TDI nozzle upgrade and fuel injector FAQ
VW and Audi TDI nozzle FAQ and selection guide
Also see: 1000q: nozzle installation detailed procedure
As a wear item, the fuel injector tips (the nozzle) should be regularly replaced. The TDI nozzles could last anywhere from 50,000-200,000 miles and beyond with normal use. However, the nozzle and its spray pattern gradually diminish. Replacement will restore it to like new condition. Worn nozzles won't cause any damage but replacing them will restore lost fuel economy, power, make less smoke, and give the car a smoother idle. This is because a worn nozzle's spray pattern is irregular and prevents optimum fuel combustion. Worn nozzles can also cause a bit of excess smoke on cold engine startup.
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.
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 car computer (ECU or ECM) does not know the size of the nozzle. When requested, a larger nozzle opening can inject slightly more fuel in a shorter time. Unlike a gasoline car which has O2 sensors to help sense fueling levels, VW and Audi 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 an effect on the amount of fuel injected). There is a sensor on the #3 injector called a needle lift sensor which sees the timing of the injection. Below is a picture of a mk3 TDI nozzle and injector partially disassembled. Pumpe duse solenoid injectors (~2004-2007) 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 1000q: direct injection vs. pumpe duse vs. common rail 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. Larger nozzles and a chip are considered a necessary supporting modification when adding a larger turbo. See 1000q: TDI turbo upgrade chart to see what options there are for TDI turbos.
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.
If you wish to have the nozzles calibrated and tested, kermatdi does this service. They will also do an injector "hot swap" with a deposit so there is no downtime shipping your injectors to them. (injectors cannot be damaged like from wrench marks or veg oil)
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. For best results, a good chipmaker will also fine tune fueling for your chip if you have larger nozzles, so it's up to you if you want chip, nozzles, or both, and in what order. See 1000q: basic performance upgrades and 1000q: advanced performance upgrades for more details on other options for increasing power.
Lastly, I do not recommend buying "e bay" or generic nozzles. TDI nozzles are not a common item so there aren't many brands to choose from. The brand name 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 much better than your old nozzles. While power may go up, it's sometimes accompanied by an increase in smoke (wasted fuel and unnecessarily high EGT). 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 their North American distributor kermaTDI.com. 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 with no further adjustments. I avoid parts sold by because this seller sells mostly copycat parts and because the seller 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, loss of potential power, excessive exhaust gas temperatures). My guess is that this is due to poor spray pattern and cheap construction / quality control.
Detailed nozzle size technical information
The below OEM nozzle size information is specific to VW and Audi TDI diesels with stock injectors. 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 and some newer aftermarket nozzles have 7 holes for a finer spray.
Note about aftermarket injectors: sizes should be close to advertised. For example, aftermarket .184 nozzles should be .184 Âµm (micrometers) and not .170 Âµm. Some ".184" stock nozzles were actually .170 Âµm. Aftermarket part numbers are highlighted in purple and follow the stock part number.
The newest generation of aftermarket nozzles use a diamond like coating (DLC) for better wear and spray characteristics, especially with ULSD (ultra low sulfur diesel).
.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), found on the 110 hp Euro AFN/ASV engine, actual measured size is .205 Âµm. 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 were discontinued (replaced with DLC520) and gave around +10hp, +25ft-lbs over stock nozzles. The new Bosio DLC520 feature the diamond like coating and give around +20hp, +40 torque.
.216 injectors: These will give more power than .205 injectors. There were also two different actual sizes for injectors commonly referred to as ".216". See below for more details on actual sizes. You need adjustment of the fueling to control smoke and when used with a chip, advanced modifications and a new clutch are possible requirements to be able to burn all the fuel with little smoke. They are not recommended for automatic transmission cars due to smoke.
The latest .216 nozzles are the Bosio DLC 1019 nozzles. These are 5 hole stock replacements for 150hp AXG engines.
Earlier 140hp 5 cylinder VW/Audi AEL engine "DSLA 150 P502" are true .216 µm 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.
.226 injectors: .226 µm orifice: Bosio DLC764 nozzles These are for cars with moderate turbo upgrades. The Bosio PPDLC764 stage 2 has a 7 hole tip instead of 5 hole and
DLC Race520 and Race520 stage2: These are for highly modified cars around the 200hp+ level. The stage2 has a 7 hole tip instead of 5 hole tip.
All pumpe duse injectors (all North American 2004-2006 VW diesels): the replacement is harder than earlier cars because you have to remove the valve cover and send the injectors to a specialized facility. This requires either car downtime or a core charge to hot swap injectors. If you still want injectors, kermatdi at http://www.kermatdi.com/ sells larger or modified pumpe duse injectors.
If you have a pumpe duse, I would recommend getting a chip first because you can always have the chip rewritten for larger injectors later. The average chip on a PD will make about 140hp/240 ft-lbs torque. Another issue is that you have to have the entire injector body modified at . 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 1000q: model year differences - pumpe duse.
The currently available PD injectors are:
Bosio DLC800: small power upgrade and mpg improvments, supports 100-170 hp.
Bosio DLC1043: moderate power upgrade, supports 130-210 hp
Bosio DLC800: for modified cars: supports 100-170+ hp
All common rail injectors (all 2009+ VW TDI): These are new engines and there are currently no aftermarket piezoelectric or solenoid injectors for this engine in the US. They use 8 hole common rail injectors. The CBEA/CJAA use piezoelectric and the Passat and mk7 cars used solenoid injectors.
Nozzle size recommendations
A common question is: if a diesel engine's rpm and power are regulated by fueling and not a throttle (see 1000q: how a diesel works), how do larger nozzles increase power? Larger nozzles give a tiny bit more fueling and make more power with a shorter injector duration, everything else being equal. But when you press on the accelerator pedal to request more maximum power, the larger nozzles have the capacity to flow more fuel. In a diesel engine, more fuel = more power.
A smaller nozzle should give slightly less fueling and make less power with a longer duration. Try to think of the injection pump as a pressure wave generator instead of a water pump. Fuel metering is regulated at the injection pump by the ECU/ECM. Larger nozzles can inject the requested amount of fuel in a shorter time and closer to TDC which can reduces smoke, effectively advances timing, and lowers EGTs. When you request more power, the injection pump can allow more fuel to be injected rather than just go back through the return lines. The disadvantage of larger nozzles is that they may not atomize fuel as well as smaller nozzles which can increases smoke. The latest 7 hole nozzles solve this by using more holes (7 vs 5) with smaller orifice size. Most people report a slight increase in smoke at heavy acceleration but unchanged or actually improved fuel economy with larger nozzles! This difference could be also be due to replacement of worn nozzles.
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. The latest DLC nozzles from Bosio use a diamond like coating to give greater service life with better tolerances with the decreased lubricity of ultra low sulfur diesel (ULSD).
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. In other words, assume that +2 size or larger nozzles could cause clutch slip.
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 the fueling.
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 the advanced performance modification FAQ article 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. The PP nozzles are being phased out in favor of the DLC nozzles. 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 VCDS to adjust fueling/smoke/economy to your personal preferences. You should not need a new clutch but it's a 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 5-15hp, +10-30ft-lbs torque.
.216mm nozzles will also work but will require recalibration of the fueling through VCDS 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. Most mk3 cars don't get clutch slip but some do. Mk4 and newer cars are slightly more likely to get clutch slip depending on what clutch you have.
.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 real 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. Mk3 passat and jetta which use the 1Z engine have slightly different pistons and rings, which also creates slightly higher smoke levels. 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.
Highly modified cars: Consult your chip tuner. The PPDLC stage2 (7 hole), DLC Race520 and DLC Race 520 stage 2 (7 hole) are only for highly tuned cars with at least moderate turbo upgrades and supporting mods.
Injector body technical details, pop testing
This section describes 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. Common rail fuel injectors are also very different (2009 and newer). 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 a wave of pressure inside of the injector body and fuel line, 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 to the top of the page, here is the link again: older VW injector being pop tested.
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
The #3 injector's needle lift sensor is a magnetic field sensor that detects the start, lift, and ending of the injection events. The pilot injection is how the ECU (car's computer) determines the start of injection. The fueling maps are based off calculated values and sensor readings including the needle lift sensor and crank sensor. If the needle lift sensor or wiring fails, the ECU falls back to a safety map.
The needle lift sensor detects movement (given as voltage) through the pressure pin (shown right) moving through a magnetic field. The ECU calculates the actual point of injection from this sensor and the TDC signal from the engine speed sender.
Shimming the injectors to adjust the pop pressure changes the timing. Remember, there are 2 sets of springs, pilot and main.
As fuel pressure builds up inside the injector, the pilot spring opens. A weaker 190 bar pilot spring advances the pilot injection because it opens sooner but effectively retards the relative main injection. A stronger 220 bar pilot spring setting retards the pilot injection because it opens later but advances the relative main injection.
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 VCDS.
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. The computer doesn't know the size of the nozzle but it does know how much fuel was metered at the injection pump and the duration and timing of the pilot injection opening through sensors (and not the nozzle).
Please refer to 1000q: injection quantity adjustment and the section "Testing and changing IQ with software adaptation" for details and screenshots. A summary of the procedure is below.
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.
Drive the car and let it warm up to normal operating temperature. While idling, open VCDS, login with code "12233", adaptation, block 1. Adjust adaptation value higher or lower to adjust IQ to the 3.0-5.0 mg/R range. Hit "save" when you are satisfied. When you are done, exit and then go back to make sure the values you wanted are still there.