Skip the auto shop - Our mechanics make house calls

Q: Engine stutters under load in high gear.

asked by on

My 1997 F250 7.5L (460) gasoline engine stutters when pulling hills (or under load) in high gear. This is the 5-speed manual transmission 4x4 HD model. There is no change in engine sound, just a hitch that can be felt. I have replaced the distributor cap, rotor, wires, and plugs as well as the fuel filter. Any suggestions?

My car has 102000 miles.
My car has a manual transmission.

This may be a sign of a faulty MAP sensor as the vehicle responds adversely to a load put on the motor (i.e. putting it in gear or engaging the brakes). The Manifold Absolute Pressure (MAP) sensor senses engine load and generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment. When the engine is working hard, intake vacuum drops as the throttle opens wide. The engine takes in more air, which requires more fuel to keep the air/fuel ratio in balance. When the computer reads a heavy load signal from the [MAP sensor]((https://www.yourmechanic.com/services/manifold-absolute-pressure-sensor-map-sensor-replacement), it adjusts the fuel mixture to slightly more rich than normal so the engine can produce more power. The computer will then retard (back off) ignition timing slightly to prevent detonation that can damage the engine and decrease performance. This may also be caused by other closely related components such as a dirty or failing mass air-flow sensor, a faulty throttle position sensor or potentially a vacuum leak. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: 97 Ford F-150 won't start after 30 minutes of driving wait 30 minutes and start I'll change the coil pack spark plugs wires

Hi There, If I understand correctly, you have already changed the coil packs which is a good first step as this is a common indicator based upon what you are describing. Other things that you may want to also check...

Q: Serpentine belt constantly slips off

Hi. Most likely there is something out of alignment in your pulley system causing the belt to come off. The first thing to inspect would be the idler pulley. Remove the belt and check if the pulley wobbles. If so,...

Q: Truck barely moving in lower gears

Hi. It sounds like your transmission fluid may just be dirty. Dirty transmission fluid can cause the car to hesitate. Check your owner’s manual to see how much transmission fluid is supposed to be used. In most circumstances changing the...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.