United States v. Pierce Diesel Performance, et al.

On August 6, 2025, a court sentenced Jeremy Pierce and his company, Pierce Diesel Performance, to jointly pay a $375,000 fine and complete three-year terms of probation. Pierce pleaded guilty to a felony violation of the Clean Air Act for tampering with a monitoring device (42 U.S.C. § 7413(c)(2)(C)). Pierce Diesel Performance pleaded guilty to conspiracy to violate the Clean Air Act (CAA) for providing technical support to customers nationwide who purchased tuning devices and tunes from his brother Barry Pierce's company, Gorilla Diesel Performance (GDP) (18 U.S.C. § 371).

A court sentenced Barry Pierce and his companies, GDP Tuning and Gorilla Performance, in July 2024, after they pleaded guilty to conspiracy and violating the CAA (18 U.S.C. § 371; 42 U.S.C. § 7413). Pierce served four months’ incarceration, with one year of supervised release. GDP Tuning and Gorilla Performance are completing five-year terms of probation. All defendants were ordered to jointly pay a $1 million fine.

The U.S. Environmental Protection Agency Criminal Investigation Division conducted the investigation.