It can be frustrating for any driver to expect certain acceleration from their car only to find that the car seems to be hesitant while speeding up. This hesitation could be potentially dangerous in situations like entering and exiting the highway from an off-ramp, where acceleration may be required to merge with traffic. A vehicle that struggles or hesitates to accelerate may be unpredictable and moments of hesitation may be coupled with equally dangerous moments of surging or unwanted acceleration. When a car is hesitating during acceleration, it should be checked by a mechanic.
How this system works:
A car with a combustion (gas or diesel) engine needs an exact mixture of fuel and air to run efficiently. If this mixture is thrown off in any way, it may result in an engine running too lean (not enough air), or too rich (not enough fuel). An engine that is hesitating to accelerate is most likely dealing with a fuel/air mixture that is too lean. Engine’s that are running inefficiently will start to show signs like hesitation which will only become worse over time. If you notice some signs like hesitation, you should have your car inspected immediately.
Common reasons why this happen:
- Mass Airflow Sensor:The mass airflow sensor measures how much air is going through the engine and relays this information to the car’s computer so that the right amount of fuel can be delivered from the fuel injectors. When a mass airflow sensor starts to fail, it will typically generate an error code or “Check Engine light.” This warning may be followed by hesitation while accelerating, or while driving up a hill. A car with a failing mass airflow sensor may also stall soon after starting.
- Fuel Pump:The fuel pump in most modern cars sits inside the fuel tank and pumps fuel up to the engine. If a fuel pump cannot offer the correct pressure, fuel may have difficulty making it to the engine. A car that hesitates while accelerating or while driving up a hill may have a weak fuel pump.
- Throttle position sensor:A throttle position sensor signals the vehicle’s computer how far the throttle is open and how hard the accelerator is being pressed. The computer is then able to adjust the fuel/air mixture going to the engine so that is stays at an appropriate level. If the throttle position sensor is not functioning properly, it may be sending incorrect information to the vehicle’s computer. The computer may then not give the engine with the correct amount of air while accelerating, causing a hesitation sensation.
- Dirty/failing fuel injectors:Fuel injectors spray fuel in a fine mist into the cylinder where it is then mixed with air and ignited by a spark plug. Fuel injectors may get dirty over time and not be able to provide as much fuel to the cylinder as is needed. Dirty fuel injectors may cause the engine to run lean which will in turn, cause hesitation when accelerating.
How it’s done:
A mechanic will first plug into your car’s computer using a code reader/scanner to better identify what the exact issue is. In addition to reading trouble codes, he or she should also be able to get readings of oxygen/fuel intake to make sure those numbers are where they should be. Once the mechanic gets this signal they can begin to fix any potential issues.
If the mechanic thinks that the mass airflow sensor has gone bad or is failing, he or she will first check the sensor for any superficial damage. The mechanic will also ensure that the sensor is wired correctly and that no damage has been done to the wire harness. The mechanic should then take out the mass airflow sensor and replace it with a new one if necessary.
If the mechanic feels the problem is the fuel pump, he or she will remove the fuel tank if necessary to inspect the pump. If the pump has indeed failed, the mechanic will change it. If the fuel tank itself it beginning to show signs of age, it may be convenient to change the pump and tank at the same time.
If the mechanic thinks the throttle position sensor, he or she will test the throttle position sensor and it’s wiring to see if it is functioning normally. If it is not, the mechanic will remove the throttle positioning sensor and the wiring and change them. In between removing the old sensor and replacing the new one, the mechanic should take the opportunity to clean the throttle body. The mechanic will then ensure the new throttle positioning sensor is working properly and transmitting the correct information to the car’s computer.
If the mechanic feels the problem is dirty or failing fuel injectors, he or she will check the injectors to check for any signs of damage or leakage. The mechanic should also take this opportunity to change the fuel filter if it is not a part of the fuel pump. They will then replace the injectors and test them to make sure they are functioning properly.
In all situations, the mechanic will start the car to make sure that all of the new components are working properly. In the event that an issue has caused a warning light to come on, the mechanic will be able to clear the trouble code associated with the light using a reader/scanner.
How important is this service?
Sluggish acceleration can be irritating for drivers who expect more power form their car, but it can also be dangerous in certain situations. The unpredictable nature of an engine that hesitates can increase the chance of a potential accident especially when trying to merge in and out of heavy traffic. If you notice that your car seems to be underpowered, especially when accelerating, you should not drive it if possible until it can be checked by a mechanic.