GM trucks falter on U.S. diesel: lawsuit

Plaintiffs allege fuel pump issue

General Motors’ line of diesel-powered heavy duty trucks are billed as workhorses, able to haul tens of thousands of pounds. Endless wells of torque from a 6.6-litre Duramax engine gets things rolling in a hurry.

However, a class-action lawsuit filed in Detroit seeks to put the brakes on certain models of GM’s heavy hauler, the Detroit News reports.

Plaintiffs allege problems with the powertrain’s high-pressure fuel pumps, units manufactured by Bosch and installed in Duramax-equipped trucks from the 2011 to 2016 model years. According to the suit, the pump introduced metal shavings into the fuel-injection system, leading to catastrophic and expensive damage.

GM and Bosch declined a request to comment by the Detroit News.

At the root of this issue, say the complainants, is the composition of American diesel fuel, which allows for less lubrication and eventual degradation of the Bosch pumps. Plaintiffs in the suit say once this happens, debris finds its way into the engine.

Modern diesel fuel is ignited under compression without a spark. A key indicator of diesel fuel quality is its cetane number, a measure of the fuel’s ignition speed. Diesel in Europe has a cetane rating of approximately 51, while U.S. diesel is generally rated around 45, except for a few areas in which a minimum of 48 is mandated (not to mention California, where diesel fuel has a cetane rating of 53).

For about the past 10 years, all American highway diesel fuel has been classified as Ultra-Low Sulphur Diesel (ULSD), a blend that lowered the measured sulphur content to less than 15 ppm. This, the suit claims, is the root of the problem.

The fuel pump used in the trucks in question, a Bosch CP4, was introduced in 2011. Plaintiffs claim it was designed for the European market and didn’t play well with American ULSD.

This may be so, but a smart lawyer might also note that the Duramax engines in question are not fitted with a lift pump. This is a bit of tech that takes some of the workload off the main pump; the Bosch CP4, in this case.

Without a lift pump, a low-pressure unit that pulls the fuel first, the CP4 is under constant suction and tasked with two jobs: drawing fuel and pressurizing it.

This situation may introduce air bubbles into the mix because the pump is located way up in the engine bay, which could help explain the production of metal shavings, which the suit claims are causing the expensive damage.

Driving.ca