1.9 litre 4-cylinder 90hp (A3 type) - used in various models sold until approximately 1998 in Europe and North America. Within this document we will call this the A3 engine even though it was also used in other models, because the most popular cars sold with this engine were the A3-chassis Golf, Jetta, and Vento sold from 1994 until early 1999. Not all model years were available in all markets, and this engine was replaced by the newer type (here called the A4 type) gradually over a period of years. Other models sold with this engine include the B4 Passat (1995 - 1997), VW Sharan minivan, and various Audi models.
The injection system uses a distributor-type pump. On cars with transverse engines, the A3 engine can be distinguished from the later type by the spin-on oil filter on the front of the engine facing down at an angle, the air filter housing is at the right front corner of the car, and the two black plastic pipes to the intercooler lead towards the left front corner of the car. There are other differences, but these are the most easily visible.
The turbocharger is a conventional wastegate type.
1.9 litre 4-cylinder 110hp (A3 type) - used on the same models as the 90hp but not available in all markets - in particular, not available in North America. Visually it is almost impossible to tell apart from the A3 90hp engine, except for the red "I" in the TDI badges used on the car in various places. The engine itself is identical to the 90hp model.
The turbocharger is a variable-vane type, and the injection system uses a distributor-type pump which looks the same as that of the 90hp model. Obviously there are differences in the ECU, and in the plumbing and controls for the turbo, since the turbo is not the same as for the 90hp model.
1.9 litre 4-cylinder 90hp (A4 type) - used in various models available in Europe and North America from 1998 on, this gradually replaced the previous engine as the car models were changed. Within this document we will call this the A4 engine because the most common application is the A4-chassis Golf, Jetta, Bora, New Beetle, and various models from Seat and Skoda using the same chassis.
The injection system uses a distributor-type pump. The oil filter is a cartridge type, and sits in a vertical container on the front of the engine towards the left of the car. On cars with transverse engines, the air filter housing is at the left side of the engine compartment and the two black plastic pipes to the intercooler lead towards the right front corner - exactly the opposite of the arrangement used on the previous model.
On North American models, the turbocharger is a variable-vane type. On European models, the turbocharger is a conventional wastegate type. The North American A4 engine is essentially a Euro 110hp A4 engine but with engine controls optimized for emissions rather than performance.
1.9 litre 4-cylinder 110hp (A4 type) - virtually identical in appearance and specification to the 90hp except for the engine controls; cars using this engine have a red "I" in the TDI badges. Not available in North America.
1.9 litre 4-cylinder 115hp "PD" - again similar to the A4-type engine but with the "pump-nozzle" injection system. Although the peak power is only slightly more than the 110, maximum torque is much higher and the engine has lower exhaust emissions. VW intends to gradually replace the 110hp models with this engine. Not available in North America, reportedly because the exhaust emission controls used on this engine cannot be used with fuels containing greater than 50 parts per million of sulfur, whereas at this writing (1999) fuels in North America can have as much as 500 parts per million.
Models with this engine have badges with a silver "T" and red "DI".
The injection system is the "pump-nozzle" type, and the turbocharger is a variable-vane type. The lack of the injection pump mounted on the front of the engine is the obvious visual difference.
1.9 litre 4-cylinder 150hp "PD" - Few details are available at this writing. Models with this engine apparently will have badges with "TDI" in all red.