Engine generations in Volkswagen TDI didn't change with body generations. This article shows the 3 types of diesel fuel injection used in TDI engines sold in North America: direct injection with a Bosch VE type pump, pumpe duse unit injector, and common rail diesel (CRD). Direct injection refers only to fuel that is directly injected into the cylinders instead of into a pre combustion chamber or intake manifold. While most TDI engines were 1.9 or 2.0 Liter, 4 cylinder, transverse inline, single turbo, and direct fuel injection, the method of direct injection is very different. (The 2004-2005 VW Passat TDI used a longitudinal 4 cylinder engine and the Touareg used a twin turbo V10 or single turbo V6). To keep it simple, this article focuses only on the basic differences in fuel injection. Cars outside of North America may have gotten some of these technologies before or after North America. See the FAQ button linked above to see a full list of DIY, "how to" specific to your car, and more general diesel FAQ.
These all direct injection and use a Bosch VE VP 37 type rotary electronic fuel injection pump. VE stands for verteilier, German for distributor. The rest is the model. The pump distributes fuel to the injectors using a rotary pump instead of an inline pump used on many diesels. The injection pump is driven by a sprocket off the timing belt. There were many models of Bosch injection pumps; TDI pumps are all electronically controlled and most will work on 1996-2003 TDI (some need slight modification for fitment). See 1000q: IP conversion for details on how to modify the ALH pump to fit on an older car.
TDI and this basic type of pump was first introduced in the 1989 Audi 100 5 cylinder 120hp TDI engine but North American didn't see it until 1996. The 1996-1997 Passat and some 1997 Jetta use the 1Z engine. The 1997-1999 Jetta use the AHU engine (same pistons and rods as the newer ALH engines). Since 1997 was a transition year for the TDI engine, most 97 should have 1Z but some might have AHU. These engines share the basic engine layout with earlier VW 4 cylinder engines. See 1000q: Mk3 jetta-passat interchangeable parts to see a more detailed list of shared parts between the Jetta/Passat. See 1000q: mk3 buying guide for a checklist when buying these cars.
In 1998 VW introduced the new ALH engine in the New Beetle (98-99 Jetta still used the AHU). For a number of reasons, manual transmission cars with the ALH engine are still the most fuel efficient TDI to date. 1998-99 New Beetle and all 1999.5-2003 New Beetle, Golf, and Jetta use the ALH engine. See 1000q: early mk4 buying checklist for a guide on what to look for on these cars.
These are all pumpe duse (PD), a new type of direct injection. It had been used in European TDI for a while before coming to North America. Check out the cosmetic differences between mk4 pumpe duse and non-pumpe duse Jetta to help identify what car you have (2004-2005 Passat TDI, BHW engine, and Touareg V10 TDI are all PD).
PD engines have significant mechanical differences from the earlier non-pumpe duse cars. 2004-2006 4th generation cars use the BEW engine (2004-2006 Golf/New Beetle) and 5th generation cars use the BRM engine (2005.5-2006 5th generation Jetta TDI). The difference is because the Jetta changed over to the 5th gen in 2005.5. All PD use a low pressure electric fuel pump (about 6-8 psi) in the fuel tank, something that earlier TDI did not. For a buying checklist for the early pumpe duse engines, see 1000q: pumpe duse engine checklist. For the A5 body pumpe duse, see 1000q: early A5 Jetta TDI buying checklist.
These use common rail CBEA or CJAA engines which also saw major changes. While the 2009-2010 Jetta sedan uses the same body as the 2005.5-2006 Jetta, it has a totally different engine/transmission and emissions control system. The 2010 VW Golf also uses this engine. For a buying guide for the 2010 Jetta TDI with review, MSRP, invoice price, options can be found in 1000q: 2010 Jetta buying guide and checklist.
The 2010 Audi A3 is the first TDI passenger car that Audi has sold in North America (they were sold in Europe for years). It uses the same common rail engine found in the newest Golf/Jetta TDI. To see more details on the 2010 Audi A3, see 1000q: Audi A3 TDI buying checklist.
also use common rail but in a very different layout. The VW Touareg TDI and Audi Q7 TDI SUV use the CATA V6 TDI longitudinal engine . If the Audi A4 is available with the TDI engine in 2011, the CATA TDI engine is the obvious choice. on that engine. While many of the basic principles of fuel injection apply to these larger V6 engines, the engine itself is very different. See 1000q: CATA engine FAQ to see details. The major difference to the end user is much more power, availability with AWD quattro, and that it must use urea solution injection into the exhaust to meet emissions standards (see the below videos).
Heated fuel filter - A common misunderstanding on all generations of TDI is that they had electrically heated fuel filters. No TDI was ever equipped with an electrically heated fuel filter from the factory. All but a few early 1998 TDI had fuel filters that were warmed a little bit by the return line fuel. When fuel returns from the engine it's warmed by radiant heat coming off the engine and from pressurization. When it's cold, the warmed return line fuel is recirculated through the fuel filter and back to the engine to help warm up and prevent fuel gelling. If the fuel gets too warm a thermostatic T bypass sends it back to the fuel tank.
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If your engine cover looks like one of these, this is what you have.
All North American VW TDI cars 2003 and earlier are not pumpe duse (pumpe duse was introduced years earlier in Europe). They use direct injection with the Bosch VE injection pump. There is no electric fuel pump anywhere on these cars. The fuel is drawn from the fuel tank under low pressure suction by the injection pump and pressurized by the injection pump to over 3300 psi at the injector. The injection pump acts more like a pressure wave generator than a simple water well type pump. Because of this, timing of the injection pump sprocket is very important. This is a common cause of timing belt job mistakes. See the full list of how to linked at the top to find the timing belt "how to" for your engine. The great pressure generated at the injector is created by restricting and focusing the wave down into a small tip, the injector nozzle.
Each fuel injector is a spring loaded, 2-stage, 5 port injector. All engines are water cooled, 4 cylinder, 8 valve inline engines. Here is a cutaway of a direct injection fuel injector. Please refer to 1000q: TDI nozzle and injector FAQ for detailed technical information and 1000q: nozzle replacement procedure if you want to remove the fuel injectors or replace the fuel injector tips, the nozzles.All cars are rated for about:
HP: 90 @ 4000rpm
Torque (ft lbs): 149 @ 1900rpm
HP: 90 @ 3750rpm
Torque (ft lbs): 155 @ 1900rpm
Cutaway of the fuel injector
Note the 2 stage injection - a pilot injection before the main injection softens the pressure waves of combustion and signal the start of injection to the needle lift sensor
The main injection occurs around 3190-3335 psi. The springs close the nozzle when the fuel pressure inside the injector drops.
Here is a video explaining the basics of how this type of hole injector
works. It's not specific to TDI but gives you an idea of the spring-fuel
pressure relationship. You can also see how there's some fuel that is not
injected and is carried away. This fuel helps cool the injector and nozzle
by carrying away heat.
Here is a picture of the cylinder head of a pre-pumpe duse car. It's immediately recognizable by the metal fuel lines from the fuel injectors to the diesel injection pump.
If your car is a 2004-2006 VW TDI and was sold in North America, it has a pumpe duse engine.
This includes all Jetta, New Beetle, Golf, Passat, and Touareg TDI. The
most noticeable change is the pumpe duse injectors and lack of a timing belt
driven Bosch VE fuel injection pump. If you have a mk4 Jetta/Golf/Beetle engine cover
that looks like the one below you have pumpe duse. 2004-2008 Jetta, Passat, and
Touareg TDI sold in North America were all pumpe duse.
Pumpe duse is VW and Audi's brand name for unit injector technology. Each injector is actually a miniature fuel pump - pumpe duse is roughly translated as pump nozzle. Unlike earlier TDI which had no electric fuel pump anywhere, pumpe duse cars use a low pressure (about 5-10psi) electric pump in the fuel tank, called a lift pump, to move fuel to the engine. Another low pressure fuel pump at the engine called the tandem pump (located at the end of the camshaft) moves the fuel into fuel rails where each fuel injector, actuated by the camshaft, pressurizes the fuel up to 27,846 psi where the release is carefully timed by a solenoid. The high stress on the camshaft and fuel injector is partly why VW recommends that pumpe duse cars use engine oil approved by VW for pumpe duse engines. Refer to: 1000q: pumpe duse engine oil for a list of some of the approved oils which are available in North America. Unlike earlier cars, both manual and auto transmissions cars use a fuel cooler in the front of the car due to the higher temperatures that the pumpe duse system puts into the return line fuel.
The camshaft has an additional four lobes over the older engines to actuate the pumpe duse injectors. Because these take up room, the camshaft valve lobes are narrower than in the past. Some have had excess wear. See 1000q: pumpe duse camshaft inspection for more details.
Aside from the fuel injection differences, the engine components are also different. Due to higher piston pressures, the pistons are heavier, have a smaller wrist pin, and do not have impressions for the valve heads like earlier pistons. They also feature slightly stronger connecting rods and bigger rod bearings. All engines are still water cooled and 4 inline cylinders, but the Volkswagen Passat engines are now slightly different than other TDI. The Passat engine is a 2.0L, 8 valve longitudinal engine and uses different components than the 1.9L 8 valve engines. Note: although sales brochures list the VW Passat as 16v, the 16v engine was never imported to the North American market. Many Passat TDI have had faulty chain drives and have had the oil pump assembly replaced with a gear driven assembly. See 1000q: Passat TDI oil pump chain FAQ for more details. There were 16v engines available in Europe.
Below left is a cutaway of a pumpe duse injector. Below right is a diagram of the injector in the cylinder head - the fuel rail is built into the cylinder head. Big changes vs. past injectors are in the valve spring like top which is actuated by the camshaft, the side feed fuel injectors, and the solenoid injection action.
Jetta, New Beetle, Golf: all use the 8v BEW or BRM engine
Passat: this used a 2.0L 8v BHW engine (sales brochures state 16v
but all Passat imported to North America were 8v)
VW had PD injectors that used a piezoelectric valve instead of an electric solenoid but these were never available on North American cars.
Here is a picture of the cylinder head on a pumpe duse car. You can see
the pumpe duse injectors in front of the camshaft. The Jetta also has
a different engine cover as shown above (see 1000q:
mk4 pumpe vs. non pumpe differences for more cosmetic differences). Here, there are only small metal fuel lines
parallel to the cylinder head.
Every 2009 or newer Volkswagen or Audi TDI sold in North America uses the common rail
engine. Here's an example of a Jetta engine cover.
Volkswagen switched to all common rail engines in 2009 for North American to meet emissions standards. Their marketing materials may state that they were meeting demands for quieter, more powerful engines but it came down to meeting emissions. The Jetta/Golf TDI use engine code CBEA or CJAA, a 4 cylinder transverse turbodiesel with 140hp, 236lb-ft torque. Although the engine code changed the engine is pretty much the same. The Touareg/Audi Q7 TDI use engine code CATA, a V6 longitudinal turbodiesel. This section focuses on the CBEA / CJAA engine - see 1000q: CATA FAQ for details on the V6 engine.
They use the same low pressure in tank electric fuel pump as the pumpe duse to pressurize fuel to about 5 psi from the fuel tank. It then goes to a medium pressure pump above the passenger side motor mount to be pressurized to about 73 psi. This is about what gasoline fuel tank pumps run at. It then goes to the high pressure fuel pump (HPFP)
The HPFP pressurizes diesel fuel up to 26,107 psi (1800 bar) in an "accumulator rail", shown below on a CBEA engine, a common tube/rail shared by all of the fuel injectors. Unlike most common rail systems which are made by suppliers, VW makes the common rail themselves. (Bosch makes the fuel pump). Fuel is metered at the pump but a fuel pressure regulator valve on the right end of the rail also controls fuel pressure in the rail by bleeding off pressure. Pressure is a byproduct of restriction so by closing the bleed valve, fuel entering the rail has nowhere to go and becomes pressurized.
For unknown reasons, there have been a more than a few reports of damaged
HPFP shedding metal flakes which cause severe damage to the fuel system.
Possible causes include faulty manufacturing, bad design, defective parts, contaminated diesel,
or gas in the diesel but at this point it's only total speculation. See 1000q:
fuel filter inspection for a basic check to see if there are flakes in the
A big advantage of modern common rail systems are their piezoelectric fuel injectors. They offer much better control over fuel injection quantity and duration then the older spring type fuel injectors or solenoid and camshaft drive pumpe duse injectors. Unlike older systems, they can inject fuel totally independent of cam timing. Piezoelectric injectors use a type of piezoelectric crystal that expands in response to electrical voltage instead of electromagnetic solenoids like pumpe duse injectors. The crystals can switch in a few thousands of a second, 4-5 times faster than a solenoid. The expansion of the crystal moves the nozzle needle. The needle can also be made with about 75% less mass. The effect of these faster, more precise injections is quieter, more powerful, and cleaner combustion. By injecting small quantities of fuel before the main injection, it smoothes out the pressure waves created by diesel combustion, thus quieting and smoothing out engine vibrations. Older injectors had only a pilot and main injection while piezoelectric fuel injectors can have up to 5 injections per stroke. This results in a smoother and quieter engine. The common rail injectors also feature 8 holes, which lets the same amount of fuel be injected in a finer mist, which also increases fuel economy and power.
Here is a video explaining the common rail system. It's for an Audi but the VW uses the exact same system.
Switching from 8 valve to 16 valve cylinder heads and better fuel atomization from common rail diesel injection (CRD) let the cars achieve a cleaner burn compared to earlier cars. New emissions treatments catch what is left over, making the car 50 state emissions legal. Smaller 4 cylinder Golf Jetta TDI use post injection combustion instead of adblue fluid for emissions treatments.
Mercedes Benz common rail engines have been using this technology for a while
but were not 50 US state legal due to emissions associated with their engine.
Generally speaking, the 6 cylinder common rail diesel engines sold in the US
like the BMW 335d, MB bluetecs, and VW/Audi TDI w/V6 engines use urea injection to meet
emissions. Part of the reason why the 4 cylinder VWs don't use urea injection because
the engines are smaller and don't have to burn more fuel to move larger, heavier cars. Here is a
video explaining the emissions treatments with Adblue urea injection on a
The "clean diesel" technology (similar to bluetec/bluemotion) in the Jetta and Golf use the fuel injectors to squirt a little bit of fuel after the main combustion to burn up trapped particulates in the exhaust system during an active regeneration self clean cycle. This regeneration occurs about every 400-700 miles depending on driving style, use, and how clogged the filter is. Some stuff gets burned off naturally during the passive regeneration which occurs during normal driving from exhaust heat. See 1000q: DPF and CRD emissions FAQ for more details on the system.
Another big engine change for the US is dual camshafts. The timing belt drives the exhaust cam and the intake cam is gear driven by the exhaust cam. The intake manifold is now in front of the engine instead behind and the exhaust manifold points up instead of down. The engine will also have pressure sensing glow plugs. The common rail engine uses a gear driven oil pump. The engine also uses a higher turbo boost than earlier engines. The CBEA engine uses about 22 psi of boost. Below is a picture of the common rail engine taken by gtidan and joetdi.
|Below: timing belt on the 4 cylinder common rail
engine. The exhaust cam is driven by the belt, intake cam is driven
by the cam gear.
Right: Another view of the timing belt system on a demo engine.
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