Looking for help / High pressure fuel pump 1.6 FSI

Sorry, I can't yet. I wasn't there when the test was done.
Some kind of assisted start has been used here. I think. I will ask about it at the beginning of next week.
Suspect it might be using an aerosol "starting gas"
Not a good idea, it can burn very hot and damage the engine.
Mac.
 
The difference between a cold start and a hot start is that during a hot start, the electric pump is expected to deliver 5.8 bar. Normally, it runs at 4.0 bar.
Also during a hot start, the fuel metering valve is closed for a short time, (50 seconds), to increase pressure in order to prevent bubbles, (Edit: fuel vaporising due to temperature), in the fuel flow.
Since your problem is with hot starts, investigate the electric pump pressure when hot. I don't think there is a sensor on the output of the electric pump, so if it were a problem, no error would be seen.
You should read about the fuel system in SSP235, starting at page 31.
Mac.
 

Attachments

  • SSP_253 FSI_Engine.pdf
    1.6 MB · Views: 80
Last edited:
Maybe I can explain a bit. Petrol has a low boiling point, (the temperature at which it turns to vapour), at normal ambient it's ok, but as temperature increases, it is more likely to boil/vaporise.
Putting petrol under pressure raises the boiling point, (like a pressure cooker). The logic in the FSI Fuel system is that in order to ensure the fuel doesn't vaporise before it gets to the high pressure pump inlet on a hot engine, the electric fuel pump runs at a higher pressure than normal, 5.8 Bar not the normal 4.0 Bar.
In @VVVVVV car, the high pressure pump is working fine, once the engine is running, so it's probably OK. my guess is that the electric pump is not producing 5.8 Bar when the engine is hot, so the fuel supply to the high pressure pump is vaporising, and the ECU produces a low pressure DTC for the high pressure pump as a result of vapour at the inlet. Once the engine running, all is well, as cooler fresh fuel is drawn from the tank.
The electric pump is either faulty, or the fuel metering valve is not closing as it should for a hot start.
Mac.
 
Last edited:
Maybe I can explain a bit. Petrol has a low boiling point, (the temperature at which it turns to vapour), at normal ambient it's ok, but as temperature increases, it is more likely to boil/vaporise.
Putting petrol under pressure raises the boiling point, (like a pressure cooker). The logic in the FSI Fuel system is that in order to ensure the fuel doesn't vaporise before it gets to the high pressure pump inlet on a hot engine, the electric fuel pump runs at a higher pressure than normal, 5.8 Bar not the normal 4.0 Bar.
In @VVVVVV car, the high pressure pump is working fine, once the engine is running, so it's probably OK. my guess is that the electric pump is not producing 5.8 Bar when the engine is hot, so the fuel supply to the high pressure pump is vaporising, and the ECU produces a low pressure DTC for the high pressure pump as a result of vapour at the inlet. Once the engine running, all is well, as cooler fresh fuel is drawn from the tank.
The electric pump is either faulty, or the fuel metering valve is not closing as it should for a hot start.
Mac.
Fantastic!

I'll talk to the mechanic tomorrow about it. I had already looked for a few alternative high-pressure fuel pumps.
But if the fault is the electric fuel pump (number 2 in the PDF material you sent), it will be easier... if it is not also really rare part for the car.

This is really kind and well explained help 🙌 thank you!
 
It's Alive! It's Alive!
It really was an electric fuel pump. In addition, there was a really small hole in the hose leaving it, from which the pressure has managed to escape even on the way. Thanks everybody and Special thanks @PlasticMac for from detective work.

Time to Hit The Road Again 🫡
 
It's Alive! It's Alive!
It really was an electric fuel pump. In addition, there was a really small hole in the hose leaving it, from which the pressure has managed to escape even on the way. Thanks everybody and Special thanks @PlasticMac for from detective work.

Time to Hit The Road Again 🫡
Fantastic. Enjoy the revs!
Mac.
 
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