S3 fueling issues

[S38PG]

Hi everyone! Got a bit of a problem with my S3 8P BHZ. On stock software, the car is running great, however when stage 1 is applied, HPFP starts to struggle hard and rail pressure drops massively.

Mods wise, car has a 3" downpipe with middle section, RAMAIR intake and red top coils. Fuel filter and cam follower have been changed along with the usual maintenance items. HPFP and PRV are stock.

So far I've received suggestions such as "lazy" O2 sensor, sending data to the ECU with a delay, injector issues and faulty PRV. What do you think?
Log: https://log.tunezilla.com/chart/688...DgEtAcMObKMOOJm0qw5l+wrfCrg/DoQN1wqhzSMKjAAAA

 

[bronco]

After my down pipe got installed, I was getting CEL on with O2 sensor error. I had an "extender" installed and problems went away.

However, I never had any fuelling issues with Stage 1 tune and stock HPFP.

 

[prt57]

It maybe that rather than stage 1 software stage 1+ has been applied. On true stage 1, the HPFP should be fine. However stage 1+ requires more fuel and so an uprated pump or pump internals is fitted.
Another thing to think about is the rubber pipe connecting to the bottom of the HPFP. If it has ever been disturbed there is a chance that small pieces of rubber break off and clog or partially clog the inlet to the pump. Maybe enough fuel gets through as standard but not enough when mapped. Always sensible to replace the rubber pipe if it has ever been disturbed, especially as your car is at least 15 years old being a prefacelift.
And finally, there is a modification to the brass inlet mentioned already. As standard, it has an inlet hole that is approx 1mm in diameter. The modification is to increase the diameter to 5mm. Less restriction to the HPFP. This will also help the LPFP as at least 15 years old it maybe a little tired. Do some research on the 5mm drill modification

 

[S38PG]

It maybe that rather than stage 1 software stage 1+ has been applied. On true stage 1, the HPFP should be fine. However stage 1+ requires more fuel and so an uprated pump or pump internals is fitted.
Another thing to think about is the rubber pipe connecting to the bottom of the HPFP. If it has ever been disturbed there is a chance that small pieces of rubber break off and clog or partially clog the inlet to the pump. Maybe enough fuel gets through as standard but not enough when mapped. Always sensible to replace the rubber pipe if it has ever been disturbed, especially as your car is at least 15 years old being a prefacelift.
And finally, there is a modification to the brass inlet mentioned already. As standard, it has an inlet hole that is approx 1mm in diameter. The modification is to increase the diameter to 5mm. Less restriction to the HPFP. This will also help the LPFP as at least 15 years old it maybe a little tired. Do some research on the 5mm drill modification

AFAIK the HPFP should keep up until stage 2, anything more than that would require an upgrade. In my case, it gives up completely as soon as more boost is requested.
LPFP seems to be performing adequete throughout the rev range, without pressure drops. Duty cycle at idle is around 45-48% so it should be fine.
When it comes to the rubber hose, I don't think its ever been changed, so it makes sense that it could be detoriating and clogging up the HPFP. Do you know the part number, by any chance?

 

[ch1z64]

AFAIK the HPFP should keep up until stage 2, anything more than that would require an upgrade. In my case, it gives up completely as soon as more boost is requested.
LPFP seems to be performing adequete throughout the rev range, without pressure drops. Duty cycle at idle is around 45-48% so it should be fine.
When it comes to the rubber hose, I don't think its ever been changed, so it makes sense that it could be detoriating and clogging up the HPFP. Do you know the part number, by any chance?

I run a st1 and have an upgraded HPFP with APR internals plus i av a RS4 prv valve inserted which helps the fuel pass through ,

Sent from my SM-G970F using Tapatalk

 

[prt57]

AFAIK the HPFP should keep up until stage 2, anything more than that would require an upgrade. In my case, it gives up completely as soon as more boost is requested.
LPFP seems to be performing adequete throughout the rev range, without pressure drops. Duty cycle at idle is around 45-48% so it should be fine.
When it comes to the rubber hose, I don't think its ever been changed, so it makes sense that it could be detoriating and clogging up the HPFP. Do you know the part number, by any chance?

I agree that the HPFP is OK at stage 2 but stage 1+ requires more fuel to give the boost in mid range torque.

Genuine VAG 2.0TFSi High Pressure Fuel Pump Hose - 06F127511B

Genuine 2.0TFSi HPFP Hose

www.akstuning.co.uk

 

[S38PG]

I agree that the HPFP is OK at stage 2 but stage 1+ requires more fuel to give the boost in mid range torque.

Genuine VAG 2.0TFSi High Pressure Fuel Pump Hose - 06F127511B

Genuine 2.0TFSi HPFP Hose

www.akstuning.co.uk

I thought stage 2 would request more in terms of fuel and boost than stage 1+?
How much boost does stage 1, 2 and 2+ require? What about rail pressures between all stages?

Thanks for the link, hopefully I'll see some improvement after replacing this hose.

I run a st1 and have an upgraded HPFP with APR internals plus i av a RS4 prv valve inserted which helps the fuel pass through ,

Sent from my SM-G970F using Tapatalk

That's the proper way of doing things, I agree. I will upgrade the fueling in the future for sure but I wanted to do it in stages. Guess that wouldn't work.

 

[prt57]

Do some research on the 5mm pump inlet modification. Uprated pumps like the Loba already have this done.
A word of warning in that you undo the brass inlet Barb, there is a little sealing washer behind that is easy to loose. If lost, you will have a leak and I don’t think it is available to buy.

 

[prt57]

 

[nluk100]

I had an issue with my std FPV at stage 2 on my S3, they must not like being pushed too much. For the sake of a £50 RS4 I would swap it out.

 

[ch1z64]

I had an issue with my std FPV at stage 2 on my S3, they must not like being pushed too much. For the sake of a £50 RS4 I would swap it out.

U know the way i do , they will do om cheap and always ask what the Fu* k is wrong ?

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[S38PG]

Log shows that after 6k, car is passing 120bar spec/actual, so PRV is less likely to be faulty, no?

Thanks for your inputs, the rubber hose has been ordered and I'll do the 5mm mod first. HPFP and RS4 valve will follow shortly.