PlasticMac
Member
There have been two confirmed cases of a partial failure of the tank end electric tank lift pump, causing symptoms that don't immediately point to fuel pressure, nor the electric lift pump.
There were a few mentions of similar symptoms in both threads, some where the ProBoost map was fitted. The Proboost overrides some of the FSI engine's contentious features, but the fuel system is not one of them.
The first instance caused the car not to start when it was hot. The second caused "bogging down" and a lack of power at high revs, and a feeling that the engine was straining.
The hot start troubles were traced to the electric lift pump being down on pressure. It was OK when the car was running, when the electric pump pressure is limited it to 3.0 Bar, but could not deliver the 5.8 Bar required to prevent the fuel vaporising in the line to the high pressure pump, (and forming bubbles).
The "bogging down" symptoms cleared when the electric pump was replaced,
The FSI has two fuel pumps, one is an electrically driven, lift pump, located under the rear passenger seat on the driver's side, and feeds petrol under pressure to the input side of the high pressure fuel pump, mounted on, and driven by, the engine.
The output of the high pressure pump is totally dependant on the pressure at the input. If the input pressure is low, (less than 3 Bar when engine is running), the pressure to the fuel rail, and injectors will also be low, (less than 100 Bar).
The lift pump in the tank generates 5.8 Bar, but in normal running a bypass valve, (N290 valve, misleadingly called a "fuel metering valve" by Audi) limits it to 3.0 Bar. The mechanical, high pressure pump generates 100 Bar, but only if the electric pump is fully working.
The high pressure, approx 100 Bar, can be checked with VCDS via Groups 140 and 141. The output of the electric pump is not monitored, so a pressure gauge is need to check it. *This check would need to be done with a hot engine, ignition ON but engine not running, when pressure should be approx 5.8 Bar.
I have posted these notes, as it would be easy to assume the, (very expensive), high pressure pump is at fault, when the problem could be the, (much cheaper), electric lift pump.
If you think about it, an electric pump, running for thousands of hours, is going to get a bit tired after 15 plus years!
My suggestion is that if your FSI is a bit "off colour" checking the electric pump pressure, or maybe fitting a used spare as a trial, would be a good idea. The part number is 8Z0919051C, and seems to be widely used across the VAG group.
*It would be easier and safer to check the electric pump off the car, using a safer fuel, such as kerosene.
Mac.
PS: If you spot any errors, or lack of clarity, (or is that only for politicians?), please let me know.
There were a few mentions of similar symptoms in both threads, some where the ProBoost map was fitted. The Proboost overrides some of the FSI engine's contentious features, but the fuel system is not one of them.
The first instance caused the car not to start when it was hot. The second caused "bogging down" and a lack of power at high revs, and a feeling that the engine was straining.
The hot start troubles were traced to the electric lift pump being down on pressure. It was OK when the car was running, when the electric pump pressure is limited it to 3.0 Bar, but could not deliver the 5.8 Bar required to prevent the fuel vaporising in the line to the high pressure pump, (and forming bubbles).
The "bogging down" symptoms cleared when the electric pump was replaced,
The FSI has two fuel pumps, one is an electrically driven, lift pump, located under the rear passenger seat on the driver's side, and feeds petrol under pressure to the input side of the high pressure fuel pump, mounted on, and driven by, the engine.
The output of the high pressure pump is totally dependant on the pressure at the input. If the input pressure is low, (less than 3 Bar when engine is running), the pressure to the fuel rail, and injectors will also be low, (less than 100 Bar).
The lift pump in the tank generates 5.8 Bar, but in normal running a bypass valve, (N290 valve, misleadingly called a "fuel metering valve" by Audi) limits it to 3.0 Bar. The mechanical, high pressure pump generates 100 Bar, but only if the electric pump is fully working.
The high pressure, approx 100 Bar, can be checked with VCDS via Groups 140 and 141. The output of the electric pump is not monitored, so a pressure gauge is need to check it. *This check would need to be done with a hot engine, ignition ON but engine not running, when pressure should be approx 5.8 Bar.
I have posted these notes, as it would be easy to assume the, (very expensive), high pressure pump is at fault, when the problem could be the, (much cheaper), electric lift pump.
If you think about it, an electric pump, running for thousands of hours, is going to get a bit tired after 15 plus years!
My suggestion is that if your FSI is a bit "off colour" checking the electric pump pressure, or maybe fitting a used spare as a trial, would be a good idea. The part number is 8Z0919051C, and seems to be widely used across the VAG group.
*It would be easier and safer to check the electric pump off the car, using a safer fuel, such as kerosene.
Mac.
PS: If you spot any errors, or lack of clarity, (or is that only for politicians?), please let me know.
