Engine Hesitation
Check for Broken or Dilapidated Vacuum Hoses - Inspection of
the vacuum hoses or air intake boot on and around the engine is simple. Your car's
engine is designed to run on a system that can hold vacuum. Vacuum hose are typically
connected to the engine intake manifold and will supply engine vacuum to various
accessories like power brakes. Some cars are designed with a larger vacuum transfer
hose that connects the intake manifold to the
IAC (idle air control) motor.
If broken or dilapidated these vacuum lines can cause the engine to lose vacuum
which will allow the engine to
run rough and stall.
Inspect all engine and accessory vacuum lines look for missing, torn or dilapidated
lines and replace as needed. Also have a helper rest their foot on the gas pedal
just enough to keep the engine running and double check the engine when it is running
to listen for any whistling noise coming from the engine that is not usually present.
Follow the noise and inspect vacuum lines in that area, also when the engine is
running it will pull inward a broken or weak piece of the hose to create a larger
vacuum leak. Check the integrity of all vacuum hoses at each end of the hose, typically
this is where a vacuum hose fails. If all vacuum hoses check "okay" proceed to the
next step.
Failed Air Intake Boot
Replace Air Intake Video
Check Fuel Pump Pressure and Pressure Regulator - Fuel pump is worn providing low fuel pressure to the fuel injection system. A fuel pump that is faltering, providing low system fuel pressure/volume will cause hesitation. Your car's engine depends on constant fuel under pressure to supply the fuel injection system properly. Your car's fuel pump performs this action and is located in or near the gas tank. The injection system meters fuel through the injectors and into the engine. Many engine run drivability problems can be related to a weak or failing fuel pump. Problems can range from hard starting in the morning, low power and stalling while driving. Most vehicles have a fuel pressure test port somewhere on the fuel rail, use a flashlight to locate it on your engine or consult a car repair manual. Also test the fuel pressure regulator performance; if the regulator is stuck or leaking the engine will not receive the additional fuel needed for power. If the fuel system pressure is okay proceed to the next step.
Testing Fuel Pressure Video
Adjust the Distributor Ignition Systems - If your car engine has a DIS (distributor-less ignition system) skip this step. Ignition timing is very important in achieving maximum power from your engine with a hesitation. If the timing is adjusted too far retarded (behind the timing mark) in relationship to the engine crankshaft it will cause an engine to hesitate. To check your engines timing adjustment a timing light is needed. Once the timing light is hooked up to the battery locate the under hood emissions sticker that includes the engine timing specification and instructions. If you can't find the under hood sticker or it is illegible consult a car repair manual. If the engine timing is okay proceed to the next step. If the engine timing is way off (20 degrees or more) check the timing belt or timing chain, the crankshaft/camshaft correlation might be off. Checking the MAF, (mass air flow) and MAP (manifold absolute pressure) Sensors - The MAF or MAP help the PCM determine how much air the engine is consuming and distributes the proper amount of fuel. If these sensors become weak they can misread and cause the PCM to think the engine is turning slower than it is, in turn giving the engine less fuel and producing a hesitation. You might say wouldn't the computer see a problem and illuminate the service engine soon light? - MIL (malfunction inductor lamp) and the answer is not always. The computer PCM is designed to detect a shorted sensor or a sensor that is way out range. If the sensor is a little off but it is still within range the service engine soon MIL will not illuminate. This test procedure is simple but unique to each car, for this you will need a car repair manual. Check for Severely Worn or Mis-adjusted Spark Plug Gap - The engine timing is crucial to engine power output, if the spark plugs are severely worn or have a mis-adjusted air gap the timing of the spark can be delayed or ineffective. To check your engine's spark plugs wait until the engine is cold, then remove any spark plug and inspect. You are looking for the correct air gap between the electrodes, if the gap is incorrect remove all spark plugs and recheck. If the spark plugs are okay proceed to next step. Check the Timing Belt or Timing Chain Setting - The crankshaft and camshaft must stay in proper correlation. If this correlation is off the engine will hesitate. The procedure for checking crankshaft to camshaft timing varies on each car. You will need to gain access to the timing belt or chain marks. Once you have gained access check your timing marks here, timing belt or timing chain setting. Correct as needed and recheck engine, if the timing correlation is correct proceed to next step.
Transmission Clutch Problems - Sometimes the engine will have good power but it is not getting to the drive wheels. If you are driving and the engine sounds like it is working hard but the car is not going anywhere it could be the transmission clutch or clutches are slipping. When a clutch or clutches in a manual (standard) or automatic transmission wear they can slip not allowing the power from the engine to be transferred to the drive wheels and be lost due to lack of friction. In this case the only fix is to replace the clutch or clutches depending on automatic or standard transmission. If this is not the condition continue to next step. Harmonic Balancer to Crankshaft Timing - Some cars have an ignition trigger system that bases the engine timing off of the crankshaft harmonic balancer. If this balancer comes loose is can cause the keyway in the crankshaft to dig its way into the balancer causing the timing to retard which will cause engine hesitation. To check for this condition remove the harmonic balancer and inspect, replace if needed and reassemble.
If further assistance is needed, our certified car repair technicians are ready to answer your car questions. Related Car Repair Information
Failed Air Intake Boot
Replace Air Intake Video
Check Fuel Pump Pressure and Pressure Regulator - Fuel pump is worn providing low fuel pressure to the fuel injection system. A fuel pump that is faltering, providing low system fuel pressure/volume will cause hesitation. Your car's engine depends on constant fuel under pressure to supply the fuel injection system properly. Your car's fuel pump performs this action and is located in or near the gas tank. The injection system meters fuel through the injectors and into the engine. Many engine run drivability problems can be related to a weak or failing fuel pump. Problems can range from hard starting in the morning, low power and stalling while driving. Most vehicles have a fuel pressure test port somewhere on the fuel rail, use a flashlight to locate it on your engine or consult a car repair manual. Also test the fuel pressure regulator performance; if the regulator is stuck or leaking the engine will not receive the additional fuel needed for power. If the fuel system pressure is okay proceed to the next step.
Testing Fuel Pressure Video
Adjust the Distributor Ignition Systems - If your car engine has a DIS (distributor-less ignition system) skip this step. Ignition timing is very important in achieving maximum power from your engine with a hesitation. If the timing is adjusted too far retarded (behind the timing mark) in relationship to the engine crankshaft it will cause an engine to hesitate. To check your engines timing adjustment a timing light is needed. Once the timing light is hooked up to the battery locate the under hood emissions sticker that includes the engine timing specification and instructions. If you can't find the under hood sticker or it is illegible consult a car repair manual. If the engine timing is okay proceed to the next step. If the engine timing is way off (20 degrees or more) check the timing belt or timing chain, the crankshaft/camshaft correlation might be off. Checking the MAF, (mass air flow) and MAP (manifold absolute pressure) Sensors - The MAF or MAP help the PCM determine how much air the engine is consuming and distributes the proper amount of fuel. If these sensors become weak they can misread and cause the PCM to think the engine is turning slower than it is, in turn giving the engine less fuel and producing a hesitation. You might say wouldn't the computer see a problem and illuminate the service engine soon light? - MIL (malfunction inductor lamp) and the answer is not always. The computer PCM is designed to detect a shorted sensor or a sensor that is way out range. If the sensor is a little off but it is still within range the service engine soon MIL will not illuminate. This test procedure is simple but unique to each car, for this you will need a car repair manual. Check for Severely Worn or Mis-adjusted Spark Plug Gap - The engine timing is crucial to engine power output, if the spark plugs are severely worn or have a mis-adjusted air gap the timing of the spark can be delayed or ineffective. To check your engine's spark plugs wait until the engine is cold, then remove any spark plug and inspect. You are looking for the correct air gap between the electrodes, if the gap is incorrect remove all spark plugs and recheck. If the spark plugs are okay proceed to next step. Check the Timing Belt or Timing Chain Setting - The crankshaft and camshaft must stay in proper correlation. If this correlation is off the engine will hesitate. The procedure for checking crankshaft to camshaft timing varies on each car. You will need to gain access to the timing belt or chain marks. Once you have gained access check your timing marks here, timing belt or timing chain setting. Correct as needed and recheck engine, if the timing correlation is correct proceed to next step.
Transmission Clutch Problems - Sometimes the engine will have good power but it is not getting to the drive wheels. If you are driving and the engine sounds like it is working hard but the car is not going anywhere it could be the transmission clutch or clutches are slipping. When a clutch or clutches in a manual (standard) or automatic transmission wear they can slip not allowing the power from the engine to be transferred to the drive wheels and be lost due to lack of friction. In this case the only fix is to replace the clutch or clutches depending on automatic or standard transmission. If this is not the condition continue to next step. Harmonic Balancer to Crankshaft Timing - Some cars have an ignition trigger system that bases the engine timing off of the crankshaft harmonic balancer. If this balancer comes loose is can cause the keyway in the crankshaft to dig its way into the balancer causing the timing to retard which will cause engine hesitation. To check for this condition remove the harmonic balancer and inspect, replace if needed and reassemble.
If further assistance is needed, our certified car repair technicians are ready to answer your car questions. Related Car Repair Information