There’s nothing as scary and frustrating as a car doing what you don’t expect it to. Your vehicle should slow down when you hit the brakes and accelerate when you step on the gas pedal.
Imagine how scared you will be when merging or overtaking and hitting the gas pedal only to get nothing. The vehicle doesn’t rev up and accelerate or revs up but doesn’t seem to pick up speed.
Such a scenario means there’s a problem somewhere in your drivetrain. Dealing with it as soon as possible restores confidence in your vehicle, making it safer to drive on the freeway.
How Do Cars Accelerate?
When you push on the accelerator pedal, several things happen within the engine and the transmission to make your vehicle pick up speed.
The Engine Revs Up
Stepping on the accelerator forces your engine to rev up. Higher revolutions bring the engine closer to its peak torque and horsepower output band. Additionally, more revs translate to faster spinning wheels.
- The gasoline engine’s accelerator pedal opens up the throttle body, letting more air into the system. This forces the engine the injectors to dispense more fuel and the engine to run faster
- Diesel engines accelerate by altering how much fuel they inject into the cylinders. Air intake is dependent on how much fuel gets into the engine.
Anything that affects your engine’s combustion and performance will affect what happens when you put the pedal to the metal. Also, a problem with the accelerator pedal and system will impact what happens when you press the accelerator pedal.
Your Transmission Selects the Perfect Gear
As the engine revs up, your gearbox must match this by selecting the right gear to put as much torque to the wheels as possible.
An automatic transmission will downshift to the right gear on its own. If it delays downshifting or doesn’t downshift, the engine will be ‘overloaded’ and won’t rev up as much. This means you won’t get more power to start with. Additionally, since the gears are so high, you won’t put as much torque to the ground hence slow acceleration.
In a manual transmission, it’s up to you to downshift on demand to ensure you get as much acceleration as necessary when you hit the gas pedal.
Why Isn’t You Car Gaining Speed When You Hit the Accelerator Pedal?
With this in mind, we can look at some of the things that will prevent your car from accelerating well every time you hit the accelerator pedal hard.
Power Restricted or Valet Mode is On
Some very powerful vehicles with high horsepower and torque outputs have a valet mode or restricted power mode that lets you limit how fast or how hard the car accelerates.
The mode is designed to stop other operators from pushing the vehicles harder than you want because you don’t trust them. This could be used when you give your vehicle to your kids, a friend, or the valet.
If your vehicle has such a feature, confirm that it’s not on once you notice a dip in performance. You should have a password to enable and disable the limit if it’s your vehicle.
You Have a Speed Governor
Many companies or commercial vehicles have a speed governor. This ensures the vehicle doesn’t exceed a predetermined speed. If yours has one and you try to accelerate when you’ve hit the speed limit, then you will get no increase in speed.
You Are Driving in High altitude Area
Air gets thinner the higher you go. That’s why mountaineers have to pack oxygen when going up very high mountains. Since your internal combustion engine needs oxygen to produce energy, its performance will suffer when driving high mountain passes.
The reduced oxygen per volume of air could see you lose up to 20 percent of your engine’s performance when going to high altitudes. Luckily, this isn’t a problem, and your engine’s performance will get back to normal once you come down to denser air.
There’s Something Under the Brake Pedal
Another simple problem that could hamper your acceleration is something stuck under the accelerator pedal. This will make you think you have the pedal to the metal while, in reality, you’ve only accelerated less than halfway.
Keep your car clean. Junk, water bottles, and other containers stuck under one of your pedals is dangerous. It could stop you from fully accelerating or braking perfectly.
Your Parking Brake is Engaged
Driving with the parking brake on impairs your vehicle’s performance. The resistance, though small, will affect how powerful your car feels when you accelerate.
Luckily, most modern vehicles will beep at you and display a warning light if you keep driving with your parking brake partially engaged. Those with an E brake won’t even let this happen in the first place.
If you have the manual emergency brake, ensure it is fully released before driving. This will give you excellent acceleration, good fuel economy, and a longer lifespan on your rear brake pads and rotors.
You Have Fuel Delivery Problems
Your engine’s performance depends on fuel efficiently getting to the combustion chambers per cycle. Anything that affects fuel delivery will have a direct impact on acceleration. some of the most common fuel system issues include:
- A weak or damaged fuel pump
- Clogged or damaged fuel injectors
- Clogged fuel lines
- Dirty or clogged fuel filters
- A faulty high pressure fuel pump
- A leak leading to low fuel pressure
Sometimes each of the above problems will trigger an error code or adrift in live data that a good OBDII scan tool will detect.
At other times, all it takes is some good old troubleshooting and looking for tale-tale leaks or silence when you expect a fuel pump hum.
Issues With Your Air Delivery System
Air is just as important as fuel. Anything that chokes your vehicle, preventing how much high-quality air gets to the combustion chamber, will have a profound impact on how much power you generate.
In naturally aspirated engines, problems range from:
A dirty or clogged air filter
Clogged air filters limit airflow. The engine sucks less air and gets less oxygen during the combustion cycle. This translates to less power. You should never encounter this problem if you change your air filters every time you service your vehicle.
However, your air filter will block up if you frequent country roads with a lot of dust and bugs or drive in traffic jams with a lot of smog. Keep inspecting your air filter now and then and dust it off between service stops to keep your engine breathing optimally.
A damaged cold air intake
A cold air intake ensures that your engine ingests cold denser air instead of all that hot air milling around under the hood. While they used to be the staple of aftermarket modding, most modern cars install stock cold air intakes to improve fuel economy and emissions.
If your cold air intake is cracked or missing, your car will lose a fraction of its punch. It might not be that much, but you’ll notice it when accelerating hard on a loaded vehicle.
A vacuum leak
Another problem that could rob your engine’s performance is a vacuum leak. Vacuum leaks throw off fuel trims hence the potency of each combustion cycle. Finding and fixing vacuum leaks will save your engine and improve fuel efficiency.
More things could affect power delivery and engine performance if you have a forced induction engine with a turbocharger or a supercharger. These include:
A faulty turbo or supercharger
If your turbos or supercharger fail, you’ll notice. Forced induction engines rely heavily on boost to produce that extra horsepower and torque. You will lose a considerable amount of power when it goes missing.
Luckily, your boost gauge or readout will quickly let you know when you have less than normal or no boost at all.
Turbo lag
Know the famous turbo lag? A turbo needs fast-flowing exhaust gases to produce maximum boost. That’s why there is a slight delay between putting the pedal down and the real power kicking in in most vehicles.
If you are used to the vehicle and are not expecting split-second performance, you might not notice the lag at all – or you will anticipate and plan for it.
ProTip: Aftermarket turbos tend to be laggier since very few people perfectly tailor their airflow capabilities to the exhaust.
A faulty intercooler
The final problem in a supercharged or turbocharged engine could be the intercooler. Since engines prefer cold air and turbochargers heat up the intake air, engineers push the air through a cooler before feeding it to the engine.
A faulty intercooler that is either clogged or inefficient at cooling won’t work efficiently and will starve your engine or feed it hot oxygen sparse air.
A Faulty Mass Airflow Sensor
Fuel-injected engines use the mass airflow sensor to determine how much air gets into the engine. This is very crucial as it determines the air/fuel mix that ends up in your cylinders.
A bad sensor will throw off the ideal mix making your engine lethargic or more fuel-hungry. We did a post on mass airflow sensors. You can check it out to learn more about their impact on your engine.
Your Engine Is Misfiring
A misfiring engine is never efficient. It isn’t firing all the cylinders and is letting fuel go to waste without transforming it into torque and horsepower. As such, it will be weaker than an engine firing on all cylinders.
Common things that could cause misfiring include:
- Bad or fouled sparkplugs
- Damaged ignition coils
- Wrong injection timing
- The wrong fuel/air mixture
- An electrical problem
- Poor compression
- Compromised fuel
Issues With Emission Control Sensors
With governments getting stricter with emissions, manufacturers have no option but to install intelligent emission monitoring and control systems.
In most vehicles, these systems adjust fuel use to ensure your truck efficiently burns fuel, producing byproducts the PDF and catalytic converter can deal with.
Faulty sensors on this system could give the wrong feedback forcing your engine to compensate in a way that reduces engine output.
A Faulty Throttle Position Sensor
Drive-by wire vehicles use a throttle position sensor to tell the ECU how hard you want to accelerate. It translates the gas pedal position into a value the ECU can understand.
If this sensor is faulty, it could lag behind your instructions with the gas pedal or understate how hard you push on the pedal. This will lead to a no-accelerate feel on your vehicle each time you push the gas pedal down.
A Clogged Exhaust System
A clogged exhaust system creates more than necessary backpressure that, in turn, reduces how much power the engine sends to the wheel.
A clog could be something as simple as a malicious block on the tailpipe or something as serious as a clogged PDF or catalytic converter.
A Problem With the Transmission
Besides the engine limiting your acceleration, the transmission could also be the problem. If it keeps to a higher gear, you won’t put as much torque to the ground as necessary to accelerate fast.
When this happens, perhaps:
- Your transmission shifts slowly because you are low on transmission fluid
- Your car is in Eco mode and holds high gears longer or shifts up faster
- You are driving a CVT and are not used to how they behave
- You are on manual mode and are not shifting down on time
You Are Not Shifting at the Right Time in a Manual
If you drive a manual, you should by now know how important it is to be on the right gear for acceleration when passing. If you just put the pedal to the metal without downshifting, you will not get as much acceleration as you wanted.
Luckily, this is a user problem, and your vehicle is perfectly normal—nothing to worry about.
A Slipping Clutch
Manual vehicles use the clutch to transmit power from the engine to the gearbox. A clutch should form a perfect mesh when fully engaged.
A worn out clutch will slip, losing some of that sweet power as friction. Slippage will also happen if you ride the clutch as you drive along.
Your Vehicle is in Limp Mode
Another technical problem limiting how hard your vehicle accelerates is limp mode.
The ECU and powertrain control module will put your vehicle in limp mode if it detects a fault that could cause further damage should you keep driving normally.
An overheating engine, transmission, a misfire, low transmission, and oil levels are among the things that could put your vehicle in limp mode.
Luckily, an error code will pop up with the check engine light, and an OBDII scanner will tell you why your vehicle went into limp mode.