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Friday, 15 May 2015

Common faults with VAG vehicles with tandem fuel and vacuum pumps

Common faults with VAG vehicles with tandem fuel and vacuum pumps in the Carworkshopblog
Main parts   
This post will investigate the two most common faults that occur in the VAG group's tandem pumps.

These types of pumps are installed in those engines equipped with the pump injection system.


The tandem pump unit is a set of two pumps in one unit with very differing functions.  The entire pump assembly is driven by the camshaft.

One of the functions of the assembly is the vacuum pump; which generates the vacuum for the brake servo. The second function of the assembly is a fuel pump which sucks fuel from the fuel filter to the feed pipe located in the cylinder head and supplies the injectors.
The working pressure of this pump varies between 8 and 12 bar depending on the model.

FAULTS
Common faults with VAG vehicles with tandem fuel and vacuum pumps in the Carworkshopblog
The most common faults in this type of pump are as follows:

Loss of fuel.

Mixing of oil with fuel.


PROCEDURE AND SOLUTION

The repair procedures for either of the two faults are practically the same except for the additional tasks required in the case of oil and fuel mixing, which are:

  • Fuel filter replacement
  • Checking the engine oil level

 In both cases the problem can usually but not always exclusively be located in one of the gaskets or on the pumps main shaft oil seal.




Juego de juntas de la bomba Tándem en motores del Grupo VAG
Set of gaskets   

1- Obtain a gasket set for the repair, as shown above
  
2- Remove the tandem pump in order to carry out the repair work. Take precautions to ensure fuel is not spilled on to the gearbox as it will contaminate the clutch disc causing it to slip and making it difficult to engage the gears.


Common faults with VAG vehicles with tandem fuel and vacuum pumps in the Carworkshopblog
Mesh before the return pipe     

3- Remove the cover where the fuel return valve is located (4 torx 20 bolts). 

  • Clean the inside of the housing.
  • Clean the mesh with compressed air, this mesh is not supplied in the replacement gasket kit.
  • Replace the gasket.
  • Refit the cover using new bolts.

4- Remove the black cover fastened with 5 torx 30 bolts.

Remove the rotor cover fastened with 3 torx 20 bolts (see the picture below)
Replace the rotor pressure springs (see the image below)
Ensure the cleanliness of the housing and repair procedure.
Replace the gasket
Fit both covers in reverse order (replace the 5 black cover bolts)

Vista interna de la bomba Tándem en motores del Grupo VAG
Left photo: Rotor cover bolts - Right Photo: Pump rotor and pressure spring

5- Remove the three torx 30 bolts that appear in the following picture:


Vista interna de la bomba Tándem en motores del Grupo VAG
Bolts for the tandem pump body

  • Remove the body of the pump from its base on the cylinder head.
  • The pumps main shaft and its blades is located at the bottom.
  • The two gaskets that are pictured are of the upmost importance to ensure that the mixing of fuel and oil does not occur. These gaskets and/or main shaft oil seal are the known to cause issues with the cross contamination of the fuel with oil.

Common faults with VAG vehicles with tandem fuel and vacuum pumps
Main pump shaft and blade

6- Remove the pumps main shaft, which has a press fit.
Replace the pumps main shaft seal.

Common faults with VAG vehicles with tandem fuel and vacuum pumps
Left picture: Main pump shaft - Right picture: Pump Shaft oil seal

- Once the gaskets and oil seals described in procedures 5&6 have been replaced, re-assemble in the reverse order.

7- Prior to refitting the overhauled assembly it is essential that the gaskets at the base of the pump must be replaced where the tandem pump locates on the cylinder head.

Common faults with VAG vehicles with tandem fuel and vacuum pumps
Gaskets at the base of the pump

*Note: some pumps use a metal gasket instead of the two gaskets shown in the above image.

8- Refit the pump on the cylinder head. Tighten the top bolts (Allen 6) to a torque of the 20 Nm, the two bottoms bolts (Allen 5) should be tightened to 10 Nm.

 

6 comments:

  1. Hi, interesting post. I have a question: I currently have in the workshop an Audi A3 TDI with ATD engine. I have a problem with starter. My diagnostic scanner indicates no failure. If I put Ether and the engine is starting, it seems to be an air intake, the tandem pump is losing gasoil, but I don´t know if it is its fault that engine is hardly starting. I checked the diagram which indicates that there is an elevating pump in the tank, so what gasoil pressure should I get in the gasoil filter? It can take air from the tandem pump; once the engine started the car is functioning well during the day. This problem is happening again the day after. The problem could come from the elevating pump which is not working properly, and tandem pump can´t bring gasoil so engine has problems to start. Thanks for the blog, very interesting content. Ramón

    ReplyDelete
    Replies
    1. Good morning Mr. Ramon,

      As Antonio B. just said, if the vehicle loses gasoil regardless it is or not the failure cause, that would be the first problem to solve. If tandem pump is losing gasoil, this post will be helpful for you.
      Once the gasoil loss problem is solved, if the failure remains, it could come from others causes like air intake in some pipes or gasoil filter, intake air from gasoil radiator located under the vehicle in the right part, or gasoil electric pump with fuel tank gauge.

      I hope that we have been helpful.
      Guillermo Estébanez, Grup Eina Digital.

      Delete
  2. If it loses gasoil, that’s the first problem you should solve, either it is the failure cause or not. If it loses gasoil when starting, it can take air when there is no pressure and the engine is stopped. Antonio B.

    ReplyDelete
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  5. I had zero clue that there were so many different types of vacuum pump out there. I always thought most of them worked about the same, and was completely oblivious to the fact that the interior of them looked so different. I’m looking to get a vacuum pump for a project that I’ve got coming up, but now I know I probably need to do some more research. Thanks for sharing!

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