TDI FAQ

Common questions and answers before proceeding further -

Q. Is it going to affect my warranty?

A. ANY modification that you make to the engine or its control systems could provide grounds for a manufacturer or aftermarket warranty supplier to deny a warranty claim.

Q. Is my engine going to blow up?

A. Whatever modification you choose, if it is done in moderation and properly set up, the likelihood of serious problems is very low (but not zero). In the later parts of this section that discuss individual modifications, wherever possible, we have provided some information to get you started on proper set-up of whatever it is that you are doing.

Q. Is it going to use more fuel?

A. Typically, properly-done modifications to a diesel engine DO NOT significantly increase fuel consumption unless the "extra" power is being requested all the time ... normally not possible in North American driving conditions. It should remain within a few percent one way or the other. The reason is that under part-load conditions that account for the vast majority of normal operation, most properly-done modifications do not significantly change the way the engine operates.

Q. Can I get <generally some ridiculously large number> HP from this engine?

A. The standard response for anyone involved in motor racing is this: "Speed costs money. How much do you have?" And it's not a linear relationship, either ... more like exponential. Keep in mind the limiting factors discussed in an earlier section. READ IT AGAIN. A conservative approach to engine tuning, using proven methods and components, will create little or no side effects if done properly. A more aggressive approach requires a certain amount of re-engineering of the vehicle and perhaps accepting some loss in long-term durability. Before setting a lofty horsepower goal, ask some questions. What are you going to be using the vehicle for? What are the essential minimum requirements for it to fulfill that role? What potential benefit is there to going well beyond those requirements and can the resulting expense and potential loss of durability be accepted?

It doesn't take 180 horsepower to cruise at 100 km/h ... or even 180 km/h. A bone stock 90hp engine will do that without any worries. It doesn't take 180 horsepower to do zero to 100 km/h in 8 seconds, either. So set realistic goals. Don't just pick a horsepower number for the sake of having it. For a daily driver vehicle, the overall results of a reasonable and conservative approach will be more satisfactory and less costly to achieve.

Q. Do I need to change how I maintain the vehicle?

A. All of the big power adders (chip, box, injectors) add more fuel, and if you use the extra power frequently, there will be an increased amount of soot added to the engine oil. It is advisable to shorten the oil change interval in these situations, and due to the potential for more stress and more heat loading, don't even think about using anything other than synthetic oil of the proper viscosity grade and specification approvals for your vehicle. It's also advisable to keep the air intake system in optimum operating condition, considering all components including air intake screen (if present - consider removing it), air filter, intercooler, and intake manifold.

Q. Is it going to increase exhaust emissions? Will I fail my annual inspection?

A. It may or may not affect exhaust emissions, but if properly set up, it is unlikely that the result will be a failed annual inspection. In most locations in North America, light duty diesel vehicles are either not subject to periodic emissions inspection at all, or are only subject to an exhaust opacity ("blackness") test. There may be a visual check that emission control components are in place and appear to be functioning. It takes a very poorly-running TDI engine to fail an exhaust opacity test, regardless of modifications (but see next paragraph). The possible need to pass a visual inspection should be considered before making modifications that are highly visible under the hood, and the procedures used for your local inspection should be considered prior to committing to a large expenditure.

Exhaust opacity tests at idle (most locations), or 2500 rpm no load, or at any constant cruising speed, are easy to pass. If your local jurisdiction does a dynamometer test at full load (most don't) that's a bit tougher, but even so, if your vehicle is properly set up it's not normally a problem. In the sections below, we have attempted to warn about configurations that might be prone to excessive exhaust smoke under load.

Q. The text in this document says I have to make other changes along with what I want to do. Do I REALLY have to do all that? Why can't I simply do what I want to do and nothing else?

A. In cases where other changes are recommended, if language such as "It will be necessary to ..." is used, then typically those changes really are necessary in order to prevent a bad side-effect, or at least to reduce the magnitude of the bad side-effect. In most cases, these recommendations are made based upon experience. You may find that if you try to skip steps, sooner or later you'll find out why those other changes were recommended ... hopefully not in the form of a shattered turbocharger or broken connecting-rod ...

Q. It says in this document that [some combination of modifications] is too much, or that [some setting] is too much. Why?

A. Typically - past experience, judgment, known limitations, known design documentation, calculations and extrapolations from similar but slightly different variations, and on and on ...

Q. Why not just import a European model that already has more power?

A1. For Canada - This CANNOT be done legally. You CANNOT register a vehicle in Canada which was not originally built to North American standards unless it is more than 15 years old. If the vehicle was not originally built to North American standards, Transport Canada WILL NOT allow the vehicle to be registered for the road. You CANNOT modify a vehicle to meet North American standards to satisfy Transport Canada - it has to be built to North American standards originally when it rolled down the original manufacturer's production line. And they don't make anything other than a 90hp TDI to North American standards (as of 2003 model year). Refer to www.riv.ca and link to the import regulations.

A2. For USA - There are authorized vehicle modification facilities that are capable of modifying certain vehicles (not all) to meet North American safety standards, but if it is fitted with an engine that hasn't got EPA's approval, that's going to be a big problem. For all reasonable and practical intents and purposes, it is impossible to import a vehicle into the USA and legally register it for the road if that vehicle was not originally built to North American standards by the original manufacturer (or it is more than 15 years old).

A3. General - Most vehicle registration systems are only concerned with the VIN (Vehicle Identification Number) - the chassis number. They typically don't pay attention to the engine number. There is a theoretical possibility that a drivetrain could be imported somehow (complete with ALL sensors, wiring, electronics, and accessories - typically these aren't the same as North American models) and put into a North American vehicle. No doubt this process isn't legal due to the use of an engine which has not gone through the EPA / Transport Canada approval process, but suppose somehow one finds a way around that. Now you have a vehicle in North America that has parts on it - including some scheduled maintenance parts, like the timing belt - that cannot be obtained through normal channels. You've now spent loads of money, and nobody will know how to fix it, and nobody will be able to get parts for it. And what happens a few years down the road when something better finally comes along? What little resale value is left owing to the difficulty of servicing goes right out the window. FORGET IT.

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Discussion of Popular Engine Modifications -

The following sections discuss popular modifications, starting with the modifications that are most common and WORK, and moving down to modifications that are less common and/or only helpful in conjunction with other alterations, and finally to some things that are either useless, or risky, or extremely expensive for what the benefit is, or require a high degree of skill and/or knowledge to do properly.
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The Chip (Chipping)

Popular manufacturers available in North America are Upsolute (www.upsolute.com) and Wetterauer (www.chip-tuning.com). Since all operating parameters of these engines are electronically controlled and their operation is governed by a memory chip in the engine ECU (electronic control unit), this modification consists of installing a different program on one or more "chips" contained within the engine ECU to alter the engine's operating parameters. Typically, these chips will slightly increase the maximum turbo boost pressure, considerably increase the maximum quantity of fuel delivered, and may slightly advance the start-of-injection timing under load, but with little or no effect on calibration at part-load conditions.

Installation: On A3 and B4 vehicles, the affected chips are "socketed" to the main board, so it is possible for an aftermarket chip to be purchased and installed by a moderately competent do-it-yourself mechanic following the manufacturer's instructions. On later models (New Beetle, '99.5-on New Golf and Jetta) the affected chips are soldered to the circuit board and can only be serviced using highly specialized tools, generally only by the vendor of the chip. It is recommended that this task be left to the vendor of the chip in question, in all cases.

Advantages: Easy, since you don't have to do it yourself. No home calibration or adjustment is necessary (although the fuel injection timing must be properly set to avoid excessive exhaust smoke). Suitable for someone who wants more power but knows very little technically about how the vehicle operates. Completely invisible to the eye, and to electronic scan tools unless the user of the scan tool knows specifically what to look for and is specifically testing for it. There is a large power gain, instantly noticeable when driving the vehicle. All vehicle diagnostic and sensor-checking functions remain intact.

Disadvantages: For later models, it is difficult (but possible) to reverse the modification should the need arise. For earlier models, reversing the modification is straightforward due to the socketed chips. It's hardly an issue ... you'll never want to go back to stock anyway. You are your own warranty.

Cost factor: US$300 - US$500 range

Cautions specific to this modification: Injecting more fuel using the stock injectors inherently extends the injection period later in the power stroke, so exhaust temperature will go up during prolonged operation at greater than the stock power output. Due to richer air/fuel and extended injection period, the tendency is towards more smoke in the exhaust, but normally the chip manufacturers stay within limits of exhaust smoke that are acceptable to most people and within limits of acceptable exhaust temperature. The vehicle will be more sensitive to fuel quality and proper setup of the injection timing for exhaust smoke. Set injection timing within specifications per shop manual but close to the "advanced" limit in order to ensure that the pump has enough capability to provide sufficient timing advance under load, otherwise exhaust will be smokier than necessary and the exhaust temperature will be higher than necessary. *DO NOT* use the "adaptation" settings in VAG-COM to provide more timing advance than the chip already specifies.

Suggested modifications in parallel: Turbo boost gauge; exhaust gas temperature gauge if vehicle is used for trailer towing or for prolonged operation near maximum speed and load; larger oil cooler. De-restricted intake and exhaust systems won't hurt.

"Bang for the Buck": If in doubt, DO IT!

What if I want more? A chip can be made to work with the next size bigger injectors, although it may take some effort (see later section). If any problems arise because of this, you are on your own to solve them. Clutch slippage, turbo damage, and high exhaust temperature are potential issues if modifications go far beyond that of a chip. Some people have run tuning boxes together with a chip, but this defeats the safety margins that the chip and box programmers have each individually built in, and there is a high probability that the maximum fuel delivery of the injector pump will be reached, causing all sorts of drivability and "check engine" problems. Dyno testing has found limited benefit from chip and box together ... typically there is more clutch-destroying torque, but little more peak power.

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Bigger Injectors

If you have a vehicle with a 90hp TDI and 5-speed manual transmission, you have injectors with 0.184mm orifices. If you have a 90hp TDI with automatic transmission in North America, you have injectors with 0.158mm orifices and a higher-pressure injector pump so as to push the same amount of fuel through these smaller injectors (for emissions reasons, at a cost of increased stress on the components and increased engine noise). The European 110hp model has what are known as 0.205mm injectors, and the European "Multivan" 150hp 5-cylinder TDI has what are known as 0.216mm injectors. All of these injectors are dimensionally interchangeable, so it is possible to install injectors one or even two sizes larger in place of the original ones. This will increase fuel delivery without the engine ECU knowing a thing about it, and it will do it without pushing the limits of the injector pump, nor will it extend the duration of the injection period - and not extending the duration is better for smoke, power, exhaust temperature, and efficiency.

Larger injectors are available in North America from www.dieselgeek.com (USA) or www.autobraun.com (Canada). Injector nozzel replacements are also available at places like www.kermatdi.com. Refer to the "Allowable combinations" table below before committing yourself to anything. You cannot order these parts from a North American VW dealer.

For the 90hp 4-cyl 5 speed injectors (known as 0.184 injectors) here are the part numbers you'll need (upgrade for automatics in North America only):
(Qty 3) - 028 130 202 P (there may be a suffix on the end indicating that it is reconditioned)
(Qty 1) - 028 130 202 Q (there may be a suffix on the end indicating that it is reconditioned)

For the 110hp 4-cyl injectors (known as 0.205 injectors) here are the part numbers you'll need:
(Qty 3) - 028 130 201 T (there may be a suffix on the end indicating that it is reconditioned)
(Qty 1) - 028 130 201 S (there may be a suffix on the end indicating that it is reconditioned)

For the 150hp 5-cyl T4 Multivan injectors (known as 0.216 injectors - biggest commercially available) here are the part numbers you'll need:
(Qty 3) - 074 130 201 K (possibly with a V on the end indicating reconditioned rather than new)
(Qty 1) - 074 130 202 R (possibly with V on the end)

Don't worry about reconditioned versus new. Reconditioned injectors contain all new working parts inside a re-used housing, and are quite a bit less expensive. Also don't worry about the opening pressure of the injectors, it affects the idle settings a bit but not much else.

Installation: This modification is not recommended for people who don't have good vehicle wrenching ability and troubleshooting skills. Professional installation might be possible, but if you're not comfortable doing this installation yourself, then you probably don't have the required skills and knowledge to troubleshoot and correct any problems or side-effects that may occur. The mechanical part of the installation is fairly straightforward, but you will need VAG-COM to recalibrate some functions in the ECU (easy if you have it ... www.ross-tech.com ), and some engine/injector/ECU combinations will require physical modifications to the turbo boost control system in order to get more air into the engine without blowing something to smithereens. To install the injectors, remove the clamps that tie pairs of injector lines together, loosen lines 1 and 4 at the pump end and remove them at the injector end. (Note the relatively low torque, not counting the initial "crack" to break the fitting loose.) Remove the clamps that hold injectors 1 and 4 down. Remove the drain-back hoses from injectors 1 and 4. Remove injectors 1 and 4 by applying a twisting action with a 15mm wrench while pulling up on the injector. Clean soot out of the seating surface in the hole in the cylinder head. Stick a new copper sealing washer to the new injectors with a dab of grease on the washer, slip them in, and torque the clamps to 20 lb.ft. Re-install all injector lines and tighten the lines at the pump. (Do not overtighten these fittings!) Start the engine (it will run on two cylinders at first) - run it for 5 seconds after the idle smooths out. Then repeat this process for injectors 2 and 3, remembering to deal with the electrical plug for #3, and transfer the drain-back fitting from the old #3 injector to the new one. Following completion of this, connect VAG-COM, and re-calibrate the EGR per section 7.j of this TDIFAQ, and re-calibrate the fuel delivery at idle to about 3 mg/stroke if you have a stock ECU and you only went up one injector size, or to the leanest possible setting (i.e. biggest reported number that can be achieved within specs) if you went up two injector sizes with a stock ECU or if you went up one injector size with a chipped ECU. On vehicles equipped with a VNT15 turbo, you should back off the initial response of the turbo to avoid dangerous operating conditions at low engine RPM and high engine load - see item 4b on boost control system modifications later in this document.

Advantages: Larger injectors are unique among the major power adders in that they inject a larger amount of fuel within the same amount of crankshaft rotation, and thus, for a given power delivery, they keep smoke and exhaust temperature to the minimum while also avoiding the increase in peak cylinder pressure caused by over-advanced start-of-injection timing. Given that the 110hp VW TDI engine is almost identical to the 90hp except for larger injectors, and that the 190hp "race TDI" developed by VW Motorsport uses even larger injectors but roughly the same injection timing and duration as stock, this method would appear to be the one favored by the engineers who develop the VW TDI. All injectors other than 0.216 look the same other than the part number, so the modification is invisible to the eye, and in the case of the 0.216 injectors, it takes a knowledgeable eye to spot a minor difference. This modification is transparent to electronic scan tools. Power gain will range from mild to wild depending on how big you go, but will be easily noticeable when driving the vehicle. All vehicle diagnostic and sensor-checking functions remain intact although the reported fuel delivery will no longer be accurate since the ECU has no way of knowing about the extra fuel being injected.

Disadvantages: Beyond the start we've given you in the "installation" section and the "Allowable Combinations" section below, you're on your own for ironing out any hiccups that may occur and not breaking something expensive in the process. You are your own warranty. You might need a different setting for reported fuel quantity at idle if you run into shudder problems (leaner - i.e. larger reported quantity - tends to reduce shuddering). Some ECU and chip and injector combinations may have shudder problems that cannot be resolved without going to a different chip, and not all combinations have been tested by someone. For example, the Upsolute chip for the '96 Passat "BK" ECU is not at all compatible with 0.216 injectors and (to my knowledge) has not been tested with 0.205 injectors, but the stock chip for the same ECU is OK with 0.216 injectors if AND ONLY IF reported idle fuel quantity is set at 6.4 mg/stroke. For the '97 Passat and Jetta, the Upsolute chip is compatible with the 0.205 injectors, although you'll need more boost pressure than the chip specifies. For the later models, no compatibility issues have been reported as far as drivability is concerned - but see the "Allowable combinations" table below.

Cost factor: US$550 - US$700 range, and you had better have VAG-COM ( www.ross-tech.com - about US$200).

Cautions specific to this modification: Since the ECU doesn't know about the extra fuel, it's up to you to either find settings that control exhaust smoke and exhaust gas temperature (if possible), or drive in a way that doesn't cause issues (not a good solution to require this to be done). READ THE "ALLOWABLE COMBINATIONS" SECTION CAREFULLY FOR YOUR PROPOSED SETUP. Most of that is based upon experience, and if you skip steps, sooner or later you're likely to find out why those other modifications are recommended. On A4-chassis 5-speed vehicles, going 2 injector sizes up with stock ECU or 1 size up with chipped ECU is likely to cause clutch slippage ... figure on an upgraded clutch. On automatic transmission vehicles, beware of exceeding the transmission torque limits, which are not known at this writing, but whoever finds out is in for an expensive lesson. On vehicles with VNT15 turbo and manual transmission, beware of high-load operation at low engine revs (see turbo discussion in "Limiting Factors" above, and item 4b - boost control system modifications - below).

Suggested modifications in parallel: Better clutch on A4-chassis manual transmission, if modifications more aggressive than 1 size bigger injectors with stock chip are done. Better final drive and differential (Quaiffe or Peloquin with bolted ring gear - only possible on manual transmission). Refer to the "Allowable Combinations" section below, for additional changes that may be necessary for specific installations. Refer to item 4b (boost control system modifications) as well. A larger oilcooler may also be a good idea

"Bang for the Buck": Pretty good, if you're capable of sorting out the ECU issues with VAG-COM and sensor tweaks, and you don't skip steps, and you don't try to do something that cannot be done. Lousy, if you bit off more than you can chew, or if you have no clue about sorting out those issues, and end up going back to stock or buying more parts in order to get a more conservative setup that's more suitable for normal use. The difficulty of sorting out these issues will depend on how wild you choose to go ... the wilder you go, the tougher the issues are going to be to deal with. See "Allowable combinations" discussion below.

What if I want more? Install a better intercooler and max out the fuel delivery, provided that your ECU will allow it without causing unacceptable shudder. Custom chip programming. Bigger turbo (which won't do anything without custom chip programming). Lower compression ratio (which you had better do if you go much beyond 18 psi boost pressure). Quaiffe or Peloquin final drive. Better bring lots of money ...

Allowable combinations of injectors and other modifications

This section is formatted as "If you are starting with ... then you can install ... provided that you also do ... subject to the following risks ...". See elsewhere in this FAQ for the "also recommended" modifications. ECU recalibration information is in the Maintenance Procedures section of this FAQ. Boost bleed for A3 and B4 vehicles is discussed in a later section (can't do it that way on an A4). Mechanical boost controllers are discussed in the Troubleshooting section of this FAQ under the topic "Fluctuation of boost pressure". It is highly recommended that a boost gauge be installed in the vehicle, for any situation where the corrective measures listed involve changing anything related to turbo boost control.

On A4-chassis vehicles, it is possible to fit an automatic's 11mm injector pump to a vehicle with a manual transmission. This document doesn't explicitly address this possibility, largely because it is an expensive modification and has only been done on a very small number of vehicles. If you propose to do this, then for purposes of interpreting the following data, pretend that fitting an 11mm pump in place of a 10mm pump is like installing injectors that are one size larger. (11mm pump with 0.184 injectors is like a 10mm pump with 0.205 injectors, etc.) If you have an A3 or B4 vehicle, the A4-chassis injector pump's wiring harness is not compatible, although we've heard that it is possible to make it work given enough effort. The 11mm pump is only available in A4-chassis form and can therefore only be fitted to an A3 or B4 with considerable difficulty due to the wiring differences.

Fuel system and engine control components from "pump-duese" engines are not at all compatible with the distributor-pump engines. This discussion pertains only to the 90hp distributor-pump engines as sold in North American specification through model year 2003. The 110hp distributor-pump engine already has 0.205 injectors as standard.

If you are starting with an A3 or B4 with stock chip and no tuning box, you can install 0.205 injectors provided that you recalibrate the EGR system so that maximum possible intake air is specified, and if you experience rough idling or shuddering at light load, recalibrate reported injection quantity at warm idle to around 3.0 mg/stroke. There shouldn't be any difficult issues to resolve. Power gains will be moderate ... probably a bit less than a chip with stock injectors, but this solution more closely resembles VW's official solution for the 110hp model (see "Advantages" above). Only install a tuning box if it is specifically suitable for use with this chip and injector combination.

If you are starting with an A3 or B4 with stock chip and no tuning box, you can install 0.216 injectors provided that you recalibrate the EGR system so that maximum possible intake air is specified, and recalibrate reported injection quantity at warm idle to around 5 to 7 mg/stroke (shuddering and drivability problems will probably be limiting factors - larger reported quantity helps both issues), and you install a bleed on the pressure sensing line that goes to the ECU so that the resistance upstream (to sensing line) and downstream (to atmosphere) of the ECU sensing port is about equal, and you install a mechanical boost controller in parallel with the standard N75 system calibrated to 17 psi maximum boost pressure which experience has been found is sufficient to adequately control exhaust smoke - fine-tune up or down if required, without exceeding 18 psi boost pressure. Tuning boxes will probably not work in this application - if you're having trouble controlling shuddering and/or exhaust smoke, adding more fuel is the last thing you want to do. There shouldn't be any issues beyond those discussed here. This configuration has been tested (author's vehicle), and has proven to work very well after the initial hiccups were ironed out, with acceleration tests showing power slightly greater than that of a chip with stock injectors in the same vehicle, *BUT* you need to be capable of dealing with the side effects!

If you are starting with an A3 or B4 with Upsolute or Wetterauer chip and no tuning box, you can install 0.205 injectors provided that you recalibrate the EGR system so that maximum possible intake air is specified, and recalibrate reported injection quantity at warm idle to around 5 to 7 mg/stroke (fine tune for shudder and/or exhaust smoke), and you install a bleed on the pressure sensing line that goes to the ECU so that the resistance upstream (to sensing line) and downstream (to atmosphere) of the ECU sensing port is about equal, and you install a mechanical boost controller in parallel with the standard N75 system calibrated to 18 psi maximum boost pressure which is the maximum allowable. You'll be fighting hard to control exhaust smoke with this configuration, and it may not be possible to completely solve the problem. A bigger intercooler, although costly, is really what is required. Although similar configurations have been tested on several vehicles, long term durability under high load conditions is not proven, since the power output will considerably exceed standard and is well beyond that of a chipped engine with stock injectors. Do not use any type of tuning box in this application - you've already got too much fuel. Clutch problems are likely ... see elsewhere in this TDIFAQ. Drag-racers should upgrade the final drive and differential. Remember, YOU ARE YOUR OWN WARRANTY.

If you are starting with an A3 or B4 with Upsolute or Wetterauer chip, don't even think about 0.216 injectors unless you're prepared for internal engine work to lower compression, a slightly larger turbo (but not too much!) such as a VNT17, custom intercooler, upgraded clutch, upgraded final drive, extra oil cooling, probably custom ECU programming to deal with all the issues that will occur. This will cost thousands of dollars to get right. Long term durability under high load conditions is not likely to be very good. We know of one engine with a similar configuration, having about 150hp to the wheels (roughly double the stock figure!), which suffered cracked pistons after about 80,000 km of admittedly hard driving.

If you are starting with an A4 5-speed manual with stock chip and no tuning box, you can install 0.205 injectors provided that you recalibrate the EGR system so that maximum possible intake air is specified, and if you experience rough idling or shuddering at light load, recalibrate reported injection quantity at warm idle to around 3.0 mg/stroke. There shouldn't be any difficult issues to resolve ... you're basically changing a 90hp into a 110hp. Power gains will be moderate, probably a bit less than using a chip ... but see "Advantages", above. Only install a tuning box if it is specifically intended for use with this chip and injector combination. Since you are your own warranty, it's worth checking whether you are getting boost pressure too close to the "surge" regime and making adjustments if required ... see separate section 4b below.

If you are starting with an A4 5-speed manual with stock chip and no tuning box, it seems likely that you can install 0.216 injectors provided that you recalibrate the EGR system so that maximum possible intake air is specified, and recalibrate reported injection quantity to a value that has yet to be determined but within the specification range of 2.2 to 9.0 mg/stroke (probably higher in the range) to control exhaust smoke. This combination hasn't been tested to this author's knowledge, but based on the A4's stock boost pressure being quite close to the final configuration of a B4 test vehicle with these injectors, it should work out with a bit of fine tuning. Exhaust smoke will likely be marginal at full load, though. It is strongly advised that the initial response of the turbocharger be de-tuned to avoid "surge" operation, per section 4b below, to preserve the turbocharger. Clutch problems are possible with this arrangement ... see elsewhere in this TDIFAQ. Tuning boxes will probably not work in this application - the smoke situation will be marginal, so adding more fuel won't help.

If you are starting with an A4 5-speed manual with Upsolute or Wetterauer chip and no tuning box, you can install 0.205 injectors provided that you recalibrate the EGR system so that maximum possible intake air is specified, and recalibrate reported injection quantity at warm idle to around 4 mg/stroke (fine tune for exhaust smoke), and make the turbo negative VNT adjustment indicated in section 4b below - DO NOT skip this step, it is vital to the life of your turbo. Although similar configurations have been tested on several vehicles, long term durability under high load conditions is not proven, since the power output will considerably exceed standard. Do not use any type of tuning box in this application - you've already got too much fuel. Clutch problems are almost a certainty ... see elsewhere in this TDIFAQ. Drag-racers should upgrade the final drive and differential. Remember, YOU ARE YOUR OWN WARRANTY.

If you are starting with an A4 5-speed manual with Upsolute or Wetterauer chip, don't even think about 0.216 injectors unless you're prepared for internal engine work to lower compression, a slightly larger turbo (but not too much!) such as a VNT17, custom intercooler, upgraded clutch, upgraded final drive, better oil cooling, custom ECU programming to deal with all the issues that will occur. This will cost thousands of dollars to get right. Long term durability under high load conditions is not likely to be very good.

If you are starting with an A4 automatic with stock chip and no tuning box, you can install 0.184 injectors provided that you recalibrate the EGR system so that maximum possible intake air is specified, and if you experience rough idling or shuddering at light load, recalibrate reported injection quantity at warm idle to around 3.0 mg/stroke. Only install a tuning box if it is specifically intended for use with this chip and injector combination. There shouldn't be any difficult issues to resolve.

If you are starting with an A4 automatic with stock chip and no tuning box, you should be able to install 0.205 injectors provided that you recalibrate the EGR system so that maximum possible intake air is specified, and recalibrate reported injection quantity at warm idle to around 3.0 mg/stroke, possibly a larger number if exhaust smoke proves to be an issue. This particular combination, at the time of this writing and to the knowledge of this author, has not been tested. Do not use any type of tuning box in this application, it will be marginal on exhaust smoke without adding still more fuel.

If you are starting with an A4 automatic with stock chip, don't even think about the 0.216 injectors, it will smoke too much.

If you are starting with an A4 automatic with Upsolute or Wetterauer chip and no tuning box, you can install 0.184 injectors provided that you recalibrate the EGR system so that maximum possible intake air is specified, and recalibrate reported injection quantity at warm idle to around 3.0 mg/stroke, or possibly slightly greater if exhaust smoke proves to be an issue. Do not use any type of tuning box in this application, it will be marginal on exhaust smoke without adding still more fuel. This configuration has been tested on quite a few vehicles with no known issues at this writing. Long term durability of the automatic transmission in this application is not known.

If you are starting with an A4 automatic with Upsolute or Wetterauer chip, don't even think about 0.205 or 0.216 injectors unless you have a transmission rebuild in the budget ... in addition to all the other things you'll need to control the exhaust smoke.

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4a. Boost Control System Modifications - A3 and B4 cars with GT15 or KO3 turbochargers -
This discussion must be separated into two parts due to the completely different operating characteristics of the wastegate-type turbochargers from the VNT-type turbochargers. This first subsection focuses on the wastegate-type turbochargers.

The purpose of these modifications on the wastegate-type turbochargers is to increase the steady-state boost pressure while greatly reducing the overshoots and fluctuations of boost pressure that are characteristic of the stock boost control system. This modification is only useful if other modifications (e.g. injectors) have been made that result in unacceptable exhaust smoke with the stock boost pressure. It is not to be done unless there is smoke from the exhaust and other causes of smoke (wrong injection timing, bad injectors, bad MAF sensor, EGR calibration problems) have been ruled out.

We can take no responsibility for what you do to your own car. Be aware that if you choose to do this, you are on your own. If you blow something up, you did it, not us. This modification can be made very cheaply but BE CAREFUL! It's very easy to blow something up by using too much boost pressure. Don't even think about messing with this unless you first install a boost gauge so you can watch what's happening. On the A3 models, the red hose in the engine compartment is boost pressure straight from the compressor discharge - easy to tap a pressure gauge into. To avoid false readings, the gauge connection should be made adjacent to the turbo or manifold before any signal-modifying bleed devices or mechanical boost controllers.

The boost pressure is controlled using a sensor which is inside the ECU. There is a small black hose which attaches to the intake manifold just where the intake manifold turns down towards the engine. (Make sure you're looking at the elbow that turns down towards the engine itself, not the one that turns down and goes into the turbocharger!) If you trick the engine computer into seeing less boost than there really is, then the engine computer will control it to a higher level. This is only useful if you have done other things that increase fuel delivery, and you need more air to control smoke and exhaust temperature as a result.

For a detailed discussion on this matter, follow this link:
http://forums.tdiclub.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=4&t=000529

It has been found advisable to use a mechanical boost controller in parallel with the stock boost control system if you do this. Refer to the Troubleshooting section of this FAQ, under the symptom "Fluctuation of boost pressure".

Do not operate the standard turbocharger at more than 18 psi boost pressure at sea level. (This must be de-rated in proportion to barometric pressure at higher altitudes.) Do not operate an engine with a stock compression ratio at higher than 18 psi boost pressure under any circumstances.

Installation: Straightforward for the knowledgeable do-it-yourself mechanic. Professional installation isn't really feasible, because most mechanics won't have a clue about how this is going to work and won't want to chance it.

Advantages: For vehicles that have higher fuel delivery than stock, this provides a method of controlling the smoke, and the mechanical boost controller provides control of the boost spikes and fluctuation that are characteristic of the stock boost control system.

Comments: Only worth doing on a highly tuned vehicle.

Disadvantages: A boost gauge is MANDATORY if modifications are done to the stock boost control system, and the driver is well advised to pay attention to that gauge, since these modifications remove the built-in safety features of the electronic control system. You are your own warranty. Remember ... no more than 18 psi boost pressure, under any circumstances!

Cost factor: Next to nothing for the bleed device, $35 for the mechanical controller from www.dawesdevices.com - and figure on another $100 or so for a boost gauge and a place to put it.

Cautions specific to this modification: YOU are responsible for making sure that you don't do something destructive to your vehicle.

Suggested modifications in parallel: This is only appropriate for a highly tuned vehicle with chip and injectors, that needs close to the limit of boost pressure (18 psi) in order to control exhaust smoke. A larger oilcooler may also be a good idea

"Bang for the Buck": Good.

What if I want more? Since this modification is only appropriate for a vehicle that already has more and is smoking badly as a result ... you already have more..
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4b. Boost Control System Modifications - A4 cars with VNT turbochargers
This discussion must be separated into two parts due to the completely different operating characteristics of the wastegate-type turbochargers from the VNT-type turbochargers. This second subsection focuses on the VNT-type turbochargers.
4b.1. Foreword and Disclaimer

This section discusses modifications intended to *prevent* turbo damage, so NOT doing anything about it may actually be the more dangerous scenario. Nevertheless, we can take no responsibility for what you do to your own car. Be aware that if you choose to do this, you are on your own. If you blow something up, you did it, not us. BE CAREFUL! It's very easy to blow something up by using too much boost pressure. Don't even think about messing with this unless you first install a boost gauge so you can watch what's happening.

The purpose of these modifications is NOT to increase the steady-state boost pressure (which is already higher than the older vehicles use, and very close to the safe upper limit if the vehicle is "chipped") but rather to control the fluctuations of boost pressure characteristic of the stock boost control system, and to REDUCE the amount of boost pressure at low engine speeds in the interest of preserving the turbocharger by avoiding operation in the "surge" regime. This will actually *reduce* responsiveness at low engine speeds, but it is a necessary step to preserve the life of the turbo, if other modifications which increase fuel delivery at low engine speed have been done. These modifications are only useful if other modifications (e.g. injectors) have been made that result in either unacceptable exhaust smoke or power fluctuation due to fluctuations in boost pressure that the stock boost pressure control system cannot control, or unacceptably high boost pressure at engine speed below 2000 rpm. The VNT turbo must not reach full boost pressure until above 2000 engine rpm, and should preferably produce no more than about 6 psi boost pressure at 1500 rpm, to avoid operating the compressor in the highly damaging "surge" regime. Turbo manufacturers recommend staying at least 10% clear of operation in the surge regime.

Since the A4 cars do not have any small-diameter hoses which carry boost pressure, it will be necessary to install a suitable fitting to access boost pressure. This fitting should preferably be located as close as possible to the turbo compressor outlet, such as on the lower intercooler pipe ... remove the pipe from the vehicle to install the fitting there. In order to facilitate future removal of this pipe for timing belt changes, use some sort of quick-connect detachable fitting to your new boost signal hose.
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4b.2. Test Procedure for Turbo Calibration - Low Speed Regime

If you have an automatic transmission, you don't need to worry about operating the turbo in the "surge" regime. At full engine load, the transmission will either downshift to a lower gear or unlock the torque converter, and in either case, the engine speed will be above the critical zone. Nevertheless, it may be worth performing a test similar to what is described below, and confirm that the transmission downshifts if floored at 2000 rpm in top gear before the boost pressure reaches 18 psi, and downshifts if floored at 1500 rpm in top gear before boost pressure reaches 6 psi in response to smooth application of pedal.

On manual transmission vehicles, to test whether you have a potential "compressor surge" issue, install a boost gauge, and then in 5th gear on level ground, preferably at an altitude of not more than 1000 metres, abruptly floor the accelerator at 1900 rpm and note the boost response. Ideally, it should smoothly rise to a peak which is not more than 18 psi somewhere near 2000 rpm. Try tramping the pedal to the floor at engine speeds between 1900 and 2100 rpm. It should never exceed 18 psi in this speed range. Not even for a split second. If it passes the tramp-the-pedal test, try accelerating through that speed range starting at slightly lower speeds and try it in different gears - confirm that initially after flooring the pedal, the boost pressure is lower than its eventual peak when below 2000 rpm, and that the peak is not reached until 2000 rpm. If it passes THAT test, reduce speed to 1500 rpm, and see if you can get more than 6 psi boost at 1500 rpm (don't floor it at this speed unless a few initial tests at part load suggest that you can floor it without exceeding that pressure). If it ever exceeds 6 psi at 1500 rpm or 18 psi at 2000 rpm, or if the peak boost pressure - whatever it is set to - is reached before 2000 rpm (never mind what happens at higher engine speeds), then you have a potential "compressor surge" issue, and you should consider performing the "negative VNT adjustment". Turbo manufacturers recommend staying 10% clear of the surge regime, and if you get it so that it passes these tests no matter what you try, you'll be around 10% clear of the surge line. (Don't be surprised if a bone-stock TDI fails this test procedure ... no chip no tuning box no injectors no nothing. Stock calibration is extremely close to the surge regime and normal production tolerances may put it into the surge regime.)
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4b.3. VNT Linkage Adjustment

To slow down the rate of boost pressure rise at low engine speeds, using a 10mm wrench and suitable hand tools, release the locknut of the VNT linkage (located above the diaphragm housing on the turbo) and adjust it 1 turn in the direction of lengthening the linkage, then re-tighten the locknut. YOU ARE NOW YOUR OWN TURBO WARRANTY. (If your vehicle was hot-rodded such that this modification was needed, you were already your own turbo warranty anyway, but hopefully the turbo is less likely to blow apart now.)

NEVER NEVER NEVER shorten the length of this linkage to less than it was stock. Attempting to increase the boost pressure at low engine speeds, or attempting to get the turbo to accelerate to full boost faster (which will cause a massive overshoot) is asking for a blown turbo. It has happened, so don't neglect this possibility!!
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4b.4. Test Procedure for Boost Control System Response

After performing the above procedures, to test whether you have a potential "spike" issue, in high gear at 2500 rpm, abruptly floor the accelerator and note the boost response. In the ideal world, it'll go smartly to the boost setpoint (which is not more than 18 psi) and stay there, but in reality with the stock boost control system, you'll get some overshoot. If it overshoots and fluctuates wildly before settling down, you need to do something to control boost spikes. If it survived this test at 2500 rpm, try it at 3000 rpm. Remember that 18 psi is the safe limit for continuous operation at sea level and this must be de-rated in proportion to barometric pressure at higher altitudes. If you're scared by what you see (and if you drive like that!), you need to do something to control boost spikes!

A mechanical boost controller in parallel with the stock boost control system can be installed as per the Troubleshooting section of this FAQ, under the symptom "Fluctuation of boost pressure". It is critical that any vent hole in this boost controller be soldered closed to prevent a vacuum leak, and this boost controller will ONLY work in parallel with the stock boost control system so as to eliminate spikes. It cannot be used to raise the boost pressure beyond standard. Do not operate the standard turbocharger at more than 18 psi boost pressure at sea level. Do not operate an engine with a stock compression ratio at higher than 18 psi boost pressure.

Installation: VNT adjustment is straightforward for the home mechanic but you're playing with something that costs several thousand dollars to replace - that's the scary part. Boost controller and boost gauge installation is more involved due to the need to partially disassemble things in order to install the fitting and gauge, and get the boost controller calibrated. Professional installation may be possible but ordinary garage mechanics probably won't want to touch it. If your vehicle has side curtain airbags and a "double DIN" radio, you're going to have a tough time finding a place for a permanent boost gauge.

Advantages: For vehicles that have higher fuel delivery than stock, this provides a method of controlling the boost spikes and fluctuation that are characteristic of the stock boost control system, in order to avoid potentially dangerous operation of the turbo in the "surge" regime, and in order to avoid potential overspeed of the turbo or engine damage due to overboost conditions.

Comments: A boost gauge is MANDATORY if modifications are done to the sto