This applies to VW pump duse TDI engines, I thought the group might find this interesting. The 04 to 06 VW tdi's have been known to wear the lobes off their camshafts, usually as a result of not using the proper 505.01 spec engine oil. The first warning sign is usually soot in the air filter, but no particular driveability symptom. [2006 Volkswagen Jetta TDI, Engine/Propulsion Photo] [2006 Volkswagen Jetta TDI, Engine/Propulsion Photo] This could be picked up at a routine service. As one or more exhaust lobes on the camshaft begins to wear, lift is reduced, but the exhaust valve still opens. No noise is present because the engine has hydraulic lifters (with remarkable ability to pump up and maintain valve clearance). As the condition deteriorates, sometimes odd MAF codes are stored, "implausible signal" etc. Exhaust cannot exit the cylinder fully because the valve is barely opening, so there is some reverse flow into the intake the next time the intake valve opens. It all hits the fan once the top of the lifter gets a hole worn through it. At that point the lifter collapses and the exhaust valve doesn't open at all. The four stroke cycle becomes three- intake, compression, power, and nowhere to go........ followed by pow! back through the intake plumbing and intercooler. Here are pics of a worn cam lobe and a relatively good lobe [2006 Volkswagen Jetta TDI, Engine/Propulsion Photo] [2006 Volkswagen Jetta TDI, Engine/Propulsion Photo] The car in question actually drove in with almost 1/4 inch of lift missing from an exhaust lobe and was backfiring into the intake when given throttle. If you see significant soot in the air filter, you may want to suggest inspecting the camshaft before broken pieces of lifter start floating around.

John from Ontario

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