NHTSA Engineering Analysis EA23002: Loss of Motive Power
On July 22, 2022, the Office of Defects Investigation (ODI) granted a Defect Petition (DP22001) and opened a Preliminary Evaluation (PE22007) to investigate allegations of loss of motive power in model year (MY) 2021 Ford Bronco vehicles equipped with 2.7L EcoBoost engines. Complainants were reporting sudden engine failure while driving resulting in a loss of motive power, often without the ability to restart. During PE22007, the cause of engine failure and loss of motive power in the subject vehicles was determined to be intake valve fracture, and the full scope of vehicles affected by the subject defect was identified as all MY 2021-2022 Ford and Lincoln models equipped with either the 2.7L or 3.0L EcoBoost engines, referred to as the “Nano” engine family. If an intake valve fractures in the subject engines, it may drop into the cylinder and contact the piston, often resulting in catastrophic engine damage. On September 29, 2023, PE22007 was upgraded to an Engineering Analysis (EA23002) to further investigate the subject defect across the full scope of affected vehicles. During EA23002, ODI visited Ford facilities to review technical information related to intake valve fracture in “Nano” engines, coordinated with NHTSA’s Vehicle Research and Testing Center (VRTC), and analyzed updated field data relating the subject defect. Forensic analysis of fractured intake valves demonstrated that the defective components exhibited “grinding burn” or out of specification hardness in the area of the keeper grooves. The presence of grinding burn is evidence that during the groove grinding phase of production, the temperature of the valve became sufficiently high to alter the microstructure of the material and is indicative that the valve supplier’s manufacturing processes were not within control specifications. Grinding burn results in a hard, brittle microstructure and high residual stresses toward the surface of the valve. Through normal engine loading, a valve with grinding
US National Highway Traffic Safety Administration