Occasional full-throttle stomp good for turbocharger

In this story from the world of auto repair, automotive technician Nick Labrie explains about a customer who arrived in a Volkswagen Jetta, which had recently come down with symptoms including poor performance, an erratic idle, bad mileage, and a check-engine light.

The vehicle’s owner had their friend perform a diagnostic scan on the vehicle, which revealed a stored ECU trouble code for an ‘overboost’ condition, which referenced a problem with the turbocharger. “He expected the worst, having convinced himself that the turbocharger was finished, and that it would require an expensive replacement,” Labrie said. “Thing is, the vehicle only had about 240,000 kilometres. We typically see these Jetta’s rack up plenty more miles than that before any serious issues, if at all.”

The owner was worried about the potentially-pricey bill for a new turbocharger. But, given the age of the vehicle, the problem described and the initial diagnostic scan results, Labrie had a hunch.

Labrie believed that the problem lay with the turbocharger’s wastegate. That wastegate is a mechanical component used to control turbocharger boost pressure. In simple terms, it consists of a metal rod that opens a small ‘trap door’ inside of the turbocharger. That trap door bleeds extra exhaust gas out of the turbocharger to help limit turbocharger boost pressure levels. The metal rod opens the trap door when pressure is applied, and keeps boost levels from exceeding a certain limit set at the factory. “Sometimes, the wastegate assembly seizes up when it gets old. When that happens, the turbocharger can’t control its boost, and the boost gets too high, and a check-engine light comes on, and the engine goes into limpmode,” Labrie said.

The vehicle didn’t need anew turbocharger, it just need-ed a new wastegate. But Labrie, trying to save his customer some cash, had an even

cheaper solution. “I pulled apart the accessible parts of the wastegate assembly, dismantled those, cleaned the rust off with a wire-wheel to smooth the surfaces, lubricated them really generously and put them back together,” he said.

The reason the wastegate failed, according to Labrie, is an interesting one, caused by the owner’s driving habits. “We had a little chat about the owner’s driving, and I asked him, how often he opens the engine up,” Labrie said, adding that the wastegate assembly moves fully, only when drivers apply moderate to heavy throttle, though this owner admitted to driving the car gently at almost all times, and never giving it much pedal. “Because this car was driven by light-footed drivers, the engine rarely works hard and the turbocharger rarely works hard, which means the wastegate rod rarely moves through its full range of motion, if at all.”

“It’s one of those things where, occasionally, a good full-throttle blast can be helpful. Just like people, some car parts get stiff and seized if they don’t move for a long time”. All said, as Labrie’s latest customer learned, in some situations, a bit of fullthrottle acceleration might save you a trip to the shop.