B7 fuel lines

[VWSHPFRMN]

I have been asked by several members to explain the fuel lines on the B7 TDI engine. There is no longer a return to the tank from the filter. The boost pump has been eliminated. Fuel is supplied from the tank to the filter. From the filter the fuel is supplied directly to the HPFP. From the HPFP fuel is supplied to the fuel rail. From the rail fuel is supplied to each injector. Fuel return goes as follows. From the fuel rail unused fuel is retuned to the fuel filter. From the HPFP and the injectors unused fuel is returned directly to the tank. It is my belief that the hot fuel from the rail is returned to the filter to heat the fuel.

 

[740GLE]

Finally someone else questioning the changes between the CJAA and the "whatever the code of this one is" beyond the fancy urea.

My guess is they prob switch up how the returns go depending on fuel temp registered near the HPFP (CJAA has a similar temp sensor). So on a cold morning the rail bleed goes directly to the FF, and when the temps of the fuel get hot enough, the majority or 50/50 of the bleeding goes directly back to the tank as a giant heat sink, this way it'll keep the fuel going into the HPFP near an designed operating range.

 

[VWSHPFRMN]

The engine code is CKRA

 

[eddif]

Thanks for starting the thread.

Can you give us some rough pressures for the various places? Is the lift pump pressure higher? Is there a secondary pump inside the HPFP, or is the tank pump multi pressure? Is there a fuel return strainer / screen / filter?

Is there an online drawing / manual for the changes?

Thanks again

eddif

 

[VWSHPFRMN]

The lift pump delivers 6 bar of pressure. A valve in the HPFP reduces the pressure to 5 bar. There is no secondary pump in the HPFP. I did not see any strainers or screens in the lines but that does not mean they don't exsist. I do not have the HPFP pressure specs at this time.

 

[eddif]

The lift pump delivers 6 bar of pressure. A valve in the HPFP reduces the pressure to 5 bar. There is no secondary pump in the HPFP. I did not see any strainers or screens in the lines but that does not mean they don't exsist. I do not have the HPFP pressure specs at this time.

Here I go again guessing.

The new tank mounted pump has about the same pressure as the old boost pump (makes sense to keep everything working almost the same).

The only sensible method of warming is with the rail pressure control bleed off fuel. When the fuel is cold the pressure bleed may be greater and when warm the flow should be lower (?).

The old method of using the HPFP return line will not work to warm the filter, because the pressure would be too low from the HPFP. So now the HPFP return just heads for the tank.

The major effective change is that: the boost pump output has been changed from a screen to a filter. The HPFP gets filtered fuel rather than screened fuel.

See some of you at the HPFP thread to discuss some of this.

Thanks for the information, and I hope I drew no wrong conclusions.

eddif

 

[abctdi]

The major effective change is that: the boost pump output has been changed from a screen to a filter. The HPFP gets filtered fuel rather than screened fuel.

If so, then better to be filtered than just screened. Not sure this will completely fend off all failures though.
New owners take heed...don't put gasoline in your tank, ever.

 

[eddif]

If so, then better to be filtered than just screened. Not sure this will completely fend off all failures though.
New owners take heed...don't put gasoline in your tank, ever.

The problem with the putting of gasoline in the owners tank is not always under the owners control. Transport accidents, stations using gasoline to stop bacteria fungal growth, all sorts contamination beyond the driver / operator.

Much of the conversation about additional filtering is because some failures will take place because of factors beyond the owners control (lack of equipment robust design through mixed fueling and other contaminates). With additional filtering the $8,000 USD failure is reduced to a $2,000 failure. Not great, just better.

eddif

 

[pleopard]

I assume this engine continues to use piezo injectors? I see they're no longer fed directly down the center axis of the injector but from the side at an angle. This engine also appears to be used in the European Tiguan and the North American Audi A3.

 

[740GLE]

The first batch of Audi A3's had the same engine code, CEBA, as the 2009 Jettas. I thought it has always been the same as the Jettas. You have any other info on this?

 

[oilhammer]

I assume this engine continues to use piezo injectors? I see they're no longer fed directly down the center axis of the injector but from the side at an angle. This engine also appears to be used in the European Tiguan and the North American Audi A3.

The new Passat's engine uses different injectors, and as I understand they are solenoid operated, not piezo.

 

[740GLE]

Have newer solenoid injectors increased their injection frequency? I thought the reason they had to go piezos was for the 7 injections per cumbustion cycle, each a different volume. No solenoid injector could fire so fast as well as change the displacement of the injection. Piezo multiple injections, not only smooths out the clater, but also is a major player in meeting emissions requirements.

 

[oilhammer]

This is all news to me, too. And may be wrong. I do know the part number for the injectors IS different, and they DO look different.

 

[pleopard]

I'd be quite surprised if they went back to solenoid fired injectors. The injectors are different, but probably just a different configuration to accommodate the new fuel line arrangement VW went with. However, this is clearly quite a major fuel system update in one way or another.

I have no specific info on the 2012 A3 TDI, but saw a photo on audi.ca showing the same engine cover with the oil fill cap on the right side.