America's Nasty Diesel Fuel Keeps Ruining Bosch Fuel Pumps

The National Highway Traffic Safety Administration (NHTSA) is upgrading its ongoing investigation into a rash of failures of high-pressure fuel pumps affecting diesel-powered Ram, Jeep and BMW vehicles. Nearly 500,000 vehicles could be affected, and so far, the working theory is that these fuel pumps, supplied by Bosch, are failing because of America’s garbage diesel fuel.

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Automotive News brings us the latest on the fuel-pump mystery. According to documents published by NHTSA this week, and viewed by AutoNews, NHTSA’s Office of Defects Investigation is expanding a probe into automotive component supplier Robert Bosch, based on an investigation that began in October 2021 involving 2019 and 2020 model-year Ram 2500, 3500, 4500 and 5500 trucks powered by the Cummins 6.7-liter turbodiesel inline-six.

Those Ram models were prone to exhibiting stalling or loss of power, attributed to malfunctions in the high-pressure fuel pump. And along with upgrading the investigation to an “engineering analysis” — another step on the path to a full recall — NHTSA added a bunch of other vehicles to the list: diesel-powered 2014 through 2022 Ram 1500s, 2021-2022 Jeep Gladiators, 2014-2020 Jeep Grand Cherokees, 2020-2022 Jeep Wranglers, as well as diesel-powered BMW 3-series, 5-series, and X3 models from 2014 through 2018. Automotive News reports that as many as 490,000 vehicles could be affected if the engineering analysis is expanded into a full recall.

As AutoNews reports, when NHTSA reached out to BMW, the automaker “indicated that failed pumps on their vehicles were caused by an interaction between pump internal components and U.S. market diesel fuel, leading to increased slip and eventual particle-generating wear surface.”

See, while the United States recently switched to Ultra Low Sulfur Diesel in 2011, our modern diesel still lags behind what folks can buy in Europe. As explained by Hot Shot’s Secret — a company selling diesel fuel additive aimed at folks who make a living driving diesel vehicles — American ULSD can have up to 15 parts per million sulfur, compared to Europe’s 10 ppm max.

More importantly, U.S. diesel fuel just doesn’t have the same lubricity as the European stuff. As Planet Safe Lubricants (which sells nontoxic industrial grease) explains, lubricity is tested by running a standardized test where a ball bearing is scraped back and forth on a metal surface for 90 minutes, while bathed in the fuel or lubricant being tested. At the end of the test, scientists measure the size of the “wear scar” (in other words, the flat spot) that’s worn onto the ball bearing. A bigger flat spot means the diesel fuel being tested does a poor job of lubricating moving parts — as you’d want it to do inside a high-pressure fuel pump.

Here’s the (literal) rub: European diesel fuel specifies a wear scar of 460 microns; U.S. diesel fuel allows a larger wear scar of 520 microns. Thus, the diesel that comes out of American fuel stations does a poorer job of lubricating moving parts.

That’s the theory behind all these Bosch fuel pump failures. As Hot Shot’s Secret pointed out in 2020, a slightly different Bosch diesel fuel pump was showing a failure rate of around 7 percent in the U.S., compared to 1 percent in Europe. Now, NHTSA seems to be preparing for a potential recall on a whole slew of Stellantis and BMW vehicles plagued by a similar problem — one that all comes down to America’s nasty diesel.

via CarScoops