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Good day all,

Probably haven't searched enough, but I haven't seen many threads on the subject. After 160,000km I'm getting what I suppose being signs of fuel pumps ageing : lean mixture faults under load (not good), MAF performance issues (although they are 6 months old - Bosch as they should, and no problem when engine is idle), and the general impression I'm not getting the full power from the car.

Of course my first question to the veterans would be: how can I confirm this is indeed a pump performance issue. I have the VCDS HEX NET and should be able to create all sorts of logs (in particular ch 32 which always shows positive fuel trim adaptation = lean mixture).

Then the next question is getting recommandations for replacing those pumps. So far I've been recommanded the Bosch 044 for the external pump (next to the fuel filter), and the Walbro 450lh 274 (or alternatively the 267) for the one located underneath the rear right passenger seat. What is the last word on the matter? Any difficulties for the installation (size,...)?

Many thanks!

PS: still working on the secondary fan ECU issue, more news later...

Annoyingly the RS6 doesn't have a fuel pressure sensor so that makes it difficult to check pressure, especially under load.

It could be a bad fuel pump, or a bad fuel pressure regulator, or a blocked fuel filter. Could be a blocked carbon canister / evap problem which is causing incorrect venting of the fuel tank. That one's easy to eliminate - just do a test without the fuel filler cap on. Careful, though, the fuel could slosh out if you're not careful.

Don't know about aftermarket pumps. Unless they were a lot cheaper then I'd probably just go OEM.

What is your issue with the MAFs? They should be completely independant of the fuel pump / pressure. Smells fishy.

Thanks for the detailled reply and suggestions Shoppinit, always very appreciated. Fuel pressure regulator (4bars) and fuel filter have already been changed like 1 year ago when I bought the car, so these could probably be ruled out. I'll make the test without the fuel cap and report.

Regarding the OEM pumps, I've been told the main issue is their capabilities particularly with regards to E85 which puts more constraint on the whole fuel feed system. Also the aftermarket ones are reported to be more responsive than the oem's.

As far as the MAFs are concerned, i'm getting the following code: 17416/P1008 - Mass Air Flow Sensor 1/2 - Mass Air Flow Sensor 1/2: Implausible Signal.

From this http://wiki.ross-tech.com/wiki/index.php/17416/P1008, it could be either faulty MAFs (they are almost new...) or unmetered air (=air leak). Regarding a possible air leak, I've already changed all MAF seals (OEM) except those Apikol MAF seals https://goo.gl/images/r7M6WR), and also changed the air box seals. Of course the air box is a pain to fit properly but I believe (maybe wrongly) that after having done it almost a dozen of times I've become acquainted with the process. Any other routes I should explore?

I think you need to fix the MAFs before you assume there's a problem with the fuel pump.

Log the MAFs under the conditons where you get the lean mixture and let's see what story they tell.

Where did your pressure regulator come from and why did you change it?

Shoppinit wrote: ↑

Tue Mar 26, 2019 10:07 am

I think you need to fix the MAFs before you assume there's a problem with the fuel pump.

Log the MAFs under the conditons where you get the lean mixture and let's see what story they tell.

Well noted, I'll have a closer look at these fuel trim values (measurement blocks 32 & 33).

Shoppinit wrote: ↑

Tue Mar 26, 2019 10:07 am

Where did your pressure regulator come from and why did you change it?

When I bought the car I didn't get a comprehensive history of the work & maintenance that has been done on it, so I decided to do the 'first' level of maintenance for sanity reasons: oil and oil filter change, fuel filter, MAFs (Bosch BOSCH - 0 280 218 065), N75, N249, N112, spark plugs (NGK), coils, coolant sensors (just bough OEM, will be installed shortly), dump valve and this fuel pressure regulator (BOSCH - 0 280 160 575) which - from my reading- are subject when ageing to a slow decline where the pressure drops in the fuel rail little by little. The timing belt was done by the vendor shortly before selling, but probably not the thermostat, which could explain the high coolant temperature (ref the other thread viewtopic.php?f=2&t=130905&start=45).
After these changes, the car felt snappier and generally more happy compared to the first day I got it. If need be I've kept most older parts, just in case.

Shoppinit wrote: ↑

Tue Mar 26, 2019 10:07 am

I think you need to fix the MAFs before you assume there's a problem with the fuel pump.

Log the MAFs under the conditons where you get the lean mixture and let's see what story they tell.

So I finally found some time to make a few logs about what could cause the lean conditions, but before even starting I discovered the MAF readings were significantly different between Banks. To be more precise, MAF on bank 2 measures like 35% higher at idle (resp. 2.25g/s vs 3.08g/s) and this can go up to 100+% at higher loads/RPM.

First thing I did was to exchange the MAFs but unfortunately no change: Bank 2 is always higher by the same order of magnitude.

- Vaccum/Air leak? Why not but where to start? Vaccum hoses, faulty PCV or fuel tank valve? Other?
- Bad MAF connector? I guess they all are, aren't they ? On mine the rubber part is partly broken but the wires and connections look good. And if a wire were cut, I couldn't make a proper measurement, could I?
- Crappy map? I'm currently running a specific E85 map, but could a map change the MAF readings? I would say it shouldn't...

BTW, the car is idling fine, but doesn't feel as reactive as it should.

As always, any help is appreciated!

Best

You need to log the MAFs under driving conditions. The grams / second is the interesting thing. For each MAF.

Like this:

You posted while I was preparing my post.

There shouldn't be more than 10% difference between the MAF readings. Most likely is an air leak. Worst case, you've got a lazy turbo and there's an imbalance.

Having said that, your incorrect readings at idle kinda preclude a turbo problem. Most likely an air leak. I hate those airboxes.

Wow, many thanks! Turbos have been checked fine like 6 months ago when the engine was down for the transmission swap, so can we say we rule them out for the moment? So you think it's still the damned air box? Since we last discussed I've reinstalled it like 3 or 4 times..

Tomorrow I'll try to install just the MAFs without the airbox and start the engine without driving (too afraid of getting some bad stuff going into the engine). At least we'll know if the airbox is to blame..

Check the seals around the inlet too mafs, they are common for failing and drawing in air. Have a search and you'll see plenty of threads about them and replacement options. I intend too do away with maf altogether. I'm almost half tempted too go stand alone and manual just too make life easier

Thanks for the heads up! Actually I've already changed those seals, and went with the Apikol solution (blue seals). Maybe it's a false impression, but the MAFs seem properly seated.
http://www.rs6.com/showthread.php/31748 ... ls-upgrade
More to come tomorrow!

How old are your boost hoses from the intake to the turbo?

Aren't they part of the Wagner Intercoolers kit? In such case they are almost new, like 2 months old. If not, they certainly date back from 2003..

Hum, I suppose you're referring to part #30 here:

In such case I'd bet they are 16 years old or so... Wouldn't I get some signs of turbo malfunction down the line if that were the case? Or serious boost discrepancies between banks?