Car hesitates when accelerating diagnosis

Every modern car apart from electric cars has an air, fuel and spark system. These system work together to improve fuel economy whiles mitigating emission. When any of the system mentioned above is not operating as it should, one of the problem that surface is the car hesitating when accelerating. What this means is, loss of power or stalling when you press the gas pedal, it it delays in response, causing the car to jerk or lurch forward. Apart from this three system there are other associate components like the oxygen sensor, throttle body and sensors and mass airflow sensor that can also trigger hesitations when accelerating.

Technically, car hesitating when accelerating is known to be a lean mixture situation, creating less power. Let dive deeper into how to diagnose a car hesitating when accelerating into details.

Plot PID’s if possible - Plotting the basic PID’s using an auto scan-tool is the first step to evaluate the main cause of the car hesitating when accelerating. Typically the 02 sensor, TPS sensor, MAF sensor, fuel pressure sensor, and finally short/long term fuel trim values. You can also evaluate the misfire from freeze frame data if not cleared to check whether the problem also stems from there. Let takes this sensors one by one in addressing car hesitating when accelerating. 

The 02 Sensor: This sensor like the spark plugs tell a lot about the performance of the vehicles, especially why the car hesitates when accelerating. If an 02 sensor is stuck at less than 0.3mV, its an indication that the reading is a false reading if the oxygen sensor is not faulty. False readings like a lean value is triggered by vacuum leaks, low fuel pressure or spark coil, wires and plugs not functioning well. If spark is performing otherwise, there is a certainty that misfire will be the order of the day. Why because constant dampening of fuel into the chamber due to a lean condition will foul the spark-plugs, prevent complete burnout and then misfire. Misfire should be the last step of your diagnosis because bad 02, vacuum leaks, low fuel pressure can cause misfire, tackle those first. Wen tackling misfire, you are considering looking into ignition related components like plugs, coils, wires, circuit, crank and cam. So you can see that, the car hesitating when accelerating stems from a broader issue, but narrowed to air, fuel and spark system.. Now that the 02 sensor has given you a better picture, lets look at some of the PID’s listed above to pin-point the problem 

Air System- A dirty air filter can restrict air airflow and cause engine to run lean. A faulty or dirty Mass air flow sensor can also cause a car hesitate when accelerating why? Because it measure the volume of air going into the engine combustion chamber through the manifold and signals the PCM to calculate injector pulse and ignition timing. If this air is not measured, fuel pulsed will fall short of the air/fuel ratio, leaning the mixture because there is more oxygen, causing the car to hesitate when accelerating. If readings from you scan-tool is normal 8-10hz at idle and 40-45hz at wide open throttle you MAF is perfect. Only jump to Short and Long term fuel trim values to find out if MAF readings is over the bar..

Fuel trim values - Yes you know by now that you have a lean problem because of the 02 sensor sensor, but don’t know whether its a vacuum leak. The fuel trim values will always direct you as such, an important PID for diagnosing car hesitating when accelerating. Fuel trims in combination with throttle body and sensor helps you narrow down the problem. If the cars throttle sensors or body is bad, your results will skim. Ensure your TPS is working as it should before continuing with car hesitates when accelerating diagnosis. If the lean condition is caused by a vacuum leak, you will see high fuel trim values during idle but normal values during high rpm. Run the engine from idle to high rpm 3500 to find out. If fuel trim values are normal during idle but high during high rpm replace your MAF or fuel pump because the pressure is low. So you find out from the short and long term fuel trim values with varying rpm to diagnose car hesitating when accelerating because of a lean condition. How then do you conclude its not MAF but lower fuel pressure issue that makes the car hesitate when accelerating?

Click here to read more about using fuel trim values for diagnosis.

Fuel System - If MAF readings are good, but you’re reading high fuel trim values during high rpm go for the fuel system. Its either the car is experiencing flow problem, or pressure problem. Normally a high fuel pressure will indicate ok or low fuel trim values at both idle and high rpm so take note of that. Again your scan tool is your best friend if you don’t have fuel pressure gauges. Also, quickly check the fuel tank for fuel before troubleshoot fuel quality, fuel pump motor, clogged fuel filter preventing fuel from reaching the injector housing as well as fuel line for leaks and wear that decreases the pressure and volume of the fuel. If all the above comes to play the car won’t start at all.

Click here to read more about troubleshooting Car won’t start

Finally Misfire - emerging for the ignition system, no matter how much fuel is present, without a spark, there won’t be any explosion to create the downward force of the piston, which is needed to turn the crankshaft as in start issues. Also without quality spark there would be misfires. But in this car hesitating when accelerating case, there is spark, just that it’s not adequate or performing as its should due the constant dampening of the fuel commanded by the PCM. This is another broad topic on its own since a lot ignition siblings is involve. Follow this link to read more about ignition diagnosis

Final thought - now you know that the air, fuel and spark system can contribute to car hesitates when accelerating. Deciphering which system is the culprit warrants a professional scan-tool and deep understanding about how these three systems works.

Visit Adei-yie shop for further diagnosis, if you can’t fix the above issues yourself.  

Having lots of 5-star rating reviews don’t hesitate to visit the Adei-yie shop for further diagnosis, if you can’t fix the above issues yourself.  Adei-yie does not only help you figure it out or fix your car quickly but also stands behind all estimates guaranteeing fair pricing & 4,000-mile warranty for all replacement parts.

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