In another instance of, "How is this still happening?" Ford is being accused of conspiring with Bosch to make cheat-y diesels for the US market.

The class-action lawsuit brought by F-250 and F-350 owners alleges that Ford and supplier Robert Bosch GmbH worked together to mask the nitrogen oxides and particulate emissions of F-Series Super Duty diesels built between 2011 and 2017, in violation of the Clean Air Act. The suit goes on to claim that Bosch software allowed Ford to alter engine parameters to help achieve optimum emissions during EPA testing, but in the real world, the engines produced more power with less fuel while emitting over 50 times the legal limit of greenhouse gases and particulate matter.

Enlarge Image Ford

If this sounds familiar, it should. It's essentially the same trick that Volkswagen admitted it pulled on 500,000 TDI models, which led to $24 billion in fines. The alleged Ford cheating is also on that scale, and this kind of lawsuit definitely does not bode well for the Blue Oval on the eve of the launch of a diesel-powered F-150.

The lawsuit, announced by Bloomberg, accuses Ford and Bosch of 58 violations of state consumer law, false advertising and racketeering. It should be noted that Ford isn't alone in being accused of diesel cheating. Both General Motors and Fiat Chrysler have been the target of similar allegations, though they aren't named in this particular suit.

"Bosch takes the allegations of manipulation of the diesel software very seriously. It is a well-known fact that these allegations remain the subject of investigations and civil litigation involving Bosch," said Alissa Cleland, spokesperson for Robert Bosch LLC, in a statement to Roadshow. "Bosch is cooperating with the continuing investigations in various jurisdictions, and is defending its interests in the litigation."

Ford is flat-out denying the allegations put forward in the lawsuit. "All Ford vehicles, including those with diesel engines, comply with all U.S. EPA and CARB emissions regulations. Ford vehicles do not have defeat devices. We will defend ourselves against these baseless claims," said Mike Levine, product communications manager for Ford North America, in a statement to Roadshow.

From 1994 to 2010, Ford sourced its Power Stroke diesel engines from a company called Navistar. Navistar used to be called International Harvester and built cool SUVs like the Scout, but now, it makes medium and heavy-duty trucks, chassis and diesel engines. In 2011, Ford brought the design and manufacture of its diesel engines in-house, starting with the 6.7-liter "Scorpion" engine.

Enlarge Image Joseph Brent

Diesel engines are naturally more fuel efficient than gasoline engines of similar displacement, and are capable of producing vast amounts of torque, both traits that make them ideal for trucks like the Ford F-250 and F-350 Super Duty. This why Ford was able to offer the 6.7-liter Scorpion engine with a warranty, despite producing in excess of 800 pound-feet of torque. Where diesel often falls down is in the emissions department.

Diesel is a less-refined fuel than gasoline, and as such, it has more impurities. It also tends to create a great deal of soot, otherwise known as particulate matter (e.g., the gross black clouds one gets when "rolling coal") and nitrogen oxides. Taming these while remaining powerful and efficient has been a serious challenge, hence the alleged cheating.

Typically, the exhaust path for a modern diesel would go from the cylinders to a particulate filter, then to the catalyst and finally, a urea injection system would treat the spent gases before being sent out the tailpipe. Ford changed this around to make more power. It sent the dirty exhaust gas through the catalyst first, put the particulate filter next and finished with urea injection. Except, after being catalyzed, Ford is accused of bypassing the particulate filter and dumped the unburnt particulate out the tailpipe.

The continued revelations regarding diesel emissions cheating are truly unfortunate, not only because they represent a serious breach of trust between customers and the manufacturers of these vehicles, but because of the likely irreparable damage they have caused to the image of diesel vehicles in America.