10 Common Reasons Your Car Won’t Accelerate
Gas-powered cars use complex systems to run. Problems with the fuel or air supply, exhaust fumes, or anything in between can cause your car to be sluggish or not accelerate.
An internal combustion engine must have a specific ratio of air and fuel in each cylinder at the right time, which then ignites in a carefully timed manner.
These variables can change depending on what your car is doing at the time and the environment you’re driving in. A car at idle, for example, has different air/fuel requirements than a car accelerating rapidly to merge onto the freeway. Cold temperatures require more fuel because the air is more dense. The electronic control module (ECM) or electronic control unit (ECU) is the brain of the car.
Acceleration problems can be difficult to troubleshoot because there are many possible causes. We’ll cover 10 major categories below. Start troubleshooting the problems that are easiest and cheapest to repair/replace and work your way up from there. Some of these systems may require the help of a mechanic.
10 Most Common Reasons Why Your Car Won’t Accelerate
1) Emergency Brake Engaged/No Fuel Left
While these may seem obvious causes of slow acceleration, it’s important to make sure the emergency brake is disengaged and that the vehicle has enough gasoline. If one or both of these issues occur, your vehicle may accelerate slowly or even stall. This is rarely the case, but should be mentioned first before any further bug fixes are made.
2) Fuel Issues (Injectors)
If there is anything blocking the proper amount of fuel from entering the combustion chamber, acceleration issues can occur. The fuel filter is an often overlooked component, but a clogged or dirty fuel filter is a common culprit. Over time, fuel filters fill up with sediment and dirt from the fuel, so they need to be changed regularly.
Clogged or dirty fuel injectors can cause misfires and erratic spraying, disrupting the combustion process. In some cases, these can be cleaned by adding fuel additives to the gas tank.
A defective fuel pump can also cause poor fuel flow, in which case it will need to be replaced. Frequently driving on empty gas tanks can weaken the fuel pump over time. A faulty tank, the wrong octane rating, or contaminants in the fuel (such as dirt or water) can also cause poor acceleration. In this case, draining the tank and filling it with new fuel will solve the problem.
3) Spark or Timing Issues
A faulty ignition coil, distributor, or spark plug can also cause a misfire. Without a spark in the cylinder, there can be no detonation (and of course, a detonation at the right time is what ultimately powers the vehicle). A spark at the wrong time is useless and can even damage the engine. The ignition coil converts the low voltage from the battery into the high voltage needed for a spark to fill the gap at the spark plug. The distributor passes this voltage from the ignition coil to the spark plug itself. Most modern cars don’t use a distributor, so this isn’t even a potential problem.
4) Mechanical trouble (clutch)
Internal combustion engines have a lot of moving parts, so there are a lot of parts that can break or fail.
A misaligned timing belt or chain can cause the engine’s intake and exhaust valves to open at the wrong time. You may notice a lopey idle if this is the case. If the timing belt is too loose, the timing may not be correct.
A slipping clutch or low clutch fluid can lead to issues as the gearbox is unable to correctly engage with the engine. A slipping clutch will cause the engine speed (RPM) to increase quickly while your ground speed stays roughly constant. Leaving the exhaust gas recirculation (EGR) valve open will allow excess exhaust gases into the system and cause the sensor to fail. This will also reduce the amount of oxygen in the cylinders, reducing power. Note that a closed EGR valve will not affect performance unless the ECU puts the vehicle into limp mode.
A clogged or defective catalytic converter can cause excessive backpressure in the engine. A clogged catalytic converter can be very dangerous and can even cause a fire.
5) Electrical Issues
If any of the sensors are not working properly, the vehicle’s ECU/ECM may malfunction and respond with incorrect data, which can result in issues like slow acceleration.
Different types of vehicles use different types of sensors. These may include mass air flow sensors, MAP sensors, oxygen sensors, throttle position sensors, coolant temperature sensors, crankshaft sensors, camshaft sensors, and more.
The timing of combustion events and gas mixtures must be accurate for the vehicle to run efficiently and as expected, so inaccurate data about what’s going on in and around the vehicle can cause problems with acceleration and even starting the vehicle.
6) Airflow Issues (dirty air filters)
Air is a fundamental requirement for combustion, so restricted airflow will cause acceleration issues. This may be due to a clogged or dirty engine air filter. Manufacturers recommend replacing air filters regularly. Check your service manual and record when you replace them.
Please note that cabin air filters have a different function because they are part of the HVAC system and not the engine. However, if you search online you may find them simply called “air filters.” If you do replace your filter, be sure to buy the correct filter. The throttle body is a tube that contains the throttle valve (also called the throttle valve). If it sticks in a certain position or accumulates dirt, your vehicle will not perform as expected. If this is the case with your car, you may be experiencing rough idling.
7) Emergency Mode (Check Engine Light)
This failure may be due to a sensor failure, excessive engine knocking, or an issue with the emission control system. Limp mode typically causes the check engine light to come on and performance to decrease significantly.
8) Leaking or clogged vacuum hose
Engine vacuum is a measure of the air pressure in the intake manifold relative to atmospheric pressure. When the throttle is fully closed (idling, foot off the accelerator), the engine has the highest vacuum.
In this condition, the cylinders are trying to pull more air into the intake manifold than the throttle will allow, so the pressure in the intake manifold is significantly lower than the ambient air pressure.
When the throttle is fully open, the pressure in the intake manifold is nearly equal to the ambient air pressure. In this condition, there is little or no vacuum. In vehicles with a turbocharger (or supercharger), excess pressure can develop when the turbocharger or compressor forces compressed air into the manifold. This pressure is higher than the surrounding air pressure.
Vacuum hoses control the operation of many components around your vehicle, including the brake booster, fuel pressure regulator, and EGR valve. If any of these hoses develop a leak, it can cause the connected component to operate abnormally.
In a turbocharged vehicle, this can manifest as a boost pressure leak, causing the amount of air entering the combustion chamber to be significantly less than expected.
9) Low Compression
The ratio of the volume of the cylinder when the piston is at its lowest point to the volume when the piston is at its highest point is called the compression ratio. Compression is very important for the functioning and efficiency of an internal combustion engine because the higher the compression, the more powerful the explosion.
10) Great Heights
When driving at high altitudes, you may notice your car struggling or slowing down, especially going uphill. Oxygen is a key component of the mixture in the combustion chamber, and there is less oxygen at high altitudes.
In naturally aspirated cars, this problem is more prevalent than in forced induction cars (turbo or supercharged cars), because the engine can partially compensate for the lack of oxygen in the surroundings by blowing more air into the engine. Sensors detect that there is less oxygen and must draw in more air to compensate.
