First to recognize the problem, realize that this issue refers to the first two engines in the Stratified Injection series. It does NOT include the later TSI engines. The factory upgraded the engine design to eliminate the problem by driving the high pressure pump directly off the end of the camshaft, eliminating the oscillating lifter on cam lobe design. The camshafts of the first two earlier motors which start in 2005 have a three pointed lobe on the end of the camshaft that drives a small lifter connected to the high pressure fuel pump. Other motors have 2 or 4 pointed cam lobes. Some might comment that the wear out problem was not entirely unexpected, since the lifter and cam lobe are proportionally small to the lobes and lifters that push on the intake and exhaust valves, the lobe ramps are somewhat steep, and it works the pump 2 to 3 times per turn instead of once per turn of the camshaft. And pumping fuel up to between 725 to 2175 psi is not an easy chore. It seems that the three lobe cam system is the most prone to failure by far.
The problem manifests itself as inefficient and insufficient injection quantity, and generally gives a Diagnostic Trouble Code (DTC) for secondary injection pressure. At Karmakanix, we like to take a quick tour through some essential Measuring Block Values (MVB) to check the health of these early systems. One gives the power percentage to the electric primary fuel pump in the tank. Percentage figures above 55-60% generally indicate a clogging fuel filter, which will eventually lead to an overheated and failed fuel pump. They can also indicate a failing fuel pump or a bad power supply module. Of interest to this page however are the MVB’s about the secondary pressure. The secondary pump regulates pressure by opening and closing the valves inside it at precise camshaft angles, cycling once per cam lobe. When the total angle exceeds certain values, it is likely that the cam lobes for the secondary pump are wearing out, and complete demise happens fairly rapidly. Both the cam lobe and the lifter suffer simultaneously.
As with all cams, the surface is quite hard, but progressively softer as one goes deeper. This results from the case hardening technique during manufacture. The cam billets are heated to a yellow hot glow, then rapidly quenched in water or oil to cool at a specific rate, hardening the exterior. A complete article is available on Wikipedia.
We have seen engines have the cam lobe problem more than once. Pictured is a cam gear that was forced into place during a repair, breaking the dowel pin and damaging the new cam. The shop shall remain unnamed, let’s just say it was the most expensive place to get your car repaired. The car left with the cam out of time, which likely had no bearing on the second wearout. And other second time repairs have occurred. Many cam and lifter jobs were done fairly early in the engine’s life, and were covered by the extended warranty. As the cars get older, the problem has not stopped, but the customer now has to foot the bill.
The obvious question becomes whether the key is metallurgy or maintenance. Karmakanix urges customers to adopt a 5000 mile oil change interval instead of the factory 10,000 mile requirement. We also highly recommend using a Molybdenum Disulfide additive such as Liqui Moly MoS2 to help prevent the wear from starting in the first place. We suggest including the additive with each major service, as it is only necessary to treat the engine about every fourth oil change.