A car will usually shake under acceleration if there is a problem with the fuel system (bad injectors, blocked fuel lines or fuel filter), if there are problems with the wheels (unbalanced or worn tires), if suspension parts are badly worn.
A problem with your car can often be more apparent when you push the engine a bit while accelerating. Under acceleration, vehicle components are often put under extreme stress, and this is when older or worn out parts can show their age or even fail.
It can also happen if the brake system is not operating properly (siezed calipers, worn rotors) or if there is a problem with the engine such as faulty sensors or a vacuum leak.
9 Reasons Why You car shakes when accelerating
1. Problem with the fuel system
When you push down hard on the accelerator, a surge of fuel is needed to power the engine. If there is a blockage or leak anywhere in the fuel system, then the engine will not be able to get the correct amount of fuel that it needs and this can lead to excessive engine shaking as it struggles to stay running.
Common problems with the fuel system include faulty fuel injectors, blocked fuel filters and faulty fuel pumps.
Fuel injectors operate under huge pressure and can fail mechanically over time due to the constant heat and pressure. They can also become blocked by dirt present in the fuel and carbon deposits from leftover residual fuel can build up on their tips. These problems will affect how efficiently the fuel injector works especially under acceleration when more fuel is needed by the engine.
A dirty fuel filter will restrict the amount of fuel getting into the engine. This can make it more difficult to start the engine and can also restrict acceleration. A common sign of a dirty fuel filter is lack of acceleration or power when need it.
Other fuel system problems can be caused by blocked fuel lines. Again, this will restrict the amount of fuel reaching the engine and will be more noticeable under acceleration. A faulty fuel pump that is failing mechanically or is partially blocked, will also starve the engine of fuel causing it to shake or possibly cut out under acceleration.
2. Worn Tires
The tires on your car are your only point of contact with the road. If the tires are not in good condition then you can expect a bumpy ride, and this will be especially noticeable when you are accelerating.
As a tire wears, the thread will decrease across the surface of the tire. This does not always happen in a uniform way, and this can cause a rough ride as the tire hits the road surface. A misaligned wheel will cause a tire to wear unevenly and this can cause the steering wheel to shake when going at certain speeds.
Usually a tire will wear more on one side than the other (ie more on the outside of the treads or more on the inside). This is fairly normal as most wheels do not stay 100% aligned for the life of the tire.
The shaking caused by an unevenly worn tire will be worse when the tire is near the end of its life as the softer tread rubber can absorb some of the uneven wear. When this is gone the tire surface can feel harder, and this can adversely affect the ride.
Another reason why a tire can cause shaking is if it is under inflated. An under inflated tire will have more contact with the road surface than it was designed to. This will affect how it wears and will also affect the handling of the car. You should always make sure that tire pressures are set to the correct level and check them weekly.
3. Badly Worn rotors/brake pads
Another common cause of shaking when accelerating is worn or warped brake pads. Brake rotors are precision engineered parts that need to sit perfectly flat on the wheel hub and must have an extremely flat surface for the brake pads to squeeze against.
Over time, brake rotors will wear and small ridges and other imperfections will appear on the surface of the rotor. These will cause the brake pad to wear unevenly as it the pad is softer and will take the shape of the surface of the rotor. If the surface of the brake pad is not smooth, then the pad will vibrate as the rotor turns against it. This can cause a vibration behind the wheel that you can feel in the steering wheel, suspension or brake pedal.
It’s important to check the condition of brake components regularly to ensure that the rotors, pads and callipers are all in good condition and performing smoothly as they should.
4. Seized Brake Caliper
Just like the brake rotors and brake pads, the brake calipers can also become worn and can actually start to stick.
In a hydraulic brake system, when the brake pedal is pressed, a pushrod exerts force on the piston(s) in the master cylinder, causing fluid from the brake fluid reservoir to flow into a pressure chamber through a compensating port.
The brake calipers on your car are responsible for squeezing the brake pads against the rotor when you push down the brake pedal. Calipers are operated by the brake fluid pushing against a piston that intern pushes against the brake pad.
Sometimes the rubber seals around the pistons can become torn or just wear from being exposed to heat and high pressures. This can cause the piston to seize in the caliper. If the piston doesn’t move smoothly, then it can cause the brakes to stay on after you have take your foot off the brake pedal.
A seized brake can cause a vibration that will get worse as you accelerate. Signs of a seized brake caliper include a vibration in the wheel, a vehicle that pulls to the left or right as you brake and a burning smell coming from the brake caliper.
5. Unbalanced Wheel
When you get a new tire or wheel fitted to your vehicle, it’s necessary to get the wheel balanced. In order to balance the wheel, one or more small weights are fitted to the inner rim of the wheel.
The weight that is fitted to a wheel is actually a counterbalance that is canceling out an imperfection in the shape of the wheel. Even if a wheel and tire are both brand new, they will still need balancing.
If a wheel is not balanced properly, or a weight falls off then the wheel will vibrate as it turns because it weighs slightly more on one side. This vibration will increase as you accelerate and can often be felt as a shake in the steering wheel at higher speeds.
If a wheel is left unbalanced it can cause premature ageing of the suspension and tires and can affect the handling of the car especially when braking or turning.
6. Worn Suspension Parts
Worn out suspension parts and rubber suspension bushings are a very common cause of a car that vibrates when accelerating.
Most suspension parts consist of a metal part and a rubber bushing that dampens vibrations at the point where the suspension part is bolted to the subframe or wheel assembly. As the rubber bushing ages, it begins to lose its shape and can shrink and harden. As a result, the suspension part will become slightly looser and may start to move around and vibrate as you drive.
This vibration is usually felt directly in the steering wheel, the pedals and in the wheels. It will usually get worse the faster you go, as the vibrations will increase with speed.
Worn out suspension parts can really affect the handling of your vehicle and should always be replaced before they get too worn. Common problem areas that will usually wear out first include sway bar bushings, drop link bushings and shock absorber bushings and upper mounts.
7. Faulty Engine Sensors
All modern engines rely on sensors that keep track of all areas of the engine. These sensors then relay that information to the vehicles ECU, usually in real-time, so that the ECU can make adjustments to the fuel and air supply components to keep the engine running smoothly.
If a sensor is failing, is dirty or is broken, then it won’t be able to work properly, and will give a bad or out of range reading to the ECU. This can wreak havoc with how the engine runs, leading to a loss of power, especially during acceleration. A badly running engine can vibrate and stutter and even cut out.
The most problematic engine sensors that can cause an engine to run badly are the mass air flow sensor (MAF sensor) and the manifold absolute pressure sensor (MAP sensor)
Problems with these sensors will cause your engine to run rough, causing excessive vibrations ad shaking when accelerating. Early symptoms of a failing MAP sensor include engine misfires, decreased fuel efficiency, rough engine idle and decreased power especially when accelerating.
8. Dirty Fuel Filter
A dirty fuel filter is an often overlooked cause of why a car will shake when accelerating, especially when weighed down or going uphill.
The fuel filter is there to filter out impurities in the petrol or diesel used to run your car. If left unchecked, it can become clogged up with debris from the fuel. A blockage in the fuel filter is going to affect the amount of fuel available to the fuel pump and the fuel injectors.
Sometimes a partially blocked fuel filter will not show any symptoms until you go to accelerate. It’s at this point that the fuel gets blocked, the fuel pressure drops and the engines ECU will detect a problem. The reason the car shakes is because the fuel to air ratio is knocked out by the sudden lack of fuel, causing the engine to misfire and stutter.
To avoid any potential problems with a fuel filter, you should change it every 30,000 miles or sooner.
9. Problem With the spark plugs
Bad spark plugs are also a very common reason why your car shakes when accelerating. Spark plugs can fail in a number of ways and for a number of reasons.
An example of a dirty, worn out spark plug
The most common reasons are a carbon build up on the tips of the spark plugs, corroded or burned spark plugs and oil on the spark plugs.
The Cost Of Repairing A Car That Shakes When Accelerating
It can cost anywhere from $10 (the cost of getting a tire balanced) to a few hundred dollars if the fix involves new suspension or brake parts.
It can be difficult to put a price on fixing a car that shakes when accelerating because there are many different causes. Here are a few sample repair costs, assuming you are carrying out the work yourself. If you are paying a mechanic to perform the repair you can expect to pay more.
- Replacement Fuel Filter: $10-$30
- New Spark Plugs: $40-$80.
- Wheel/Tire Balancing: Approximately $10 to get a wheel professionally balanced. Sometimes the problem is caused by a buckled wheel or a damaged tire. A replacement wheel or tire can cost hundreds of dollars depending on your vehicle.
- Replacement brake parts: $100+ dollars. If there is a problem with the rotors or calipers then it’s a good idea to change the brake pads also.
- Fuel system problems: Modern vehicles have more complicated fuel systems and can be difficult to troubleshoot. They are also more expensive to fix if the problem is not just a dirty fuel filter. Replacement fuel injectors can cost from $200 to replace with fuel pumps costing $400-$500 on some vehicles.