Engine Hesitation at Highway Speed – Reasons and Fixes
Finding yourself struggling to accelerate and merge onto the highway can be an unnerving and unsafe experience for drivers. Engine hesitation at highway speed or stumbling issues when trying to speed up to highway speeds is caused by a variety of mechanical faults in systems like fuel delivery, spark ignition, sensors, and more. Understanding the root causes along with available solutions empowers drivers to get prompt repairs and restore confidence for highway driving once again.
Failing Fuel Pump Unable to Keep Pace
One of the most widespread reasons an engine experiences dramatic losses in power and acceleration capability at highway speeds points to a failing fuel pump. This crucial component is tasked with supplying the correct volume and pressure of fuel to the injectors as demands increase. However, aging fuel pumps eventually wear out and cannot maintain adequate fuel force under hard acceleration needs leading to engine hesitation at highway speed.
Symptoms of a failing fuel pump struggling to keep up with engine fuel demands manifest as abrupt losses in acceleration capabilities between 40-60 mph. Other indicators include loud whining noises emanating from the tank indicating excessive pump strain. Outright fuel pump failure results in a no-start condition as the engine receives zero fuel.
Replacing the fuel pump requires safely raising the vehicle to access the tank and pump housing. Once disconnected, the new unit can be installed matching OEM specifications for that engine. Road testing post-replacement will quickly reveal if fuel pressure and volume have been restored. When acceleration hesitation issues completely disappear after pump replacement, technicians confirm the root cause of engine hesitation at highway speed.
Dirty Fuel Injectors Unable to Properly Atomize Gasoline
The high-pressure fuel injectors must blast gasoline into a fine mist to mix properly with incoming air. When these precision components become fouled with internal build-up and deposits, their ability to correctly atomize fuel becomes degraded. Poorly atomizing injectors deliver an improper air/fuel ratio under acceleration demands leading to engine hesitation at highway speed. This imbalance in the combustion mixture brings about flat spots, hesitation, and significant power losses as engine rpm climbs.
Every make and model utilizes slightly different symptoms and testing procedures to accurately pinpoint dirty or clogging injectors:
- Scan tool fuel trims displaying rich bank faults hint at dirty injectors struggling to atomize fuel causing engine hesitation at highway speed.
- Individual cylinder acceleration tests help narrow down one or more problem injectors.
- Pressure testing fuel rail detects uneven returnless system fuel pressures from dirty units.
- Power balance tests identify cylinders down over 15% on power due to fuel delivery issues.
Once identified, specialized fuel injector cleaning machines can restore dirty units to proper operation. These machines flush internal components and use potent detergents to dissolve harmful carbon deposits and varnish buildup. Just 15 minutes of professional cleaning clears out blocked passageways and orifices so spray patterns markedly improve. Properly atomizing fuel injectors cure acceleration problems plaguing dirty units leading to engine hesitation at highway speed.
Ignition Coils Unable to Ramp Output at Higher RPM
The ignition coil pack is made up of multiple coil assemblies responsible for ramping up voltage to extreme levels needed to fire the spark plugs. Acceleration demands increased spark energy which borderline coils cannot supply adequately at higher RPM ranges leading to engine hesitation at highway speed. This results in occasional cylinder misfire events that bring about dramatic losses in engine power as rpm climbs.
Warning signs of failing ignition coils about the be pushed beyond their operating capacity manifest as check engine lights with cylinder-specific misfire codes stored. Engine scanner live data may reveal certain cylinders dropping out intermittently above 3000 RPM. Strange odors, loss in mpg figures, and elevated hydrocarbon emissions trip diagnostic monitors impacted by misfires causing engine hesitation at highway speed.
Testing ignition coil pack output requires reading primary and secondary resistance values with a DVOM. Key checks for faults in coil windings or arcing at boot terminals. Using an engine diagnostic oscilloscope tests for sufficient coil kilovolt outputs under simulated acceleration events. Mechanics replace coils well below 15 kilovolts peak energy at 5000 rpm.
Swapping borderline coil packs for robust aftermarket upgraded ignition coils effectively eliminates misfires related to insufficient ignition spark energy. New coil packs in particular correct slow acceleration issues restoring performance characteristics. Healthy ignition means confident smooth acceleration critical for highway merging safety without engine hesitation at highway speed.
References:
- “Fuel pump”. Wikipedia. https://en.wikipedia.org/wiki/Fuel_pump
- “Why Does My Car Hesitate When I Hit the Gas?” https://www.carfax.com/blog/hesitation
