URS6 Way Too weak!!!

[HMS-S6]

Over two years ago?

Measure it now?

I'm by no means against re-checking my checks so i will check it again under load when the rain clears! I DID check this under full throttle to 6000-ish rpm in 3rd 4th and 5th two years ago and since then the fault hasn't changed at all, i've been chasing this on and off for 5 years now. Getting proper time on it inbetween customers cars is quite difficult atm.

[UrS4boy]

I agree with twoqu and pri on the fuel supply issue in that it needs to be checked. The fuel pressure at the rail needs to be 4 Bar plus the boost pressure, e.g. at 24 psi boost, the fuel rail needs to be 58 + 24 = 82 psig or 5.66 Bar. Any less and the injectors won't be able to supply the fuel required by the ECU.

As for flow, I noticed the other day that the fuel line that Audi replaced because of a recall in North America in the late 1990's has a rather kinky 90 deg bend right at the firewall which would happer both fuel delivery AND pressure. This *could* be overcome by the installation of a 044 Bosch Motorsport fuel pump (which *is* on my list of things to do). In the short run, relaying the FP to the battery can boost output:

These may or may not help:

General UrS4/S6 fuel pump info includng flow testing (note the various embedded hyperlinks): http://forums.quattroworld.com/s4s6/msgs/22623.phtml

Relay DIY: http://forums.quattroworld.com/s4s6/msgs/24327.phtml

[prj]

That's exactly my point. That's why I said to measure fuel pressure under load.

[twoqu]

It does seem that the issue is something on the car, if we accept that there are no boost leaks and no fault codes. Would have thought that a sensor or wiring issue would have flagged something up to give us a clue.
I am reminded of a Ur that had a fuel delivery problem. After changing the regulator, filter and pump for an upgraded one it was little better. The only remaining suspect component being the fuel tank itself. How could that be an issue!
Sourced another tank, poured some fuel into and it poured out. Done the same with the original and it trickled out! The problem was a big blob of weld where the outlet pipe had ben welded to the tank internally.
Obviously the S6 does not have such a tank but I was wondering whether there is a fuel volume rather than a fuel pressure problem. So another thing to eliminate are the actual fuel pipes on the supply side. Perhaps it has been squashed somewhere and is restricting flow. It does not explain how the symptoms would have got worse over the years though, unless the pump's performance was adequate to overcome it initially and has subsequently struggled to supply the necessary volume.
So basically I am suggesting a thorough investigation of the fuel lines!

[prj]

Over two years ago?

Measure it now?

[HMS-S6]

And what were the numbers? What did you see there during 1 bar of boost?

The problem is, the way you come across is you are saying you checked everything and are very sure of everything. Well, I on other hand am sure you missed something, which you just assume is OK and dismiss it. If everything was really OK, your car would run properly as well.

Can't remember off hand what the numbers were as it is something i checked over two years ago but remember it was identical to my well running S6 saloon.

I am very sure of what i have checked as i have been a mechanic for many years, however there are MANY thigs i have not checked at the other end of the loom so to speak, which is why i'm susspecting a fault in the wiring, but now my 'control' car has been scrapped i have no reference point. This is the only car i have EVER failed to cure.

[prj]

Done that. Ran my snap-on gauge round the bonnet on safety catch and under wiper so i could see it while driving.

And what were the numbers? What did you see there during 1 bar of boost?

The problem is, the way you come across is you are saying you checked everything and are very sure of everything. Well, I on other hand am sure you missed something, which you just assume is OK and dismiss it. If everything was really OK, your car would run properly as well.

[HMS-S6]

I mean fuel pressure under acceleration.

Done that. Ran my snap-on gauge round the bonnet on safety catch and under wiper so i could see it while driving.

[prj]

I meant measure the values, which i think you knew full well!!!

Measure pressure under acceleration? As in boost pressure with a mechanical gauge, if so then i've done that and all is the same as my 'controll' car i then scrapped and now regret!!

Compressions when i checked after fitting the head were within 1-2 psi of eachother and all correct.

I mean fuel pressure under acceleration.

[HMS-S6]

MAF map huh what?

Measure pressure under acceleration.
Measure compression in all cylinders.

I meant measure the values, which i think you knew full well!!!

Measure pressure under acceleration? As in boost pressure with a mechanical gauge, if so then i've done that and all is the same as my 'controll' car i then scrapped and now regret!!

Compressions when i checked after fitting the head were within 1-2 psi of eachother and all correct.

[prj]

MAF map huh what?

Measure pressure under acceleration.
Measure compression in all cylinders.

[HMS-S6]

Okay well, Motronic is pretty damn simple when it comes to putting fuel in.
If there is nothing mechanically wrong with the thing then it's as simple as dividing the MAF value by RPM. Then some maps and that's it.
Of course this is assuming that the fuel pressure is alright.

So - you pressure tested everything, let's assume there are no leaks.
Now test the fuel pressure, make sure it is not tapering off. The fuel filter might be clogged or the fuel pickup.

I'll look at the MAF map as the FPR is new, as is the pump anf filter, all audi parts and the fuel pressure, last time i checked it was bang on spec! Thanks for the help so far!

[prj]

Okay well, Motronic is pretty damn simple when it comes to putting fuel in.
If there is nothing mechanically wrong with the thing then it's as simple as dividing the MAF value by RPM. Then some maps and that's it.
Of course this is assuming that the fuel pressure is alright.

So - you pressure tested everything, let's assume there are no leaks.
Now test the fuel pressure, make sure it is not tapering off. The fuel filter might be clogged or the fuel pickup.

[HMS-S6]

Crank and cam sensors are never going to cause this.

Try disconnecting the O2 sensor and then driving. There are two connectors - one for power, and a single pin one for the signal.
You had a "signal too low" code before, if that is continuing to happen, it might be the culprit.

O2 sensor is brand new Audi and have driven with disconnected and makes no difference, which is no real surprise since you told me in a previous post that the signal is not used under full throttle. I had no 'signal too low code' it was the live date from the vag-com i was refering to.

[prj]

Crank and cam sensors are never going to cause this.

Try disconnecting the O2 sensor and then driving. There are two connectors - one for power, and a single pin one for the signal.
You had a "signal too low" code before, if that is continuing to happen, it might be the culprit.