Fuel Pumps

[Shoppinit]

Just to be crystal clear, shall I just take out the PCVs and connect the open hoses? Or let them open?

I would block, using a plug of some sort, pipes 2 and 3. The other side you can leave open. Slightly pressurised blow-by will vent from the crankcase / cam covers.

Pipe 26 could be blocked where the non-return valve is.

The idea is to block as close to the admission points as possible to eliminate as much of the plumbing as possible. The other side can remain vented to atmosphere.

Ideally you'd block up the hole to the inlet manifold and the holes to the admission upstream of the turbos, but this might not be practical in terms of accessibility.

[Shoppinit]

Make sure you don't block anything that would cause pressure to increase in the crank case / cam covers. You block the inlets but *not* the outlets from the block / cam covers.

[Classik]

Make sure you don't block anything that would cause pressure to increase in the crank case / cam covers. You block the inlets but *not* the outlets from the block / cam covers.

Well noted, thanks! I'll try the test 2 posts above ^^

[Classik]

Sorry, no news 'cause no time for testing yet..
Meanwhile I'm trying to get a comprehensive understanding of the car's plumbing In particular I'm curious about those hoses 49 & 50, where are they going to?

[Shoppinit]

The solid pipes 41 and 43 look like the ones going to upstream of the turbos. They are recycling the air diverted from the DVs. 49 and 50 are where the PCV feeds back into the air stream upstream up of the turbos.

[Classik]

Thank you Shopp!

So if I understand well, the whole vaccum system is fed by the succion pipes 41 & 43 (ref to the image above^^, not the one below) using a Venturi effect created by the air flow going to the turbo, right? Surprisingly 41 & 43 are not totally symetrical as part 41 has all these small branches that do not exist on 43 but I suppose the smart engineers at Audi have taken care of this.

Having said that I had a chance to make the suggested tests you mentionned a few posts above, namely blocking pipes 2 & 3. In short it helps to slightly compensate for the difference between the MAFs readings, but not to the point of aligning them. To give you more detailed figures, at idle MAFs read 2,60 g/s on Bank 1 and 3,5 g/s on Bank 2, whereas with the PCV circuit blocked Bank 1 reads around 2,95 g/s and Bank 2 remains more or less the same at 3,5.

So we're still not there, but I still believe some dirt must be blocking those pipes/hoses/non-return valves coming upstream of the turbos. I'm tempted to throw some brake cleaner in there but something tells me it's not a good idea, so maybe you would have an idea to clean those pipes in place?

[Shoppinit]

Not so much Venturi as just negative pressure from the compressor. Vacuum is coming from there (almost always) or from the inlet manifold at idle when the butterfly valve is pretty much closed. Much of the plumbing in the PCV, N75, N80 and N249 is to deal with the varying pressure conditions in the inlet.

There’s also a vacuum reservoir thrown into the mix.

It’s interesting that bypassing the PCV improves the imbalance. Seems like it’s worth cleaning it all out. I wouldn’t blast carb or brake cleaner in there. Bit like playing Russian roulette if a chunk comes off and obliterates your turbine. That would be a bad day. Depends how lucky you are feeling.

I think the pipes are going to have to come off, or at least disconnect both ends before soaking in brake cleaner and blowing through with compressed air.

3 and 3.5 isn’t a huge difference. Were you able to log while driving with the PCV bypassed?

[Classik]

Thanks for the education Shopp, this is very much appreciated! So if I understand well, most of the negative pressure work is done by the turbos through pipes 11 & 43 connected to the turbos and controlled by the N75 valve? And yes, I've also noticed the vaccum reservoirs.



Regarding the carb cleaning, yes that's what I thought too, too risky... But I was dreaming of a tool like a flexible hose with external brushes that I could connect to a vaccum cleaner, which would permit to suck out the dirt as you progress inside the pipes, a bit like this:


In all cases, unmounting the pipes would be the best route, but I can't see how this could be done without removing the engine from the car.

And no I didn't log whilst driving, I'll try to do that asap.

Can't say enough many thanks for your help & expertise!

[Shoppinit]

You might be able to disconnect the small flexis (10) from the inlets and flush the pipes with copious amounts of carb cleaner. You might be able to get your hands down the back of the engine. They’re visible at least. It’ll be messy, but also least it won’t run into the turbos. You could use your pipe cleaner, possibly. I’d be a bit wary of compacting the crud into a total blockage, though. I guess you could use a borescope to check.

[Classik]

Thanks for your patience Shopp, same excuses for late reply on your last post : loads of work and a family to care for... Finally had a chance for more pipes cleaning and some more tests. In short, it's still not solved but there's clearly some progress.

1/ As my MAFs connectors were in bad shape, I had them rewired but did ask for a 10cm extension on each side. This way I'm now able to swap the connectors between MAFs. The verdict is clear : it's definitely a mechanical problem, nothing to do with the wiring, ecu or whatever ground / resistance issue.
2/ Following my last pipe cleaning campaign, the fault code related to the MAFs discrepancies has not reappeared yet, which is obviously great news indeed!! More precisely the MAFs reading at idle are still not good (20-40% difference) but under load they seem to behave better. I'll come back with more precise measurements to substantiate this.
3/ Fuel trims, lambdas are still perfectly aligned (they always were, but glad it's still the same)
4/ Cats on both side have the same temperature so the clogged cat possibility should be ruled out

In addition to the above points, my mapper suggested a few routes to follow :
a/ swap dump valves as they may not be properly calibrated (actually I've changed them for new oems, but didn't swap them within a pair). Although the probability is low that this could be the source of the problem, it's quite easy to try
b/ test compressions : already discussed with Shoppinit. If compression on a cylinder was that bad to allow for such discrepancies, the engine would run very badly. Nevertheless it's always good to evaluate the sealing.
c/ discrepancies between turbos : after 160,000km of use, turbos may not perform equally and according to my mapper this could well explain the difference between MAFs. How does that sound to you?

[Shoppinit]

Turbos might be unbalanced but since the problem is apparent at idle and low revs it’s much more likely to be a vacuum problem IMO.

Did you ever swap back old the wastegate actuators?

Since your cleaning is having obvious beneficial effects I would suspect that possibly your partial blockage might have caused blow-by to pass onto other vacuum systems, possibly inhibiting their operation. I think I would persist in the cleaning and also investigate the vacuum components under the manifold. Non-return valves, suction jet, etc.

[Classik]

Thank you for the continued interest and suggestions!

Turbos might be unbalanced but since the problem is apparent at idle and low revs it’s much more likely to be a vacuum problem IMO.

This was my reply as well; his point is that even at idle turbos are spinning (admittedly slowly), but probably enough to push a few g/s of air into the system, which is the order of magnitude of the MAFs discrepancies.

Did you ever swap back old the wastegate actuators?

Actually I did! So except if I'm particularly unlucky (=both wastegate pairs are unbalanced AND installed the same way), it didn't change anything.

Since your cleaning is having obvious beneficial effects I would suspect that possibly your partial blockage might have caused blow-by to pass onto other vacuum systems, possibly inhibiting their operation. I think I would persist in the cleaning and also investigate the vacuum components under the manifold. Non-return valves, suction jet, etc.

My thoughts exactly!
Since I intend to open the intake manifold, are there any other jobs I should envisage in the 'since I'm there' spirit? Of course change the flat metallic manifold seals, but i remember a repair kit for the injectors (o-rings + other small bits), except if some of you have tried upgraded injectors with success?

[Shoppinit]

You might want to replace the V51 after run pump. It can fail (often without symptoms) and it’s extra protection for the turbos. I’m sure that, like me, you cool your engine down completely before turning it off, but it neve hurts to have a working V51.

You could replace the injector seals. In for a penny, in for a pound.

[Classik]

Absolutely, I do take the time required to cool the engine down, but nevertheless a working coolant after run pump is in order, thanks !
Sorry to insist on the subject, but have you heard anything about a successful injectors upgrade? Since I'm running e85 which induces more fuel consumption, this may be a good time to upgrade, what do you reckon?

[Mɐʇʇ]

I've actually got all the bits in a box (pump, manifold gaskets etc) to replace mine - but I can still hear it whirring after a run so have left well alone. I just bought all the bits "in case"
I also kinda came to the view that making sure to run the engine lightly loaded for the last mile or 2, let it idle down a bit, and regular oil changes are the keys to longevity.

You might want to replace the V51 after run pump. It can fail (often without symptoms) and it’s extra protection for the turbos. I’m sure that, like me, you cool your engine down completely before turning it off, but it neve hurts to have a working V51.

You could replace the injector seals. In for a penny, in for a pound.