Volkswagen recalls 170,000 diesels for mysterious fuel defect

Volkswagen said today it would recall nearly 170,000 diesel-powered Golfs, Jettas and Audi A3 to fix a fuel line that could leak. What makes it more interesting is just how hard VW had to work to find the defect.

The recall affects 2009-2012 models of Jetta sedans and wagons, along with 2010-2012 Golfs and A3s all built with the 2-liter TDI diesel. No reports of fire or injuries have been reported from the defect, and Volkswagen expects that less than 1% of the cars covered by the recall will show signs of the defect — although 20% may have the broken parts.

The problem began in February, when VW received a few reports of fuel leaking in engines from dealers performing warranty repairs. Fuel leaks are serious enough in general, but they take on an added urgency in high-tech diesels like the 2-liter TDI, where fuel is directly injected into the engine at pressures of up to 26,000 psi. Even a tiny leak at those pressures can spew a lot of flammable liquid quickly.

But VW's engineers were puzzled; after a few months of tests, they could find no reason why the fuel lines should be leaking. Compounding the issue: The reports were coming only from the United States, not the same engine sold in Europe. Injector tubes from one supplier had some scratches, but nothing that would lead to cracks on its own.

All of those details turned out to be clues to the real problem. To meet U.S. emission requirements, the TDI engine computer pulses the flow of diesel fuel differently than in European editions. Every so often, those pulses would vibrate the scratched injector on the second piston in just the right frequency to slowly create a crack, and over time, a leak.

This is why everyone isn't an engineer.