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Camshaft timing (torsion value) adjustment on VW and Audi PD TDI engines
How to fine tune camshaft timing (torsion value) on PD TDI engines
If you're not sure if your engine is pumpe duse, see 1000q: pumpe duse vs. common rail and direct injection. All TDI model year 2004 -2008 sold in North America were pumpe duse. The crankshaft (which moves the pistons) uses a timing belt to drive and precisely time the camshaft (which opens the valves). While the solenoid which allows fuel injection is electronically controlled by the ECU and injector solenoids, the pressurization of the pumpe duse injectors is mechanical and by the extra camshaft love found on unit injector (pumpe duse) engines. The camshaft sprocket has an adjustment range to adjust torsion or idle stabilization. This adjustment can drift over the life of the timing belt on pumpe duse TDI engines which is a common cause of rough idling and hard start. In North America, pumpe duse engines include the 2004-2006 Golf, New Beetle, VW Jetta TDI and 2004-2005 Passat TDI. It also includes the V10 Touareg TDI but it used a gear drive for the camshaft and not a timing belt. Europe also had some DOHC TDI engines which are slightly different.
A 2006 VW Jetta TDI is shown but other SOHC engines are the same.
While this may fix your rough idling, a rough idle on pumpe duse engines could also be caused by worn camshaft lobes. This was a common problem on pumpe duse TDI due to their narrow lobes. See 1000q: TDI camshaft inspection and replacement for PD engines for details. It could also be caused by faulty and unbalanced fuel injectors. The procedure for inspecting is seen below. Lastly, the dual mass flywheel could be bouncing around and causing the rough idle. See 1000q: clutch FAQ for more details. DSG automatics seem to have more problematic DMF. See 1000q: DSG FAQ for more details. General running problems could be caused by a boost leak so make sure there are no air leaks in the intake path. See 1000q: boost leak check for more details.
Checking or adjusting torsion will also give the best results after doing a timing belt job on these engines. Once the timing belt is 60-80% through its scheduled replacement interval, check it again and adjust it as necessary. Proper timing will give the least vibration at idle and give easier starting. This is not a substitute for using the special VW/Audi timing belt tools. See the timing belt articles linked below for your engine for details. The point of the camshaft pin and the hole in the toothed window on the camshaft sprocket is to get timing to where the engine will start fine and be about right, as a rough estimate, +/- 1 degrees. If you don't have access to a VCDS, just find someone later who can help you and do it when practical.
Basic explanation of the PD fuel injection
The camshaft pulley/hub (under the sprocket which the timing belt rides on) has bent tabs on the edge of the pulley, shown in the below picture. These tabs pass by the camshaft sensor and let the car's computer know exactly where the camshaft is. There's a key on the camshaft pulley which indexes its position to the camshaft so the relationship between the tabs and the camshaft position is fixed. Rotating the camshaft and pulley not only changes mechanical operation of the valves but lets the car's computer see a change in camshaft timing which can affect fuel injection timing in relation to the piston stroke. There is another sensor which reads the crankshaft position.
As the extra lobe on PD camshafts moves the rocker, the rocker pushes on the fuel injector plunger. The car knows when this should be happening because of the camshaft sensor. This also assumes the injector rocker pin and lock nuts are set correctly. The ECU then tells the solenoid (or piezo element in newer PD engines not sold in North America) on each fuel injector to close. The restriction creates a buildup in fuel pressure inside the injector. The fuel pressure lifts a mechanical needle which sprays a pilot injection and then a main injection. The fuel injection stops when the solenoid opens and fuel pressure drops inside the injector, causing the springs to close the needle. If the solenoids are disabled and off, like when you unplug the round plug on the cylinder head for the injector wiring harness and crank the engine, the fuel will not build up pressure since the solenoid isn't closing.
Timing belt articles
1000q: 2004-2005 Passat TDI timing belt part 1, BHW engine
1000q: 2004-2006 Golf/New Beetle and 2004-2005 Jetta TDI timing belt removal, BEW engine
1000q: 2005.5-2006 VW Jetta TDI timing belt replacement 1, BRM engine
torque wrench (required, see 1000q: torque wrench FAQ for a basic intro to torque wrenches)
computer and VCDS software and cable (required)
Note - if you just replaced the timing belt, first do all final checks, start the engine, and check fluid levels before doing this procedure.
If you didn't just replace the timing belt or you're ready to start, drive the car until it's at normal operating temperature. With the headlights/fan/electrical load off, plug the VCDS cable into the obd2 port and start the software. Click on the "Engine" button to enter the engine module.
Your controller part number may vary by year/engine. Click on "Meas. Blocks".
Then click "Up" 4 times or enter 4 to view Group 004. The number on block 4 is labeled "Torsion Value". Higher than 0 is advanced timing and lower than 0 is retarded timing. The best value is about 0-0.5. The Passat TDI appear to like about 0-0.5. Jetta TDI appear to like .5-1.0. A little higher by 0.5 is fine because torsion tends to slightly retard as the belt ages. More advanced than 1.0 may give best results in your case and adjusting the torsion by +/- 1.0 won't cause any damage, so feel free to play with the value.
While you're here, also check the idle stabilization through injection quantity (measuring block group 13). The car's computer can adjust the amount of fuel injected to stabilize idle. A value more than +/- 0.5 would indicate a problem. You could try filling the fuel filter with a can of diesel purge and running it like that to clean out the injectors.
Shut off the engine and the car. Take care when working on the engine since it will be hot. Open the hood and remove the engine cover by pulling it straight up. It pops off with rubber ball/snap sockets. If you have a VW Passat, it's held with 3x 10mm nuts. You may be able to retrofit the snaps, see 1000q: snap cover retrofit for details.
If you have a Jetta, Golf, or VW New Beetle TDI, remove the intake hose right before the intake flap valve. (Does not apply to Passat). There are spring clips that hold the hose in place at each end. There may also be a T30 torx bolt or clips along the hose for the fuel line. Make sure the hose is free before removing it.
Remove the upper timing belt cover. It's held by 2 clips.
Loosen the 3x 13mm camshaft sprocket bolts shown below by a few turns. The bolts have oval holes on the sprocket which let the camshaft pulley (hub) rotate under the sprocket, within a range, without turning the timing belt. Do not remove the bolts all the way - just loosen them enough so that the pulley under the sprocket can rotate.
Ignore the black pin and ball in the picture below, it's from another writeup. The toothed window can help you determine how far you rotate the camshaft. Also note the oval bolt holes peeking out on the sides of the 3x 13mm bolt heads. If you can't see the toothed window, use the edges of the bolt heads as a reference to see how far you've moved the camshaft.
Do not loosen the larger center 18mm bolt. It holds the pulley underneath the sprocket to the camshaft. It'll probably be pretty tight as well.
Use a 18mm wrench on it and just gently tap on it to turn the camshaft a few degrees at a time. Too much and timing will move too far. Turning the bolt (and pulley underneath the toothed sprocket) clockwise will advance timing. Counter clockwise will retard timing. Again, you're not loosening the center 18mm bolt, you're just using it to turn the sprocket. The timing belt will not move, just the pulley and the camshaft.
If you want to use a sprocket counterhold tool like shown in the video below, the direction is the opposite. In other words, if you're moving the toothed sprocket, turning the sprocket counterclockwise will advance timing and clockwise will retard timing. The toothed sprocket rides on top of the pulley so turning one will move it in the opposite direction in relation to the other.
Tighten the 3x 13mm bolts to 18 ft-lb. You can choose to wait until after you're satisfied with the final position to replace the upper timing belt cover. However, make sure that nothing or no one can get caught in the timing belt. Objects falling into the timing belt can cause belt failure and serious engine damage. If it or any other belts catch loose hair/clothing/etc., or you, it can cause serious injury. Greatly overtightening the bolts can cause bolt failure and serious engine damage so make sure you use a torque wrench.
Replace any intake hosing that was removed. Make sure all tools are clear of the engine. Restart the engine and recheck camshaft torsion through VCDS.
When satisfied, replace the timing belt cover and engine cover. Double check that any intake hose tabs and quick connect clips are secured.
Here is a video that helps explain the procedure. In this example, timing needed to be advanced slightly after checking it to get to that 0.5 value but a tiny adjustment can result in a 2 degree change in timing.