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TDI nozzle FAQ and selection guide and how to adjust injection quantity

Table of contents
Introduction (see below)

Introduction
As a wear item, the fuel injector tips (the nozzle) should be regularly replaced. The TDI nozzles can last anywhere from 50,000-200,000 miles and beyond with normal use. However, spray pattern and the nozzle gradually diminish, so replacement will restore the spray pattern to like new condition. If the problem is only related to minor buildup and not nozzle wear, run a can of diesel purge through the fuel system to help clean the nozzles. Worn nozzles will not cause any damage but replacing the nozzles will restore lost fuel economy, power, make less smoke, and give the car a smoother idle. This is because worn nozzles' spray pattern is irregular and disturbed, preventing optimum fuel combustion. I suggest PowerPlus Bosio nozzles because they have cone shaped openings instead of straight cylindrical openings, creating both more power and less smoke due to better fuel atomization. TDI nozzles are not a common item so there aren't many brands to choose from.
The needles and nozzle bodies are also matched to each other during machining. Nozzles with larger than stock openings will also make more power (and possibly more smoke) by injecting slightly more fuel, faster. This is because the TDI's car computer (ECU or ECM) does not know the size of the nozzle so a larger nozzle's opening can inject slightly more fuel in a shorter time. Unlike a gasoline car which has O2 sensors to help sense fueling levels, the diesels which use this type of injector have no sensor to determine fuel metering after leaving the fuel injection pump. (Fuel is metered at the injection pump but nozzles still have a small effect on the amount of fuel injected). There is a sensor on the #3 injector called a needle lift sensor but it only determines the timing of the pilot injection. Below is a picture of a VW TDI nozzle and injector. Pumpe duse solenoid injectors use some of the same concepts but this article does not focus on them. If you don't know if you have a pumpe duse, please refer to for more details.

If you use larger nozzles with a chip, it can create too much torque for the clutch and MAY result in clutch slip. Every car and every driver is slightly different so the recommendations here are on the conservative side. If you buy rebuilt injectors, the main component replaced is the nozzle so I suggest avoiding buying rebuilt injectors when a nozzle replacement is more economical and just as good.
If you demand the most precise fuel metering, have the injectors balanced and "pop tested". This requires specialized equipment and taking the injectors out to a specialized facility for the adjustment. It basically involves shimming the springs inside the injector so that all four injectors are balanced and delivering the same amount of fuel at the right pressure. To the right is a youtube video of an older VW injector being pop tested, the same principles apply. You could have them balanced immediately after installation but it doesn't give the nozzles a chance to break in, so 500 miles of wear is a conservative recommendation for the best balancing. In theory, nozzles are a precision machined item and should only wear in from new, but in practice, I prefer to let them break in. If you want the most balanced and most efficient injectors, have them cleaned and balanced every year but this is a bit much for all but the most demanding cars and is not economical for a passenger car. Also note that brand name nozzles tend to result in more consistent fuel metering even without injector balancing due to tighter tolerances and build quality. Because of this, most people will be fine without any pop testing as long as you replace the nozzles with quality units on an unmodified and working injector body. Of course, if you live near a facility which does pop testing or have another car to drive while your injectors are out, I recommend that you do have the injectors balanced and pop tested. Occasionally using diesel purge in the fuel system will also help keep it in peak condition.

An alternate basic power upgrade (instead of nozzles) would be a chip. A chip will give you more power than +1 size larger nozzles alone, but a chip is not a wear item. A good chipmaker will also adjust fueling for your chip if you have larger nozzles for the best results, so it's up to you if you want chip, nozzles, or both, and in what order. See for more details on other options for increasing power.
Lastly, I do not recommend buying "e bay" or generic nozzles. The only well known brand of nozzle for the VW TDI available in North America is the Fratelli Bosio brand. They are a well known Italian maker and sell the "Sprint" and "PowerPlus" nozzles, more information on the differences is below. Nozzles are subjected to extremely high pressures and require very fine machining. The consistency and quality is poor in generic nozzles and any money you spend on them may be wasted because they may not be better than your old nozzles. Generic nozzles could be great and they could be bad, but for such a small difference in price I would recommend buying brand name nozzles. Bosio nozzles are available through and . A factory defect or shipping damage is always possible but experience has shown these nozzles to be of high quality and result in better injector balancing when plug-play and no further adjustments. I avoid parts sold by because this seller sells mostly copycat parts and because they scammed me. The wholesale price of the copycat nozzles is about $5 and you get what you pay for. People who have tried them report that while they do increase power, they are also smoky (wasted fuel and potential power). My guess is that this is due to poor spray pattern and cheap construction / quality control.

Detailed nozzle size technical information
The below OEM and aftermarket nozzle size information is specific to VW diesels. Some of the nozzles below were measured with an electron scanning microscope by Geoff Williams "GeWilli", organized by smallest to largest. The "DSLA" means that the nozzle orifice is cut into the needle seating area. The "P" is the needle type that is in the nozzle- a 4mm diameter needle, and the "150" is the spray angle of the orifices. The last number is not the orifice size, it's just the name. Note that the nozzle orifices may be placed asymmetrically around the nozzle tip, some are, some aren't. The stock nozzles have 5 holes around the tip.
.158 injectors: DSLA 150P 672, OEM on the 90 hp auto transmission mk4 ALH 1998-2003 engine, actual measured size is .138mm.
.184 injectors: DSLA 150P 706 (some say France) OEM on the 90 hp manual transmission mk3 AHU/1Z (post smoke recall for the 1996 passat) 1996-1999 engine and the mk4 ALH 1998-2003 engine, actual measured size is .170mm. Remember that if you have this size nozzle and replace them with ".184" .170mm actual size nozzle you will see an increase in power because of the size difference.
.184 injectors: (Euro market: DSLA 150P 357)/(US market: DSLA 150P 442) (sprint 357/442 or PP357), OEM on the 90 hp manual transmission mk3 AHU/1Z 1996-1999 engine, actual measured size is .185mm. Similar to the "smaller".184 injectors used in later cars except it has a larger opening and was used in injector bodies with lower opening pressure (190 bar) used with different ecu programming pre-smoke recall in the 1996 passat. PP357 should give about +5hp, +10ft-lbs over comparable sprint nozzles with less smoke.
.205 injectors: DSLA 150P 520 (sprint 520 or PP520), found on the 110 hp Euro AFN/ASV engine, actual measured size is .205mm. These are the stock nozzles found on the 110hp Euro cars which also used a larger turbo and different ECU to account for more fuel. PP520 should give about +10hp, +25ft-lbs over stock nozzles and about +5hp, +10ft-lbs over comparable 520 sprint nozzles with less smoke.
.216 injectors: These will give more power than .205 injectors. Note that most people report better results from using later ".216" injectors instead of buying aftermarket .216 nozzles only due to better atomization of the fuel. There were also two different actual sizes for injectors commonly referred to as ".216". See below for more details on actual sizes. You definitely need adjustment of the fueling to control smoke and when used with a chip, advanced modification and a new clutch are probable requirements to be able to burn all the fuel. See for more details. They are not recommended for automatic transmission cars due to smoke.
Earlier 140hp 5 cylinder VW/Audi AEL engine "DSLA 150 P502" are true .216mm nozzles. Later 150hp Transporter (eurovan, not available in the US) 5 cylinder AXG engine "DSLA 150P 1019" are .203mm nozzles but seem to give better results due to differences in the injector body (nozzles are all interchangeable). The smaller nozzles used a longer duration to achieve the same amount of fuel but since your ecu doesn't know the difference, make sure you know what .216 nozzle you are getting. The actual .216 injector body looks slightly different than your stock smaller nozzle injector bodies but the nozzles are all removable and interchangeable. 150hp nozzles may also be called "DSLA 150P 764" and use .205 holes.
All pumpe duse injectors (all North American 2004-2006 VW diesels): the replacement is more complicated than earlier cars. If you have a pumpe duse, I would recommend getting a chip and seeing how the car feels at that power level. A chip alone will make about 150hp/250 ft-lbs torque which is quite a bit. Another issue is that you have to have the entire injector body modified at a specialized facility. This requires either car downtime or a core charge to swap someone else's injectors. If you still want injectors, kermatdi at sells larger or modified pumpe duse injectors. If you don't know if you have a pumpe duse, all North American VW diesels between 2004 and 2006 are pumpe duse. For more details, see .
All common rail injectors (all 2009+ VW TDI): This is a brand new engine and there are currently no aftermarket piezoelectric injectors for this engine in the US. Please refer to for more details. It uses 8 hole common rail injectors.

Nozzle size recommendations
General: Larger nozzles give a tiny bit more fueling and make more power with a shorter injector duration than a smaller nozzle, which gives slightly less fueling and make less power with a longer duration, everything else being equal. Fuel metering is regulated at the injection pump by the ECU/ECM. Larger nozzles inject the requested amount of fuel in a shorter window which reduces smoke, advances timing and lowers EGTs. The disadvantage of larger nozzles is that they may not atomize fuel as well as smaller nozzles which increases smoke. Most people report is a slight increase in smoke at heavy acceleration but unchanged or improved fuel economy with larger nozzles! Your old nozzles were probably worn out so new nozzles often result in more power, less smoke, and greater fuel economy than what you have now. So just read the recommendations below and see what you think. In general, the PowerPlus (PP) nozzles will give a slight increase in power and reduction in smoke over the OEM style sprint nozzles due to a ceramic coating, tighter tolerances on the nozzle, and a cone shaped orifice. The Sprint nozzles have a cylindrical orifice and are OEM style replacements but cost less and are still well made.
Also note that +2 size larger injectors OR injectors combined with a chip could cause clutch slip due to making more torque than the clutch can hold. Every car and every driver is slightly different, so just because someone else had no clutch slip doesn't mean you won't! Environmental conditions, car build variations, and the way that different chip tuners adjust their power delivery all affect the possibility of clutch slip. More torque may overcome the clamping force of the clutch and pressure plate (part of the clutch kit). The clutches used in 1996-2000 model year cars had higher torque ratings than 2000-2003 cars. The mk3 cars used a clutch that is similar to the vr6 (6 cylinder engine) clutch but had a different part number. The mk4 1998-2000 cars had a Luk clutch which had a higher torque rating than the 2000-2003 Sachs clutch, so early cars should be able to hold more torque than later cars. There may also be wear, driver, and other factors (like a tiny oil leak on the clutch) that will result in two otherwise identical cars with one car's clutch slipping and the other not slipping.
Perception and tolerance of smoke is also very subjective: just because someone said that "x" nozzle made no difference in smoke or "x" nozzle made no difference in power, your butt dyno and acceptable amount of smoke may be different! The engine condition, mileage, and calibration of two identical cars will always be slightly different, so what works on one car often turns out slightly differently on another car. The recommendations below are conservative guidelines. Also note that larger than stock nozzles may also cause a slight shudder at low load or slowdown or rough idling unless you adjust the fueling. The larger the nozzle the greater the chance for engine shuddering and the need for adjusting/leaning the fuel.
Automatic transmission mk4 ALH cars with and without a chip: There is no reason to replace these .158 size nozzles with identical nozzles. Sprint 357/442 and PP 357 all are .184mm nozzles and are recommended with a fueling adjustment since the higher pressure 11mm injection pump already supplies higher pressure fuel. Smoke is considered acceptable with the .184mm/auto transmission's higher pressure 11mm injection pump.
.205mm injectors with auto transmission cars will probably create more smoke than what most people like without more modifications, see for more details. It can work but the car will have at least some smoke so a conservative recommendation is to avoid this size with the automatic transmission without further modifications.
Manual transmission cars w/no fueling modifications/no chip: These cars use ".184" sized nozzles stock, but the actual size may have been .170mm or .184mm. The section above shows differences in stock nozzle sizes due to a slightly different injection pumps, etc. used in different cars. Sprint 357/442 and PP 357 all are verified .184mm size nozzles and are a good size for all manual transmission cars. The sprint nozzles are direct OEM replacements. The PowerPlus nozzles will give a slight increase in power and reduction in smoke. You should not need a new clutch if your only change is nozzles since this is about the stock power levels.
.205mm nozzles will also work and give a little more power/smoke than .184mm nozzles. You will have to adjust fueling with a VAG-COM to adjust fueling/smoke/economy to your personal preferences. You should not need a new clutch but it is a remote possibility with mk4 cars. It is very unlikely in mk3 cars. With no chip, this is probably the best choice for most people and will give a mild power increase of 5-10hp, +10-25ft-lbs torque.
.216mm nozzles will also work but will require recalibration of the fueling through VAG-COM or an injection pump adjustment to control smoke since the car will make some smoke. Clutch slip is unlikely with mk3 cars but possible with 2000+ mk4 cars.
Manual transmission cars w/a chip: Since .184mm nozzles are an OEM replacement, you should see a reduction in smoke and an increase in power with new nozzles if your old nozzles are worn. If you have an mk3 or mk4 car you should not expect clutch slip but it is possible from torque spikes from a chip alone, so don't blame it on the nozzles since they are just restoring your lost power/economy.
.205mm nozzles will require a fueling adjustment when combined with a chip. Try to get a replacement chip that takes into account the larger nozzles to minimize the chance for clutch slip and smoke. If you have an mk3 or 1998-1999 mk4, clutch slip is a possibility. If you have a 2000+ mk4 car, clutch slip with an OEM clutch is more likely with this size nozzle and chip. Mk4 cars will have slightly less smoke than mk3 cars due to the higher injection pump. Mk3 cars use a lower pressure 10mm injection pump and a conservative stance is that you will have a harder time controlling the smoke with a chip AND .205mm nozzles with no other performance modifications to increase the amount of air. Mk3 passat and jetta which use the 1Z engine have slightly different pistons and rings, which also contributes to smoke levels. See for more details. Again, acceptable smoke level varies by car and driver.
.216mm nozzles with a chip is too much fuel without additional supporting performance modifications. There will be smoke unless you have a larger turbo, intercooler, and a chip tuned for that size nozzle. A stock clutch will probably not hold up to these power levels so plan for a new clutch. See for more details.

Injector body technical details, pop testing
This section deals with describing the injector body, how it works, and how pop testing works for the 1996-2003 TDI. The pumpe duse (2004-2006) fuel injector is mechanically very different from earlier injectors and only a few of the same basic principles apply. When dealing with the Bosch VE injection pump system, think of the fuel coming from the pump less like water coming out of the faucet and more like a pressure wave.
Injector body details
The 1996-2003 TDI use a 2 stage spring fuel injector. The first stage is a pilot injection which serves to soften the pressure waves from combustion. The main injection is where most of the power comes from. As the pressurized fuel enters the injectors, it overcomes the weaker pilot spring which moves and triggers the pilot injection. As the injection pump builds up the pressure inside of the injector body, the stronger main spring then moves and triggers the main injection. See below for a cutaway diagram of the injector body.

Some 1996 injectors had the pilot injection begin at 190 bar and were replaced under a recall (with a new ecu) with 220 bar injectors which were used in all other 1997-2003 TDI. The pilot injection pressure is set by the pilot spring. This is part of the reason why the 1996 ".184" nozzles are the only actual .184mm measured nozzles and all later ".184" nozzles are actually .170mm. The .170 has a smaller orifice but a higher fuel pressure and different injection duration which means that the same amount of fuel is injected regardless of nozzle size.
The main injection in all injectors, both "190" and " 220" is set at 300 bar and is determined by the main spring.
Pop testing and shimming injector springs
Pop testing and injector balancing is a test where a specialized shop first cleans the nozzles and injectors to get a "clean" reading. They then measure and adjust the injector's internal springs so that all 4 injectors open at the same pressures. If they have to adjust the injector springs they do this by inserting shims (spacers) to adjust the preload on the springs inside. Most diesel injector shops can easily adjust the pilot injection but only a few can adjust both the pilot injection and main injection because VW uses a 2 stage injector instead of a 1 stage injector. Do NOT try this yourself, you need special hardened metal shims and pop testing equipment to do this.
The official VW tool is #1322. It builds up pressure inside of the injector body, simulating an injection pump, and lets you see on a gauge at what pressure the injectors "pop" their springs. Above was a youtube video of an older VW injector being pop tested, if you don't want to scroll up, here is the link again:
Although you can put in larger orifice nozzles as a plug - play modification, the best way to get them it all working as a system is to have the injectors cleaned, pop tested, and balanced by a professional who has equipment to adjust both stages of the VW injector.
Effect of injector shims on fuel injection timing

Also note that the pilot injection is where the ECU (car's computer) determines the start of injection. The #3 injector's needle lift sensor detects the pilot injection only, see below for a picture of the needle lift sensor. The fueling maps are based off the pilot injection, the car has no sensor to determine the main injection. If the needle lift sensor or wiring fails, the ECU falls back to a safety map.
The reason why the needle lift sensor can only detect the pilot injection is because the part of the sensor that detects movement, the pressure pin, is only actuated by the pilot injection.
Shimming the injectors to adjust the pop pressure changes the timing. The reason why is because as the fuel pressure builds up inside the injector, the pilot spring opens. A weaker 190 bar pilot spring will open earlier at 190 bar compared to 220 bar pilot spring injectors because there is less time between the pilot injection and main injection. The result is that ECU senses this and retards the injection timing. It will also smoke more. A stronger 220 bar pilot spring setting will smoke less and results in advancing the main injection. Again, the ECU only knows the timing of the pilot injection, and only off injector #3.

Adjusting fueling / injection quantity after installing nozzles
After installing new nozzles, you should notice a change in power, fuel economy, and smoke. If you installed larger nozzles and want to reduce smoke and fueling, you can fine tune the fueling with VAG-COM.
Fine tuning the injection quantity (IQ) tweaks the amount of fuel that is injected and can slightly adjust fuel economy and reduce smoke, everything else being equal. You may have noticed the section above where I wrote the computer "does not know the size of the nozzle". The computer does know how much fuel was metered from the injection pump and the duration and timing of the pilot injection opening through sensors (and not the nozzle). Larger nozzles let a bit more of the fuel that enters the injector body go into the engine within a shorter injection duration, one of the reasons why they can increase power and reduce smoke.
Procedure
First drive the car for about 500 miles or so to let the new nozzles settle in. If you also have a chip, you should ideally have a new chip made that takes into account the larger nozzles.
After getting the new chip and letting the new nozzles settle in, get a VCDS.
Drive the car and let it warm up to normal operating temperature. While idling, plug in the VCDS and start the software.
Enter "block 1 - engine". Login using the code "12233".
Go to "adaptation" and select block 1.
The default adaptation value, whether you have a chip or not, is 32768. The IQ value you see on the right is normally about "3.0-5.0 mg/R". A lower adaptation value entered in the blank will reduce fueling and increase the "x.x" m/R value. A higher adaptation value entered will increase fueling and lower the "x.x" mg/R value.
Hit "test" when you enter an adaptation value and see how the "x.x" mg/R value changes. There is a limit to how high or low you can change the adaptation value. Again, the higher adaptation value increases fueling and a lower adaptation value reduces fueling. A higher "x.x" mg/R value is less fueling, a lower "x.x" mg/R value is more fueling.
Hit "save" when you are satisfied. When you are done, go back and make sure the values you wanted are still there because a lot of people forget to hit save, which results in no IQ change.

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