sound. You’ll know something is up.
6.)|Car Starts, Then Dies
If the valve works occasionally, or it only works in certain parts of its cycle, the car might be able to start before it starves of air and dies.
If the engine doesn’t have enough air, the air-to-fuel mixture ratio is off, and some fuel might be left after the spark. This fuel then makes its way through the system and could cause a backfire.
3.) FUEL PRESSURE/FUEL PRESSURE REGULATOR
What is FUEL PRESSURE REGULATOR? A fuel pressure regulator helps maintain the fuel pressure in the Electronic Fuel Injection System. If the system needs more fuel pressure, the fuel pressure regulator allows more fuel to go to the engine. This is important because that is how the fuel gets to the injectors. Blocking the pass-through to the fuel tank off completely, the fuel pump will try to force too much fuel into the injectors which will cause them to fail and you will end up needing another auto repair service.
12 Signs That Your Fuel Pressure Regulator May Be Failing
1.)|Loss in Acceleration
The fuel regulator controls the fuel pressure, and if the fuel pressure is incorrect, the engine will have too low or too high fuel pressure. An incorrect fuel pressure causes the air-fuel ratio in your car engine to be either too rich or too lean, depending on the pressure.
The engine needs a correct air-fuel mixture to function properly. Both too lean and too rich air-fuel mixture will cause a drop in acceleration. Therefore, if your car feels slower than before, it could be a problem with the fuel pressure regulator.
2.)|Check Engine Light
Almost all modern cars use a full-time monitoring system to monitor the car engine’s sensors constantly. If one of these sensors fails, a trouble code will be stored in the engine control module’s trouble code memory, and if this happens repeatedly, the check engine light will appear on your dashboard.
Most car models have a fuel pressure sensor that controls the fuel pressure in the fuel rail. If the fuel regulator is broken and the fuel pressure becomes too high or too low – the check engine light will appear on your dashboard.
Another common symptom when the fuel pressure regulator goes bad is fuel leakage, which causes performance problems and leads to bad smells. A fuel leak occurs when the fuel regulator diaphragm or outer seal is damaged and broken. Fuel leaks are also very dangerous as they can cause your car to catch fire and should therefore be attended to immediately.
4.)|Black Smoke from the Exhaust Pipe
Many people think that only diesel engines will get black smoke from the exhaust, but it can actually happen to gasoline engines also if the air-fuel mixture is too rich. As we discussed earlier, a bad fuel pressure regulator can cause a rich air-fuel mixture. This means that black smoke from the exhaust can be a sign of a bad fuel pressure regulator.
Black smoke coming out of your car’s exhaust can have various other causes, but if you see black or gray color exhaust smoke and also notice other symptoms mentioned in this article, the problem is very likely with the fuel regulator.
5.)|Spark Plug Covered with Black Debris
If your engine is running too rich, caused by a faulty fuel pressure regulator, there is a significant risk of your combustion chamber becoming full of soot.
If you are about to change the spark plugs and notice that the end of the spark plugs are completely black and full of soot, it is a sign that your engine is running rich. It is also a sign that the fuel pressure regulator is bad and you may need to replace both the fuel pressure regulator and the spark plugs.
A faulty fuel pressure regulator will cause excess fuel to flow through the combustion chamber, and the engine will not be able to burn it all and therefore will overfill the exhaust system with fuel.
The fuel will then flow into a hot exhaust system, which will then ignite and cause an explosion of all the unburnt fuel in the exhaust system. This is quite dangerous and can cause your exhaust pipe to explode and your car to catch fire. Therefore, it is important to get it fixed as soon as possible.
7.)|Vacuum Hose filled with gasoline
A defective fuel pressure regulator diaphragm can cause fuel pressure to enter the vacuum system instead of the engine. This will cause the vacuum hoses and the intake manifold to become filled with gasoline.
To check this, remove the vacuum hose connection to the fuel pressure regulator and check for gasoline in the line. If so, you most likely have a faulty fuel pressure regulator.
8.)|Gasoline Smell from the Dipstick
As we discussed earlier, a bad fuel pressure regulator can cause the engine to run rich. Also, an engine that runs rich for a long time will cause unburned fuel to flow into the oil pan and fill it with gasoline.
To check this, you have to lift the engine oil dipstick and check the oil level, and if you can smell or can see gasoline on the dipstick, it can mean that your fuel pressure regulator has a problem.
9.)|Drop in Mileage
Improper fuel pressure can not only cause a rich mixture, but it can also cause a lean air-fuel mixture. While you may think that a drop in mileage might be helpful, it can actually seriously damage your car engine over time.
A lean mixture will often cause your car to drop in acceleration as well, but if anything, the only symptom you may notice is a drop in mileage.
10.)|Engine Won’t Start
Here’s the most apparent symptom – an engine that won’t turn over.
The fuel regulator is in charge of providing the right amount of fuel for any situation, including starting the engine in the first place. If there is not enough, it will not be able to fire up.
You may be able to get the engine started initially, but eventually, it will fail altogether. Many things can keep a car from starting, so be sure to look for other symptoms on this list to be sure.
11.)|Excessive Fuel Pump Noise
The fuel pump makes noise, but it should never reach the point where it’s annoying. If yours has started making a “whirring” sound, it might be going out. However, the noise may also be caused by a faulty fuel pressure regulator.
The sound should be most noticeable when the engine is under stress, such as while accelerating, climbing a hill, or towing a trailer.
12.)|Fuel Drips Out Of The Tailpipe
Like gasoline in the vacuum hose, a bad fuel regulator may be the culprit if fuel drips out of your tailpipe. The fuel regular has several seals, which can leak when worn or damaged. If a fuel leak is present, it means your engine will not get enough, which will display as the engine having reduced performance.
4.) FUEL LINES – LEAKS/DAMAGE/BLOCKAGE
If you can’t start your vehicle, or your vehicle’s engine is sputtering or dying, you may be having issues with your fuel line. Tow your vehicle to a mechanic if you need to find out for sure. However, you should be able to narrow down the cause of your problem. Here are signs of a faulty or clogged fuel line, although the problem could exist throughout your fueling system:
1.) Can’t Start The Engine
If your engine won’t turn over, you may have a clogged fuel line or a fuel line that’s punctured and leaking. Your fuel line brings fuel from your fuel tank to your engine, and when that fuel doesn’t make the journey, well, your vehicle simply won’t work.
2.) Smoking Engine
If you see smoke in your engine compartment, it is dangerous! Faulty fuel lines can cause fuel to spray or leak out, and fuel that comes into contact with a heat source may ignite. Smoke could be the result of a faulty fuel line. Do not leave your vehicle running if it is smoking. Stop, shut off your engine, and walk away from the vehicle.
3.) Engine Is Cutting Out
If your fuel line is blocked or leaking, your engine won’t get enough fuel, or it’ll get fuel in inconsistent spurts. That’ll cause engine sputtering or it may force your engine to cut out. Don’t run your engine if it is sputtering. A sputtering engine will likely damage itself. You’ll need to have your vehicle towed to a location where it can be repaired.
5.) THROTTLE POSITION (TP) SENSOR
What is THROTTLE POSITION SENSOR? A throttle position sensor is a sensor used to monitor the air intake of an engine. The sensor is usually located on the butterfly spindle/shaft, so that it can directly monitor the position of the throttle. More advanced forms of the sensor are also used.
1.) Check Engine Warning Light
One of the first bad throttle position sensor symptoms is the Check Engine Light will flash on your dashboard to warn you when any sensor goes bad. If the Check Engine Light is turned on, pay attention to any other strange signals and troubleshoot as soon as possible before the issue gets worse.
2.) Poor Fuel Economy
As mentioned above, due to the engine’s inefficiency, poor fuel economy will be one of the inevitable bad throttle position sensor symptoms. The throttle position sensor works alongside other sensors to ensure the engine gets everything it needs to run smoothly.
When these sensors start to go bad, your car’s computer receives incorrect data, leading to your engine getting incorrect inputs. Different parts try to overcompensate for these deviations.
For instance, if the engine is receiving more air than it needs, the computer will compensate by injecting extra fuel to rebalance the air-fuel mixture. Therefore, in most cases when your sensor goes bad, your car will be noticeably consuming more fuel than usual.
3.) Engine Rough Idling Or Sudden Stalling
Faulty throttle position sensors can cause rough idling due to fluctuating airflow. If you see your car misfiring, idling rough, or stalling out while you drive, it is highly likely that you’re having a faulty throttle position sensor.
4.) Startup and Acceleration Issues
Also due to fluctuating airflow, a bad throttle position sensor may cause all sorts of power issues. Your engine may start up but it will have little to no power, runs briefly, but then dies out.
Otherwise, it can also cause your car to have spontaneous surges during accelerations for no apparent reasons, or cause weaker accelerations than usual.
5.) Abrupt bucking or jerking
The throttle position sensor sometimes fails in a way that causes the signal sent to the engine’s computer to be sporadic. The effect will be similar to when you are quickly applying and releasing the gas pedal.
6.) Difficulty In Switching Gears
If the throttle position sensor fails it can cause automatic transmission shifting problems. The throttle position sensor is important for proper automatic transmission control because it immediately establishes the driver’s intent, and transfers this information to the Transmission Control Module.
Without such correct and timely transfer of data, you will experience delay and/or difficulty in switching gears.
7.) Your car goes into limp-home mode
In some models, a failing or faulty throttle position sensor can cause the engine to go into “limp-home mode”. In this situation, you will experience reduced engine power, and you may be stuck in a higher gear.
This is a safety feature designed to get you off the highway and allow you to drive a few extra miles to the nearest repair shop. Once this happens, do not drive any more than needed and get repairs immediately.
6.) MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
What is Manifold Absolute Pressure Sensor? The Manifold Absolute Pressure Sensor (MAP sensor) works with intake air pressure to define proper air and fuel quantities required for the ignition cylinders. The MAP sensor measures the vacuum of the intake manifold, which fluctuates according to engine load, relative to the barometric pressure.
1.) Check Engine Light
The engine control unit constantly monitors all the sensors in your car engine while you drive the car. If one of these sensors’ values is out of the specified range – the check engine light will show up.
Therefore, if your MAP sensor sends wrong information to the engine control unit, the check engine light will appear on your dashboard.
2.) Lean Air-fuel Mixture
The MAP sensor’s primary purpose is to measure the air pressure in the intake manifold to calculate the right air-fuel mixture for your engine. If the sensor is bad, it may cause your engine to get a too lean air-fuel mixture.
Lean fuel mixture can cause many strange symptoms in your engine, which you will find further down in this list.
3.) Rich Air-fuel Mixture
The same thing applies the other way around also. If the MAP sensor is bad, it can also send a faulty signal, which will cause the engine control unit to inject too much fuel into the car engine.
A rich air-fuel mixture will not only cause your fuel consumption to go up – but it will also cause performance problems.
4.) Stalling or Rough Idle
If your air-fuel mixture is too rich or too lean caused by a faulty MAP sensor, you may notice problems at the engine’s idle. When the engine is running at idle, it is very sensitive, and therefore you may first notice a faulty air-fuel mixture at idle.
Many other faulty parts can also cause this, so it should be diagnosed properly before you replace the MAP sensor.
Misfires occur when the combustion inside the engine cylinder fails. This can happen due to a wrong air-fuel mixture or a bad spark. A MAP sensor may actually cause the air-fuel mixture to become so bad that you may notice misfires.
You can often recognize misfires by listening to your engine. If you can hear small bumps or if it doesn’t sound like it usually sounds – it may be caused by misfires.
6.) Increased Emission Level
If the manifold absolute pressure sensor (MAP) is damaged, it can send an incorrect signal to the powertrain control module (PCM), indicating a high or low engine load.
To have a good emission level in your car, the air-fuel mixture needs to be perfect. Even a slight error with the MAP sensor may cause the fuel mixture to disturb the emission levels.
7.) Bad Engine Performance
As we talked about earlier, a faulty fuel mixture will cause the engine performance to drop. A lean mixture usually causes decreased engine performance, but it can absolutely be caused by a too rich mixture also.
Bad engine performance can also be caused by misfires caused by a bad MAP sensor, as discussed earlier in the article.
8. ) Backfires
Backfires happen when the fuel going through your engine is not combusted properly. When the fuel is not ignited in the combustion chamber, it may end in the exhaust pipe. As you may suspect, the exhaust pipe becomes really hot, and this can ignite the air-fuel mixture there.
This will cause loud bangs coming from the exhaust system, and this can actually cause your mufflers, etc., to explode. It can also cause your car to catch on fire if you are unlucky.
9.) Hard Starting Condition
A faulty MAP sensor also causes problems when starting the car. The car’s trip computer uses the MAP sensor to determine the air pressure before starting the engine.
The engine is very sensitive for the right air-fuel mixture at the starting moment, and therefore, a faulty reading can cause a too small amount of fuel to be delivered to the engine, and as a result, the engine may not start at all.
10.) Changed fuel consumption
This is most probably the most understandable if you read everything above in the article. A faulty air-fuel mixture caused by a bad MAP sensor will, of course, also cause the fuel consumption to get changed.
If you notice that your car requires less or more fuel than before, it can absolutely be caused by a faulty MAP sensor.
7.) CONDITION OF FUEL/FUEL FILTER
If the fuel filter is clogged and not replaced promptly, your car may not start at all. rough idle or misfire A clogged fuel filter may prevent the engine from receiving enough fuel.
The most common symptom of a clogged fuel filter is difficulty starting the car, as it depletes the oil supply to the engine. Although a dirty fuel filter causes ignition problems, a completely clogged filter will fail and the engine will not start.
8.) ENGINE MANAGEMENT SYSTEM – CONNECTIONS/WIRING/RELAYS
A no-power condition is another sign of a faulty ignition relay. If the relay fails, it will cut power to the fuel pump and ignition system, resulting in no power and the car not starting.
electrical or wiring problems. All of the non-starting cars we saw had an electrical problem or a wiring issue. These included issues with the fuse box, with battery cables, or with the body control unit.
9.) ENGINE CONTROL MODULE (ECM)
If the ECM malfunction is severe, the vehicle may not be able to start at all. A complete ECM failure means the vehicle has no engine management. As a result, the car cannot start because it lacks core inputs from the computer.
These are all the possible reasons why your car is running and then suddenly stops. I hope this simple tutorial will help with this car problem. Thank you very much! Compiled and researched with love by Erwin C. Salarda