The University of West Virginia researchers who uncovered Volkswagen's diesel cheating scandal have released test results showing that diesel-powered Fiat-Chrysler vehicles spewed as much as 20 times the legal emissions level, Bloomberg reports.

The university's Center for Alternative Fuels, Engines and Emissions released the results about a month after the U.S. Justice Department accused FCA of using a defeat device to evade emissions testing. FCA has adamantly denied the claim.

In a June 13 statement, FCA said the center's testing "appears to have been commissioned by a plaintiffs’ law firm for purposes of litigation." Researchers have declined to reveal who funded the testing. The center has been "unwilling to discuss the report" with FCA, according to the automaker.

The center tested the vehicles on roads, while the Enviromental Protection Agency tests vehicles in a laboratory using a dynonometer. FCA questioned the tests, saying they were done at speeds of more than 50% greater than the EPA with 600 to 700 pounds of payload, and on grades. Any comparison to EPA testing would be "invalid," FCA said.

Daniel Carder, the center's director, acknowledged to Bloomberg that his tests were more demanding but said even though an engine works harder on a steep ascending road, emissions can be lower due to the way exhaust treatment systems work.