The National Highway Traffic Safety Administration is investigating reports that some 2011-2013 model-year Ford F-150 trucks equipped with 3.5L-gasoline turbocharged direct injection (GTDI) engines have experienced incidents of diminished engine power during hard accelerations, the agency said.

Some owners have alleged that these unexpected, sharp reductions in engine power have occurred during hard acceleration while merging or passing at highway speeds.

NHTSA’s Office of Defects Investigation (ODI) has received 95 complaints, about one-third of which indicate the incidents took place while driving in humid or rainy conditions. No related crashes have been reported to ODI to date, however.

Ford has issued three technical service bulletins tied to intermittent stumble/misfire on acceleration from highway cruise in humid or damp conditions in some 2011 and 2012-model-year F-150 trucks equipped with 3.5L GTDI engines, NHTSA said.

The most recent bulletin includes procedures for first diagnosing a condition related to moisture accumulation in the charge air cooler, and then repairing the condition by reprogramming the powertrain control module with the latest calibration and installing a new charge air cooler and air deflector plate. The moisture in the charge air cooler can occur during extended highway cruising at constant throttle in humid or damp conditions.

The ODI’s preliminary evaluation will assess whether a safety-related defect exists.