Hey, Why Is My Car Not Accelerating?

If you are short on time and want to fast-track the process to professional help, click Yes

Four common causes for the vehicle accelerating badly and their related parts.
The modern vehicle is operated by what is called fly-by-wire. The computer controls the vehicle based on the inputs from the driver through wires and then commands the car to do what it is supposed to do through cables. When there is input such as the gas pedal, the computer then tells the engine at what rate and how fast to accelerate based on how the driver operates the gas pedal. As long as there is adequate fuel and air, the engine will typically provide enough power to accelerate. The vehicle will not respond accordingly if any input and output sensors are not reading correctly.

Is Your Car Unable to Accelerate?

Your car isn’t accelerating because it has a low fuel flow. A clogged air filter, faulty injectors, or a damaged fuel pump might be the culprits. Alternatively, it can be damage to spark plugs or the timing belt.

If you're noticing a slow acceleration or a complete difficulty in accelerating your car, take note of the issue. Car acceleration problems can be a safety hazard to you and other drivers.

There are several reasons why your car won't accelerate properly, ranging from simple issues like low fuel levels to complex problems like a faulty transmission or fuel pump. Unfortunately, troubleshooting and fixing the issue alone can be risky if you lack the necessary expertise or equipment.

For this reason, it's advisable to seek assistance from a professional mechanic promptly. They possess the knowledge and tools required to identify the root cause of the problem and make necessary repairs. Not only will this guarantee that your car runs smoothly and efficiently, but it can also prevent poor acceleration issues.

Let's Get To The Bottom Of It!

  • Q: Is the car cranking for a long time before starting?

    The fuel filter is like a strainer for your car's gas. It catches any dirt or junk in the gas or from the fuel pump, preventing it from entering the fuel injectors and clogging them. But, if the fuel filter gets too dirty from wearing out, it can slow the gas flow to the injectors. This can make it harder for the car to start up quickly.

  • Q: Is the vehicle most struggling to accelerate after being driven for a while?

    The catalytic converter is like a cleaner for the dirty air from your car's engine. It needs a mix of fuel and air to work properly and stay clean. But, if your vehicle has a problem, like using too much or too little gas, or if oil or coolant is getting into the exhaust, the catalytic converter can get damaged and start to get blocked. When this happens, pressure builds up in the engine, making it harder for the car to speed up. You might notice this more the longer you've been driving the vehicle.

  • Q: Is the "check engine" light on the dashboard?

    The timing belt is like a conductor that helps the engine's parts work together in perfect harmony. It ensures that the crankshaft and the camshaft are in sync so that the valves open and close at the right time. But, if something goes wrong and the timing belt slips or is installed incorrectly, the engine's sensors will notice and turn on the check engine light to let you know something is wrong.

  • Q: Has the vehicle's fuel economy dropped?

    Spark plugs are essential components of the engine that help produce energy to move your car. They are like small screws tightly screwed into the engine's cylinders. When the engine turns on, the spark plugs help create a spark that ignites the fuel in the cylinders, generating power to move your car. Over time, the seals that keep the gases inside the cylinders can start to fail, and this can cause problems. When the seals are not working correctly, the gases escape, and the engine's efficiency will decrease. This decrease in efficiency can cause your car to use more fuel than it should, which means you'll have to pay more for gas.

Find Professional Help

Please select your vehicle's brand and location so we can locate the best professional help for you
If you are a shop owner and sick of business directories that are based on the cost of repair, AutoTechIQ is for you. If your customers receive Digital Inspection results then AutoTechIQ is definitely for you. Check out the certification page or how to rank in your area.

Vehicle Health Inspection Proof

Explore the following typical inspection results that show a potential cause for the symptom and select the one you believe is similar to your vehicle's issue.

Faulty fuel pump

The technician showed the customer proof of the diagnosis by providing an image of the fuel pressure tester checking fuel volume by measuring how much fuel was pumped in a specified time.

A brought in their car and explained to the technician that while driving down the freeway, the vehicle started to stumble and wouldn't accelerate as fast as needed.

During the technician's test drive, they confirmed that the vehicle was stumbling on hard acceleration. The technician did a vehicle health inspection for potential issues but found nothing related to the customer's concern. They did notice, however, that the car did not have an inline fuel filter.

With the customer's approval for additional diagnostics, the technician used a vehicle-specific scanner to check for any current or pending trouble codes. Again, they found no codes present.

To investigate further, the technician hooked up a mechanical gauge to the fuel system and found that the fuel pressures were at the manufacturer's specifications. The technician then performed a flow test on the fuel pump by energizing it with the scanner and catching the fuel in a metered cup to compare it with manufacturer specifications.

Finally, after comparing the amount of gas pumped in the allotted time, the technician found that the flow was well below manufacturer specifications.

Does the issue look like this? if not accessible your shop will document it
Clogged fuel filter

The proof image showed where the pressure on the fuel filter could be tested to confirm that the filter was restricted.

A customer dropped off their vehicle and reported it was cranking for a long time before starting. This meant that if they left the car unused for 15 to half an hour, the engine would take about a minute of cranking before it started. However, if they tried to restart the vehicle immediately after turning it off, the engine would start right up.

During the test drive, the technician confirmed that the engine took a while to start. However, the technician didn't notice anything unusual during the vehicle health inspection. Therefore, the customer authorized additional diagnostic costs to get to the root of the problem.

The technician used a specialized scanner to check for trouble codes but found none. They then checked the fuel pressure at the fuel rail, finding that it took extra time to build up to the manufacturer's specified pressure. The technician also noticed an inline fuel filter that didn't look like it had ever been replaced.

Next, the technician hooked up a pressure gauge to the pressure side of the filter and found that the pressure immediately came to the manufacturer's specifications. However, the pressure on the outlet side of the filter took a while to build up, indicating that the fuel filter had a restriction.

This restriction was causing the long cranks the customer reported. The technician determined that the fuel filter would need to be replaced to solve the issue.

Does the issue look like this? if not accessible your shop will document it
Faulty spark plug seal

The technician's proof image shows evidence of the combustion gas leaking by the spark plug seals, which helps to explain why the customer's fuel economy has been decreasing.

When the customer dropped off their vehicle, they mentioned their fuel economy gradually decreased, and they wondered if they needed a tune-up.

The technician did not notice anything unusual during the vehicle health inspection or the test drive; the car was acting normally.

However, the customer authorized additional diagnostics, and the technician used a specialized scanner to check for trouble codes. No trouble codes were present, but the technician suspected the spark plugs might be onto something.

They accessed the spark plugs for inspection and found wear signs. But, even more concerning, the seals between the metal and porcelain were blown, and combustion gas leaked.

The spark plugs need to be replaced to solve this issue. The spark plugs are an essential part of the engine that ignites the fuel, allowing the engine to run. If the spark plugs are worn out, they will not perform as well, causing fuel economy to decrease.

Furthermore, when the seals between the metal and porcelain are blown, combustion gas can leak out, resulting in poor fuel economy, as observed in this case.

Does the issue look like this? if not accessible your shop will document it
Loose timing belt causes whining noises, also triggering the check engine light and making the car not accelerate

The technician provided a proof image showing that the intake cam had jumped a tooth on the timing belt. This misalignment was causing the check engine light to come on and the vehicle to lack power.

When the customer dropped off the vehicle, they reported having the timing belt replaced by an amateur, and now the check engine light was on, and the car was lacking in power.

The technician who test-drove the car confirmed that the check engine light was on and that the car wasn't accelerating as it should be. However, the technician noticed no problems during the vehicle health inspection.

To investigate further, the technician conducted a vehicle code scan which revealed a p0341 code, indicating an issue with the camshaft position sensor circuit.

The technician used a dedicated scanner to check the code and visually inspected the cam sensor and wires but couldn't find anything wrong. To get a better look, the technician removed the timing belt cover to ensure the timing was set correctly.

It turned out that the intake cam gear was off by one tooth, which can cause the engine to run poorly and the check engine light to come on. In addition, the water pump, tensioner, and pulley appeared worn out, so the technician recommended replacing them and resetting the cam timing.

Does the issue look like this? if not accessible your shop will document it
Clogged catalytic converter

The proof image showed the technician checking the back pressure with a gauge, which proved that the catalytic converter was clogged. This results in issues to control exhaust gases.

A customer brought their vehicle to the repair shop and said they were experiencing a power loss while driving. They suspected the car was running out of gas.

During a test drive, the technician noticed that the car had no acceleration at full throttle and that the check engine light was on the dashboard. The technician did a vehicle health inspection to diagnose the problem but found nothing related to the customer's concern.

They also scanned the car's computer and found a code for P0420, meaning the catalytic converter was not working correctly. The customer authorized additional diagnostics, and the technician used a thermal imaging scanner to check the temperature before and after the catalytic converter.

They found that the temperature before the converter was 100° hotter than the outlet temperature, which indicated that the converter was not working. They removed the primary O2 sensor and installed a back pressure gauge to confirm this.

Next, they started the vehicle and watched the gauge, which showed that the back pressure was out of normal range, confirming that the catalytic converter was restricted and needed to be replaced.

However, the technician also noted that further diagnostics would be needed to determine why the catalytic converter failed. This would involve investigating the ignition and fueling systems.

Does the issue look like this? if not accessible your shop will document it
Faulty injector

The proof image shows that the injector drivers coming from the ECM had failed. The technician took a picture of the Noid light plugged into the injector harness; the light should activate, but it didn't. This results in an improper air fuel ratio during combustion.

The customer noticed that their vehicle had a rough idle and that the tachometer needle was jumping around. The issue did not affect the car under normal driving conditions, but the check engine light was on and would occasionally flash.

The technician took the car for a test drive and noticed the rough idle. During a vehicle health inspection, the technician found nothing related to the customer's concern. They performed a vehicle code scan and found a P0302 code for a detected misfire on cylinder number two.

After receiving authorization for additional diagnostics, the technician used a scanner to verify the number two misfire and watch live misfires. They discovered the number two cylinder had a dead miss, and the spark plug was fuel soaked.

The technician checked the spark plugs in numbers four and six, which appeared okay. Then, they performed a compression test on cylinders 2, 4, and 6, finding they were within 10% of each other. This indicates that the engine's cylinders produce relatively equal amounts of power and operate as they should.

The technician then moved the number two spark plug to the number four location and switched the number six coil with number two. They cleared the trouble codes, started the vehicle, and still got the issue.

The technician disconnected the electrical connector going to the number two injector and installed a Noid light. Then, they started the vehicle, and the Noid light didn't activate, indicating a lack of signal to the injector. After checking the wirings and other related probable causes, the technician concluded that a lack of drivers caused the issue. So, they would need to replace the injector.

Does the issue look like this? if not accessible your shop will document it

Typical Fixes to Address the Cause(s)

The following chapters bases themselves on experiences from our auto repair shop; we'll describe related problems' causes and fixes.

"Engine control module replacement" fixes "Faulty injector"

The AutoTechIQ ranking for Safety, Cost Avoidance, and Environmental Impact is

env level
env level
Cost Avoidancei
env level
env level
Environmental Impacti
env level
env level
Hey, Why Is My Car Not Accelerating?
Sometimes a problem is more challenging to describe than it initially looked like. If you are not sure your problem is described by this article, please find below similar vehicle symptoms, which might describe better the issue you are experiencing.

Other things your auto repair shop might talk about:

Engine speed. Gas pedal. Combustion chamber. Combustion process. Clogged air filter. Mass air flow sensor. Accelerating properly. Fuel mixture. Gas tank. throttle body. oxygen sensor.