The government estimates around 400,000 F-150 pickups from the 2011 through 2013 model years are involved.
The National Highway Traffic Safety Administration has received 95 reports of engines losing power during hard acceleration, such as when passing. The incidents often occurred in rainy or humid weather. NHTSA has no reports of crashes or injuries.
NHTSA says Ford told dealers how to fix the issue but hasn't alerted owners. NHTSA investigations often lead to recalls.
Ford owners in Ohio and Louisiana recently sued Ford in federal court, claiming the EcoBoost engine is defective because it loses power during acceleration.
The Dearborn, Mich., automaker says it's cooperating with the investigation.