S2 Coupe Down Under

[Tractor Dave]

Interesting thing Dave - now I can swap fuel pumps with relative ease, I put the stock Bosch back in today and everything is back to normal . Looks like I'll be saving the Walbro until I do any mods. I can only assume it was overwhelming the FPR.

As you say. Very interesting. I know of quite a few who have upgraded to the Walbro with no issues and i have the Rs2 Pierburg again with no issues. Was your tank pressurised? I wonder if the issue was the return pipework or tank venting\carbon canister?

[Solfella]

As you say. Very interesting. I know of quite a few who have upgraded to the Walbro with no issues and i have the Rs2 Pierburg again with no issues. Was your tank pressurised? I wonder if the issue was the return pipework or tank venting\carbon canister?

No evidence of the tank being pressurised Dave. I did wonder if it exposed another issue yet to be identified, but I'm no more than second guessing. However, I have taken to increasingly using AI in conversation to discuss various car related issues, mods, etc. A recent query response suggested that, '... a high-flow Walbro 450 fuel pump in a completely stock Audi S2 can cause issues. While a stock fuel pressure regulator (FPR) tries to bypass the extra volume, a 450lph pump can overwhelm factory return lines ...', and this seemed to be corroborated on other forums. I'm a way off upgrades and a remap yet. It will be interesting to see if the issue reemerges at that time.

[Solfella]

Plugged away at some loose ends over the weekend, largely trying to remember what interior trim goes where, with what screws and in what order. Had cause to replace the indicator stalk mechanism, which wasn't but is now self cancelling, and came across a rather dodgy looking airbag connector , so repaired that.

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Then I washed the car ... water pouring in through the sunroof, of course. Quick search on the forum found the likely culprit, following descriptions by newsh in this forum thread.

Looks like I need a new drip tray, which had disappeared down the back of the casette. Fished it out with a coat hanger. Thankfully, available on Tradition and ordered last night.

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[Solfella]

Drip tray arrived so I fitted it. As in the description from newsh, removed the sunroof headliner and three star headed bolts either side of the sunroof, which then easily lifts out.

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Removing the screws from along the top of one of the rails enables the drip tray, now hooked under the opposite rail, to slide under the rail where the screws are removed. Initially I removed all the screws but then found leaving the two closest to the front of the car in place left enough flex in the rail to lift it at the rear edge of the sunroof opening just enough to allow the drip tray slider to go under, while also enabling me to manually operate the roof mechanism. This is needed to get to a screw that is hidden by the tilt mechanism depending on the sunroof position.

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Once the drip tray is in place and the screws back in (I injected a small amount of sealant into each hole before fixing the screws), the arms for the drip tray just click into place, here at 10 o'clock to the last empty screw hole.

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Then it's a case of refitting the sunroof and the sunroof liner. I marked the star headed bolts before I removed them but found that this wasn't necessary in my case - the sunroof went back in with no adjustment needed.

Meanwhile STILL waiting for my windscreen. Pilkington Classics said it was in the UK and will be shipped this week but no news as yet. 26 weeks since ordering now.

And after initially thinking it had, and with two different fuel pumps, my hesitation/stumbling under load hasn't gone away. Typically, I can build revs slowly and everything seems fine but once pushing harder the car starts to stutter as if it’s struggling for fuel, ignition or boost. This often happens on the 4K rev area, once boost starts to build, or pulling away hard from standstill. Going to WOT seems impossible. It might be me, but fuel economy seems to be suffering too. Car starts on the button. Issue seems worse when the car is warm.

I'm quite sure this is a consequence of me changing fuel pumps and somehow causing the issue, so mea culpa. I have another fuel filter so I could try that but then I'm out of ideas. So coincidental, an error on my part, or has that short period on the higher flow pump uncovered another weakness, have I disturbed or damaged something else when the interior was out? I just don't know but it's driving me nuts.

Mechanics with classic Audi knowledge are very thin on the ground in Far North Queensland but I went to a local independent servicing German cars here the other day who was very enthusiastic about my 'unicorn car' as he described it, so it's booked in to be looked at in a couple of weeks.

[Tractor Dave]

I would do a flow test as per the manual and see what you are getting.
next is all the usual culprits. Boost leak, vac leaks, maf pins, coil packs, spark plugs, timing.
In all the cars i have done i have had this three times. Once it was timing, once faulty new fuel pump and once a boost leak.

[hashluck]

Per Tractor Dave, what feels like a fuel issue may easily be something else, such as ignition or boost leaks. Smoke test will rule out the latter but could still be the Diverter Valve or N75 Valve (both available and easily replaced). That said, your description and that it feels a bit like fuel leads me to suspect coil packs. These are a when not if fail item and if you are on the originals I would be looking here (or the power amps on the firewall). When they begin to fail it can easily be only when under load or WOT and feel like a hesitation. Hopefully your guy can work through everything methodically and logically. It could also of course be a combination of any or all of the above!

[Solfella]

Thanks fellas. Yes, I realise it could be fuel, or ignition, or boost, or vacuum or a combination, etc. Because I've been messing around with the fuel delivery, that's inevitably my first suspect, but I appreciate I could be wrong. Unfortunately, outside my immediate abilities to diagnose. I can at least do a flow test so will try that. Plugs were changed with no difference. I had plans to change to TFSi anyway, but don't at this stage know if the current coils and/or POS are failing. I am waiting for TFSi cols and harness to arrive as we speak.

[RedV6]

Great work on the sun roof. Had to repair ours (see V6 just needs a bit of polish). See pic of sunroof tray removed, hopefully its a useful pic.
I do have a video of it working out of the car but I can't upload it for some reason. Anyway here is a screenshot from the vid!

[Solfella]

Great work on the sun roof. Had to repair ours (see V6 just needs a bit of polish). See pic of sunroof tray removed, hopefully its a useful pic.

Very useful - one can clearly see where the drip tray fits. At one point I could have removed the whole cassette like you have but that was, of course, before I put the headlining and half the trim back in.

Following your 'bit of a polish' with interest. Great stuff.

[Solfella]

Well, what a few weeks it's been.

Windscreen finally arrived from Pilkington, 28 weeks after ordering it -YAY!

Took it to get installed and the fitter cracked it on installing the A pillar covers - ARGGHHHH! ARGGHHHH!

So back to square one but at the least the next screen is on the installer's insurance, not mine. Just gotta wait the 15 weeks from Pilkington (hoping it won't be another 28).

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Meanwhile ... car came back from an independent who I asked to look into the hesitation/stumbling under load. They smoke tested the system. No issues with boost or vacuum leaks.

Made up a fuel pressure gauge and monitored the car, which showed a drop off in fuel pressure under load. After checking other parts of the fuel system, they wondered if it might be fuel pump, debris in the system, or voltage drop. The latter was ruled out so I have the car back home to look at the debris and/or fuel pump issues. I decided to start by removing and cleaning the tank.

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Before:

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During:

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After:

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Also found perishing in the flexible hose connecting the pump to the fuel line but not sure how problematic it is. Either way, will replace with new.

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Blew out all the fuel lines from the tank to the filter but no immediate evidence of those being clogged at all. Next step is to put it back together with a new pump and clean fuel and see where we are. I've also got the parts to upgrade to TFSi coils so that will be soon also.

Hey, ho.

[Solfella]

Fitted the cleaned out tank today, along with a new Walbro GSS352 I picked up fairly cheaply. Followed the description in this thread to remodel the basket to take the pump and fuel filter sock.

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All went back together well, took the car out for plenty of WOT and full boost and now all seems back to normal with no hesitation under load. I can't identify exactly what made the difference as I changed several variables - cleaned the tank, changed the pump and filter pick up, replaced the flexible pump to fuel line connector, and blew out the fuel lines between fuel filter and pump.

Will now be interesting to see what difference replacing the fuel tank cover, boot carpet and seats make as the pump is quite noisey with a high pitch whine, especially at idle - it quietens down under load though.