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PD Tdi: 2004 Mark IV: Pumpe Duse Injection

Gear case (3)The BEW and BRM PD Tdi series was a radical change in injection technology in diesel engines. PD, or Pumpe Duse, refers to the injectors, which are in effect the final diesel pumps. The injectors are now inside the cylinder head, with electronic controls in the injectors themselves. An extra lobe on the camshaft operates the injectors via a roller bearing rocker arm. The fuel is first pumped out of the tank with a small electric fuel pump at 4 to 11 psi, depending on volume. A tandem pump on the end of the cylinder head raises the fuel pressure to 45 to 115 psi to feed the injectors, depending on the engine rpm. The injectors are electronically controlled to vary the fuel volume, and to vary the fuel pressure from about 8000 psi to over 27,000 psi. Higher pressure means better atomization, which yields a more efficient explosion. The PD Tdi thus increases power while using even less fuel.

The electric fuel pump in the tank can fail and starve the tandem pump on the head. The tandem pump is so named because it pumps fuel and also pumps the vacuum for the brake booster. A starving tandem pump will then cavitate, causing potential power loss. Cavitation makes bubbles which are actually vacuum pockets that fill with the vapor of the fluid. There is no filtration between the tandem pump and the injectors. Extreme cavitation can cause the tandem pump to grind up, shedding metal flake into the injectors. Cavitation can make bubbles at faster than the speed of sound, which can rip metal off the surface. A boat engine that radically overpowers the propeller can cause the propeller to shed metal, and it eventually looks like it was blasted with a shotgun. The same thing can happen to your tandem pump. Replacing injectors and the pump runs mega dollars. Learn to listen for the quiet pump turning on with the key for two seconds. I did say the quiet word. Have your technician test your pump periodically. We do that every time we replace a fuel filter at Karmakanix.

With the injectors moved from the front of the head to the inside, the installation angle of the glow plugs was changed to directly vertical. This allowed the electrical harness to be removed without pulling slightly sideways, and the harnesses got damaged and replaced less frequently. Midway through the PD Tdi series, the glow plugs went from a 12 volt to a variable voltage design. This proved a great improvement that reduced their failure rate.

The PD Tdi has an active throttle body. The earlier Tdi’s had a throttle flap that just slammed closed when you turned off the engine to prevent the vibration of the engine winding down from shaking the car. The PD throttle body can close partway in front of the new electronic EGR valve to allow exhaust gases to be recirculated while the engine is under partial load and boost. The later BRM also introduced the hot and cold running EGR system. Hot EGR to help warm up the engines. Think Freezy Germany. Cold EGR to keep the intake manifold temperatures down, using the same old EGR cooler as the previous engines.

With the second PD Tdi motor, The BRM of the 2006 Jetta, the turbocharger got a sensor on the wastegate for more precise control. No doubt the boost control got better, but it also got a brand new symptom if the turbocharger started to stick. Older models would overboost when the wastegate was sticky at full boost, and the engine control unit would just drop power to 40% to save the ship. The BRM can have this same issue, but the wastegate can also stick at the lower stop and cause an even more alarming problem. This BRM turbo failure mode would cause extreme rich conditions with vast amounts of black smoke and nailing. Basically, the ECU would cause the injectors to dump in so much fuel that much of the excess did not evacuate during the exhaust cycle, and would then combust prematurely during the next compression stroke. Meanwhile the DSG transmissions would beat the clutches and flywheels to death.

The timing belt system was changed, it is much more reliable and is way less prone to failure. Variable tooth spacing on the crank drive gear better matches the belt teeth at the moments when the cam pulls the hardest, stretching the belt. A vibration damper in the cam gear and a hydraulic tensioner were added. The timing belt and gears got 5mm wider. The belt is shorter and the pathway straighter, with greatly reduced angular changes in the pathway.

The timing belt job got a little easier, but the tradeoff was that you needed another batch of special tools, and you could not monitor the engine timing with VAG COM on your laptop. If a timing belt breaks, the most reliable fix is to replace the camshaft and lifters. The camshafts on these PD Tdi motors sometimes wear out and wear right through the lifters. It is a hardening problem, and it happens within a thousand miles once the problem starts, often while traveling long distances. Because a timing belt failure bangs up the cam as it bends valves, the safe thing to do is the Full Monty. Very expensive, don’t drop that belt and crash that motor.

Karmakanix is experiencing an increasing number of the camshaft and lifter failures due to wear. To squeeze in the cam lobe that runs the injectors, the cam lobes for the valves got thinner. The height of the lobes was increased to maintain surface contact area, but the friction surface speed increased radically. This produces higher temperatures that can actually boil the oil inside the lifters. The slight bit of oil vapor allows the lifters to chatter, as there is a pneumatic effect much like a spring. This produces a wear pattern known as Starburst, and the surface wear is accelerated. The surface hardening of the camshaft and lifters is just a few thousandths of an inch thick, and once the process starts, wearout can occur in just a few thousand miles or less. We believe that the wear reduction from Molybdenum Disulfide additives may be the extra protection all of these Pumpe Duse series engines require to avoid the camshaft and lifter wear problem. Karmakanix recommends the use of Liqui Moly MoS2 additive every 4th oil change.

As these engines get older, we are finding an increasing number of camshaft failures. Karmakanix recommends that the camshaft be inspected prior to timing belt replacement on engines with over 200,000 miles. It is a fairly simple matter to remove the valve cover for inspection, and we just want to avoid having to repeat most of the same labor.

Unlike previous engines, these PD Tdi diesel injection systems have a fuel cooler with a thermostat mounted underneath the car on the right side amidship. It is like a little radiator, and is required because the fuel moves through the head and can exit almost boiling. The fuel must be cooled before it gets back to the tank. The fuel cooler is not covered, but does not hang down low. Nonetheless, be cautious when driving on rutted dirt roads, we have seen them damaged at Karmakanix, but we have not seen one leaking yet.

Gear case (2)Karmakanix Knowledgebase Information on PD Tdi Camshaft Replacement

Gear case (3)