PLEASE NOTE THAT THIS FAQ IS OUT OF DATE. Work is being done to move this to a wiki format with updated information, but please check out the TDIClub forums (http://forums.tdiclub.com) in the mean time for more updated information.
Disclaimer: While considerable effort has been made to make the information provided in this section as complete and accurate as possible, it does not and cannot cover all possible situations. The authors cannot accept any responsibility for any damages which may occur from the use or mis-use of these procedures, nor can the authors accept any responsibility for any damages which may result from personal injury or property damage which allegedly may be caused by the use or mis-use of these procedures. No responsibility is accepted for missing or incorrect information. Those who use these procedures shall accept all responsibility for performing the work which may be described below. If you have any comments or suggestions for additions or revisions, please contact the site administrator.
References within this document to "left" or "right" always refer to the orientation viewed from the driver's normal seating position. Throughout this document, you will see references to VAG-COM. Many diagnostic and calibration procedures cannot be performed without a VW specific diagnostic scan tool. VAG-COM is a reasonably priced software and cable that allow any Windows based computer to be used to communicate with the vehicle's on-board diagnostic system. Generic OBD-II code scanners (such as those which may be found at independent garages that do not specialize in VW/Audi) will normally NOT be sufficient - you need a VW specific scan tool. For more information about VAG-COM and to purchase a copy for yourself, see www.ross-tech.com - highly recommended.
This thread identifies VAG-COM users who may be willling to help: http://forums.tdiclub.com/showflat.php?Board=UBB17&Number=309894Here's a database of VAG-COM users in North America who might be able to help you: http://www20.brinkster.com/beowulf9/tdi/vagcom/Know which model you have. If you have a '96 or '97 Passat TDI in North America, you have a B4 chassis with what is known in this document as an A3-style engine, and you have a Garrett GT15 turbocharger. If you have a '97 through early '99 Jetta TDI in North America, you have an A3-style engine and you may have the Garrett GT15 turbocharger but more likely you have a KKK K03-006 turbocharger. If you have a New Beetle TDI, or a '99.5 or later Jetta or Golf TDI in North America, you have an A4-chassis vehicle, and you have a Garrett VNT-15 turbocharger.
The engine code number can be found on the build sheet which is typically near the spare tire on the floor of the trunk. In North America, engine code 1Z means 90hp A3-style engine with Garrett GT15 turbocharger and Pierburg MAF (mass air flow sensor). Engine code AHU means 90hp A3-style engine with KKK K03-006 turbocharger and Pierburg MAF. ALH means 90hp A4-style engine with Garrett VNT-15 turbocharger and Bosch MAF. European models don't necessarily correspond in specifications, engine codes, and model years (you're on your own, as far as figuring out what type of turbo and MAF sensor you have).
7) Maintenance
a. Engine Oil and Filter Maintenance
b. Fuel Filter / Water Separator Maintenance
c. Air Filter and "Snow Screen" Maintenance
d. Timing Belt Inspection and Replacement
e. "Supplementary injector" on 1996 Passat TDI models - North American specification only
f. Intercooler Cleaning
g. Intake Manifold and EGR Cleaning
h. Solving the "Slow-down Shudder" and Other Shudder Issues - Recalibrating the Fuel Quantity at Idle
i . Engine Power Supply Relay a.k.a. "Relay 109" Replacement
j .Avoiding the Need for Intake Manifold Cleaning - Recalibrating the EGR System
k. Setting the Injection Timing - Injector Pump Mechanical Adjustment
l. MAF sensor - checking and replacement
Based on the available information from oil analysis, an oil change interval under normal conditions of 16,000 km / 10,000 miles (or 1 year whichever comes first) is recommended when full-synthetic 5w30 or 5w40 oil meeting CG-4, CH-4, or CI-4 standards is used, as per the owner's manual. Note that owners manuals may not refer to the latest specifications for certain types of oils. Oil specification CI-4 supercedes CH-4, which already superceded CG-4 some time ago. Oils conforming to CH-4 or CI-4 (latest standards) may (and should!) be freely substituted for the owner's manual requirements for older specifications, without question.
If semi-synthetic, synthetic blend, or Group III oil is used which meets CG-4, CH-4, or CI-4 standards, an oil change interval under normal conditions of 12,000 km / 7,500 miles (or 6 months, whichever comes first) is recommended.
For conventional non-synthetic oil which meets CG-4, CH-4, or CI-4 standards, or for any oil meeting older standards such as CF, an oil change interval under normal conditions of 8,000 km / 5,000 miles (or 6 months, whichever comes first) is recommended. Castrol Syntec recommended by many dealers falls into this category, as it is a Group III oil meeting the CF standard. Mobil 1 also falls into this category as it meets only the CF standard, not CH-4.
ACEA B3 or B4 rated oils are also acceptable, at least for 2001 model year vehicles. In North America, the ACEA B3 and B4 rating is found on some *W-40 (and *W-50) oils that are not marketed as diesel engine oils (the latter would normally have the API CH-4 rating). They may be marketed as "oils for European engines" or some such.
API CF is not the same as API CF-4. Many more oils carry the API CF rating, compared to the number of oils that carry the API CF-4, CG-4, or CH-4 rating, but these are not suitable for TDI use unless they also carry another appropriate rating, such as ACEA B3 or B4.
If conventional oil of 15w40 viscosity is used, expected weather conditions also need to be taken into account, as the cold pumping ability of this oil is much less than that of the recommended 5w40 viscosity.
In the case of adverse driving conditions, such as trailer towing, mountain driving, driving under hot or dusty conditions, or driving consisting of mostly short trips, the oil change interval should be reduced.
Some forum members have installed oil bypass filtration units which continuously remove particles smaller than can be removed by conventional filters. Oil analysis indicates that these can safely extend oil change intervals far beyond what is conventional.
With the A3-type engine in a B4 Passat, removal of the lower engine pan is not necessary to change the oil. The drain plug is located at the rear of the oil pan, facing down at an angle, and is easy to reach. The oil filter is another matter, it's notoriously difficult on A3/B4 cars but it's possible to do from above. On a 1996 B4 Passat, there is a radiator hose blocking access, but this can be pulled out of the way without disconnecting it. A conventional strap-type oil filter wrench can be worked into position on the filter to remove it. Some oil spillage onto the lower engine pan is unavoidable. Before installing the new filter, pre-fill it with fresh oil, to minimize the amount of time that the engine runs without oil pressure. Then, the hard part is getting the new filter started on the mounting threads, because you can't see what you're doing, there's hardly room to feel your way, and you don't want to spill that brand new expensive synthetic oil now contained in the filter! With enough persistence, it can be done.
With the A4 models, the filter is a cartridge type, and is a snap to change, but the lower engine pan has to come off for access to the drain plug. You win some, you lose some!
Leaving the lower engine pan off, to facilitate oil
changes, isn't recommended. The lower pan performs several
functions. It isolates a certain amount of noise, it
keeps more heat within the engine compartment, it protects
many components from debris thrown up from the road.
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The change interval for the fuel filter is either 48,000 km / 30,000 miles, or 32,000 km / 20,000 miles, depending on model. Consult your owners manual for your specific vehicle.
The filter is a cylinder-shaped housing with hoses going into the top, easily visible at the extreme right of the engine compartment. It's possible to change the filter yourself. Make sure you have a supply of suitable clamps before you start the job, and also find some way to pre-fill the filter housing completely with diesel fuel before hooking everything up again, otherwise you'll have an awful time getting the engine to keep running until all the air is worked out of the system.
Back to Top7.b.1 Using pliers, pinch and slide hose clips away from filter (about 1 1/2in from hose ends) of fuel feed lines. Fuel feed is traceable back to a black line from the tank.
7.b.2 Use needlenose pliers and pull out (sideways, towards engine) return line clip for tee-piece. The tee-piece pulls straight up out of filter. The return line line is traceable back to a blue line from the tank. Wrap the tee-piece with a clean cloth or paper towell to protect from dirt.
7.b.3 Push (do not pull!) feed lines off the filter nipples (flat screwdriver blade helps). Wrap the ends with paper towells to protect from dirt. Use a Phillips screwdriver and release fuel filter clamp (vertical screw beside filter), holding filter from slipping down. Observe the positioning of the filter nipples.7.b.4 Gently lift filter straight up out of the car. Do not tip, as fuel may spill.
7.b.5 To drain the filter, on the bottom of the filter should be a knurled knob. Hold over a glass jar and unscrew (counter clockwise viewed from bottom) slowly. There is a nipple here where you can attach a short drain hose to avoid spilling. Try to contain drained fuel to a glass jar (old widemouth jam jar). This way you can see if there was water in filter. Drain about two ounces of fuel, and look for water droplets (may appear as beads, as water and diesel do not mix).Note that if you are draining and not replacing the filter, it is not necessary to disconnect the hoses; the filter can be unclamped and lifted up enough to access the knurled knob. THIS KNOB IS VERY FRAGILE. Don't break it off if you are going to be re-using the filter!Some analysis of the quantity of water in the filter is in order. It is determined by several factors, e.g. condensation in the tank, use of fuel treatments, and especially by your fuel supplier. If you buy fuel from the same place all the time, it may be usefull to check for water after say the first 5000kms as a safeguard to see what your supplier is giving you. If you see lots of water you may want to change to a different supplier. Stay well away from old barrels found lying in a field.
7.b.6 Set the old one aside and get the new one out now and install. Watch the orientation of the nipples. Tighten clamp you loosened in step 3 above.
7.b.7 Before you plug back on the return line tee-piece, it is wise to prime the filter with some CLEAN diesel fuel, and/or some straight fuel system cleaner. Failure to so do may result in a long cranking time before the engine starts, especially at lower temperatures.
7.b.8 Replace hoses, clamps and clip, then test engine.
7.b.9 Once engine is running, look at the "sight tube", i.e. clear line from filter to engine (if so equipped) - you may see air bubbles. They should almost dissappear, but there will still be a few after running for a while.Note: If you have a gross amount of air bubbles, there may be an air leak in the fuel supply side (or the tee-piece), and it may impact engine performance. Check hose fittings, connectors, especially the return line plastic Tee-fitting (has an O-ring) where it plugs on to the filter with the retaining spring clip.
In some areas, due to high levels of airborne contaminants, the "snow screen" will become clogged so quickly (resulting in power loss) that it becomes a considerable hassle. Many owners have removed these screens permanently with no ill effect other than slightly more frequent need to clean the main air filter element. The total frequency of maintenance may be considerably lower without the screen than with it in place ...
On A3/B4 models, the air filter housing is at the right front corner of the car. To access it, first remove the plastic cover between the top of the airbox and the headlight (it just pops out). Unplug the electrical connector at the airflow meter (between top of airbox and the large flexible hose). Pull the clear plastic fuel lines out of the clamp that holds them. Release the four clamps for the airbox cover and pull the airbox cover away to expose the filter element, which can then be removed for inspection. Unbolt and remove the screen which is bolted into the lower section of the air filter housing, and either clean it or don't bother re-installing it. This screen is very prone to clogging and some owners have found that it is better to leave the screen out and accept the (possibly) slightly greater frequency of servicing the main air filter. Re-assembly is the reverse, but don't forget to plug the airflow meter in again, and make sure the air filter element is properly seated in the housing at all edges and corners!
On A4 models, the air filter housing is on the left
side of the engine compartment. Release the clamps,
pull the cover off, and the filter element is right
there. Cleaning the screen requires removal of the lower
section of the airbox from the vehicle and then removal
of the duct which leads to the air filter housing intake.
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The timing belt should be inspected at every oil
change interval for evidence of any abnormal wear
conditions. This is easily done by unclipping and
removing the upper timing belt cover and performing
a visual inspection. If any of the following conditions
are noted, the belt and tensioner must be replaced
immediately without driving the vehicle any further:
- More than 1 or 2 mm gap between either edge of the
belt and the base of the flange on the front and rear
of the tensioner roller - indicating that the belt
is mis-tracking and is wearing at the edges.
- Excessive wear on any of the edges of the belt,
indicating mis-tracking.
- Evidence of cracks on the outer surface of the belt,
indicating that the rubber material is deteriorating.
- Evidence of oil, fuel, or other fluids on the belt.
These cause deterioration of the belt materials.
- Excessive wear on the teeth of the belt.
- If the belt has been on the vehicle for in excess
of the time or mileage specified in the owner's manual,
the belt and tensioner must be replaced with new components
regardless of the result of any visual inspection.
For A3 and B4 vehicles, instructions for performing a timing belt change can be found here: http://www.tdiclub.com/articles/A3-TimingBelt
For A4-chassis vehicles, instructions for performing
a timing belt change can be found here: http://www.tdiclub.com/articles/pdf/a4timingbelt.pdf
(PDF
version)
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Investigation by members of this forum have traced the problem to the "supplementary injector" which some models were equipped with. Under certain operating conditions, an injector located in the exhaust system sprays extra fuel into the exhaust to keep the catalyst warmed up. Although the official VW documentation insists that this system is only present and functional on models with automatic transmission (which were never actually produced), experience has shown that the system operates on the manual transmission models as well. This system proved to be extremely unreliable, and later models are not equipped with it. VW had great difficulty getting the early models to pass emission requirements, and hence the expensive replacement components listed above.
Fortunately for the backyard mechanic, the "supplementary exhaust injector" can be bypassed easily at negligible cost. To determine if your car has this system, locate the fuel filter on the right side of the engine compartment, and locate the two clear plastic hoses nearby. The smaller of the clear plastic hoses ends in a black "T", and one of those branches goes back to the top of the fuel filter and the other branch goes forward and down, to the exhaust injector solenoid mounted on the back of the airbox. The line coming out of this solenoid can be followed through a clip on the timing belt cover and then into a fitting on the exhaust downpipe.
To disable the "supplementary exhaust injector"
system, pull the hose which faces forward off the
"T" at the end of the smaller of the clear
plastic hoses. Plug the hose by jamming a wood screw
or some other suitable object into the hose, then
reconnect it to the "T" (to prevent a fuel
leak). No more "supplementary exhaust injector".
This modification will not cause a "check engine"
code to be set and there are no known adverse side
effects.
You will need a drain pan, a pail, some liquid dish detergent, and a fuel container with 2 litres of kerosene or other suitable solvent - don't use gasoline, or anything which will attack rubber. You will also need some vise-grips to hold the clamps open, and some channel-lock-type pliers for opening the clamps in the first place. Alternatively, buy some gear-type clamps that you can deal with a lot easier than the standard spring clamps, which are a hassle.
Locate the two black plastic pipes which go from the top of the engine down to the intercooler (which is at the left front on an A3, or the right front on an A4). Also locate the hose connection at the bottom of the intercooler and make sure you can get it open (just enough to drain fluid, you don't need to disconnect it completely) before starting.
At some suitable location, disconnect both pipes to the intercooler. Identify the pipe which goes straight down to the bottom of the intercooler. (On some models, the other pipe has some low spots in it which will trap liquids, you don't want to pour anything down that pipe.) Pour the kerosene into the intercooler and let it sit for a while. If possible, agitate the liquid once in a while by blowing into the pipe that goes to the bottom of the intercooler by some means. After 15 minutes or so, put the drain pan under the intercooler, and drain the liquid out. Chances are, it will be black! Don't pour this crap into your fuel tank, use it to fill your camp stove or something.
Now, close the bottom pipe, and squirt some dish detergent down into the intercooler. Measure out 2 litres of hot water, and pour that into the intercooler. Let that sit for a while, and agitate it by blowing into the pipe if possible. Then drain that out. Chances are, that will be murky, too!
Inspect the system for any low spots that would trap liquid, and get the liquid out of there by whatever means are needed, before you start the engine. Make ABSOLUTELY SURE there's no standing liquid anywhere inside, then reconnect everything.
You should be aware that the CCV (crankcase vent) system
is the reason for the gunk accumulating in the intercooler
in the first place. The CCV hose goes from the round
black housing on top of the valve cover and into the
air intake pipe. Pull that hose off the black CCV housing
and check for sticky black gunk inside. If you don't
want to have to clean the intercooler again, and if
it's legal where you live to not have a CCV system,
then you can connect a 3/4" PVC hose to the black
PCV housing and run the hose to somewhere (keep it away
from moving parts and from the exhaust system), and
plug the end of the hose that normally hooks up to the
PCV housing with a 3/4" pipe plug and a hose clamp.
In most areas, this setup is not legal for on-road use,
so you'll just have to periodically clean the intercooler
to maintain peak performance.
Here is another writeup on Intercooler Cleaning: http://www.tdiclub.com/articles/Intercooler_Cleaning/
But if you didn't do that, and your vehicle is suffering from lack of power at higher engine speeds at all times, you need to clean the intake manifold. The following procedure is generic to all TDI vehicles. Individual vehicles may differ slightly.
Don't even THINK about cleaning the intake manifold without removing it from the vehicle ... engines don't like breathing solid particles.
CAUTION: This is an involved procedure. None of the steps are particularly difficult but the procedure requires diligent attention to how everything is disassembled in order that reassembly proceeds smoothly. Read the entire procedure before deciding upon whether to attempt it yourself. If you are not comfortable with the procedure, then arrange for it to be done by someone qualified. Expect to pay for several hours of shop time in that case, because that's what will be required.
7.g.1 Remove the top engine cover. Since it may be necessary to access some bolts from underneath the vehicle, support the front of the vehicle securely on safety jack-stands and remove the lower engine cover.
7.g.2 Disconnect the small-diameter black vacuum hose from the silver EGR diaphragm.
7.g.3 On A3 and B4 vehicles, remove the screw that attaches the upper and lower intercooler pipes, unplug the temperature sensor located on the upper intercooler pipe, disconnect the small diameter hose from the upper intercooler pipe, unclamp both ends of both pipes and remove them from the vehicle.
7.g.4 On A4 vehicles, unclamp and disconnect the upper intercooler pipe from the intake manifold adjacent to the EGR diaphragm and valve, and remove the rubber elbow from the vehicle.
7.g.5 On A3 and B4 vehicles, remove the bolt that attaches the turbo intake pipe to the intake manifold. Release the hose clamp that attaches the turbo compressor outlet pipe to the turbo outlet, and pull the metal turbo compressor outlet pipe out of the vehicle. Cover the turbocharger so that no dirt can get into it.
7.g.6 On vehicles not equipped with an EGR gas cooler, unbolt the EGR transfer pipe at both ends (exhaust manifold and EGR valve), and remove it from the vehicle. On vehicles equipped with an EGR gas cooler, unbolt and remove the EGR pipe from the exhaust manifold to the cooler, then unbolt and remove the EGR pipe from cooler to EGR valve, then unbolt the EGR cooler from the back of the intake manifold. Some of these bolts may require access from underneath the vehicle. Then swing the EGR cooler out of the way. The coolant hoses may be left attached to the EGR gas cooler.
7.g.7 On A4 vehicles, disconnect the linkage at the anti-shudder valve and unbolt the solenoid and actuator assembly, and detach the EGR / antishudder housing from the intake manifold. It may prove easier to leave the solenoid and actuator devices connected to the vehicle but hanging loose. Remove the EGR / anti-shudder valve assembly from the vehicle.
7.g.8 Remove the 6 bolts which secure the intake manifold to the engine. It will be necessary to bend a heat shield on the exhaust manifold out of the way to remove the 2 right-most bolts; this can be done with carefully-placed hits with a hammer on a long screwdriver. On some models, it will be necessary to remove the oil feed line to the turbocharger in order to access one of the bolts. The fitting at the turbocharger will probably be seized and will let go with a sharp "crack" upon applying firm pressure. Use a wrench which fits well over the fitting so that it doesn't slip. Cover the oil feed to the turbo, and protect the oil pipe, so that no dirt can enter either component.
7.g.9 Remove the intake manifold from the vehicle after confirming that nothing else is in the way.
7.g.10 The intake manifold can be cleaned out by a number of methods. Paint remover, acetone, and other solvents can be used to soften the goop. (Do this away from anything that may be damaged by the nasty solvents and away from any ignition sources due to their flammable vapours!) A high-pressure washer is useful. Bead-blasting has also been used but make sure all the beads are out of there before re-installing the manifold on the engine.
7.g.11 Debris also accumulates in the inlet ports of the cylinder head, but these are very difficult to clean without getting too much debris into the engine. One method that has been suggested involves placing cotton balls just inside the ports, cutting a bevel in the crud so there is not such an abrupt transition, and sucking the balls and cut-off bits of crud out with a shop vacuum.
7.g.12 Assembly is generally the reverse of removal.
If you had to remove the turbo oil feed line, make sure
you reconnect it, and don't over-tighten the fitting
at the turbo. It will not be possible to get a torque
wrench on most fasteners, so use common sense when re-installing
the bolts. You don't need a new intake manifold gasket.
Note for '96 Passat and possibly other older ECU variations: The adaptation numbers are in a different range, and you won't be able to get feedback on what you are doing on the same screen. You'll have to flip between "measuring blocks" group 1 and "adaptation" block 1 to see what's going on.
Physical adjustment of the upper section of the pump is also possible to recalibrate the fuel quantity but it is strongly recommended that the adaptation method be used first. The physical adjustment method requires the use of a special tool to loosen the special security bolt on the injection pump, then the other 3 bolts that secure the top 2 sections of the pump to the housing (you can leave the upper cover in place - it's movement at the second split that you are after). In addition, this method still requires the use of VAG-COM to ensure that the injection quantity remains in the proper range. THIS METHOD IS NOT RECOMMENDED FOR BEGINNERS. It is a "last resort" to solve an engine that persists in not running correctly despite all other attempts, and which has had major surgery performed on the injector pump, and even then, ONLY if a VAG-COM check finds that the pump is out of OEM specifications (2.2 to 9.0 mg/stroke at warm idle in neutral with all accessories off). CAUTION: Improper physical adjustment of the pump is capable of causing an "engine run-away" condition which will result in severe engine damage. ALWAYS ensure that if a physical adjustment is done, that the adaptation setting for group 1 is at factory default and that after completion of all work, the reported quantity at idle is within factory specifications.
A VW specific scan tool such as VAG-COM is required for this procedure. With the engine warmed up and running at idle in neutral with all major accessories such as air conditioning turned off, connect the scan tool cable and start the scan tool software. Select engine control module. "Login" using 12233 as the access code. Select "adaptation" and go to adaptation block 3. Give the accelerator pedal a quick "blip" to ensure that the EGR remains turned on for the next minute while you perform the following steps. Note that the display shows a default adaptation value of 32768 and shows approximately 250 +/- 20 mg/stroke of air intake volume. (If it does not show this, you are either on the wrong screen, or you have an older ECU that differs slightly - see next paragraph.) If all is well, enter 33768 as the new adaptation value, and select "test". Note that the displayed air intake volume changes, usually to about 370 mg/stroke. The specification limit is 370 mg/stroke, so if you want to remain within OEM shop manual specifications for emission control reasons, you might have to enter a number slightly smaller than 33768. (If you don't care about road-legal NOx emission limits then leave it at 33768. [Depending on the usage cycle, NOx at this setting can be increased by as much as 40%]) If all is well and you have a seting that you are happy with which results in an intake air volume of 370 mg/stroke or just a hair less, enter "save". Now your intake manifold either will never clog, or will take so long that the engine will wear out first.
Note for '96 Passat and possibly other older ECU variations:
The adaptation numbers are in a different range, and
you won't be able to get feedback on what you are doing
on the same screen. The EGR adaptation number for a
'96 Passat with the original "BK" ECU is 188
rather than 33768 and you'll have to go back to "measuring
blocks" group 3 to see the effect before "saving"
the new setting.
As for warranty, no one has mentioned any problems nor should there be. This
adjustment is also completely reversable should one be concerned.
Most provinces and states that do emissions testing on diesels,
just check opacity, so this will not be a factor when testing.
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With the engine warmed up and idling, connect the diagnostic tool, and select the engine control module. At this point, one of two different procedures is necessary, depending upon whether you have the proper factory service manual for your particular vehicle.
If you have the factory service manual, select "Measuring Blocks", group 0, then select "Basic Settings". The glow plug indicator lamp will begin flashing at this time (this is normal). Do NOT forget to go into "Basic Settings" because this procedure is completely invalid if measurements are taken outside of "basic settings". Take note of the 2nd and 9th numbers in the display. Locate the chart in the factory service manual which shows the proper relationship between these two numbers. Go across the chart with the 9th number then up the chart with the 2nd number and make sure it is within the shaded area. It has been found through experience that these engines have better cold starting characteristics if the setting is within the upper half of the shaded area. If it is good ... don't do anything further. If the second number is below the recommended range, you need to make a mechanical "advance" adjustment (see below). If the second number is above the recommended range, you need to make a mechanical "retard" adjustment (see below).
If you don't have the factory service manual, select "Measuring Blocks", and go to group 4. Do NOT use "basic settings" for this method. The displays show the requested injection timing, the actual measured injection timing, and the duty cycle of the advance solenoid. At warm idle in neutral, requested timing should be between 0.4 and 2.0 degrees BTDC. If the actual timing is not more than roughly 3.0 degrees BTDC, and the duty cycle of the advance solenoid is not more than 10%, the timing is good ... don't do anything further. If actual timing is more than 3.0 degrees BTDC, you need to make a mechanical "retard" adjustment. If the duty cycle is more than 10%, you need to make a mechanical "advance" adjustment.
If you have an A3 or B4, you need to rotate the body of the injector pump "forward" to retard the timing and "backward" to advance the timing. Stop the engine. Remove the upper timing belt cover. Rotate the engine by hand (shifting trans into 5th gear and pushing the whole car works) such that the two nuts at the rear and bottom of the injector pump flange can be reached through the access holes in the pump pulley. Loosen these two nuts by 1 turn, loosen the bolt at the top front of this flange 1 turn (accessed from outside, not within the pulley). Loosen the bolt located at the opposite end of the pump below the four injector lines. With a 17mm wrench, loosen by 1/2 turn the injector lines on the end of the pump. Now you can rotate the entire pump housing in the required direction (make VERY SMALL adjustments) then tighten and reassemble everything and recheck the timing.
If you have an A4, you need to remove the upper timing belt cover and adjust the relationship between the inner and outer parts of the injector pump pulley. To advance the timing, the inner part of the pulley (together with the pump shaft) needs to move "forward" with respect to the outer part of the pulley. To retard the timing, the inner part needs to move "backward" with respect to the outer part. The 3 bolts which secure the two parts of the pulley together may or may not be "stretch bolts" that must be replaced every time you do this ... so it's a good idea to get 3 new bolts just to be sure. Make all the adjustments using the original bolts, then replace the old bolts with the new bolts and torque them one at a time.
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