Urs4 running lean . Lambda, MAF, pressurer regulator?

[UrS4boy]

That was some interesting reading! What have i been measuring then ? I mounted my gauge on the hose from fuelrail to inlet on FPR..

I can pretty well guarantee that you did not measure fuel pressure at the rail at WOT and full boost. Pump curves are a compromise combination of flow and pressure. Pumps can produce lots of pressure but very little flow or lots of flow but very little pressure. I know, based on work done by Sean D. (quattro20V), that the OE 091G fuel pump will produce around 86 psig. However, I also know from my RS2'd UrS4 that the flow capacity of the 091G is starting to be (or is) maxxed out at that pressure.

(86 psig (5.93 Bar) is critical to an RS2'd AAN because 4 bar = 58 psig and 28 psig boost (1.93 Bar) = the pump needs to supply at least 86 psig (5.93 Bar) and all the flow required by the injectors as the ECU keeps them open on a duty cycle that is likely approaching 90% at WOT).

Just for reference, an exaggerated fuel pump curve (the black line). Unless you are artificially manipulating the "boost" pressure on the FPR at idle, I think you are measuring pressure at a very low flow. I expect you will tell us something new in reply.

[Isaksa]

What now.
Does it seems like the problem is my fuelsystem ? Maybe i have to go back in the fueltank, and check hose connections then. (again)

[Val]

What's happening if in VCDS measuring blocks 001 I see lambda 1.000 whatever the rpm and other conditions are? Is lambda probe dead? No faults found. AAN engine.

Can't get boost over +0.4...+0.5bar.
N75 is checked and working, new 710n bypass, changed MAF with really working one. No leaks in intake. Could it be that WG spring is too loose? No mods have been done to it.

[prj]

What's happening if in VCDS measuring blocks 001 I see lambda 1.000 whatever the rpm and other conditions are? Is lambda probe dead? No faults found. AAN engine.

Can't get boost over +0.4...+0.5bar.
N75 is checked and working, new 710n bypass, changed MAF with really working one. No leaks in intake. Could it be that WG spring is too loose? No mods have been done to it.

Aaah the most commonly used "WG spring is too loose" excuse by people who have no idea what they are doing

NO IT IS NOT LOOSE. It is a myth. This problem does not exist.

Check your timing, might be one tooth out.

[Val]

Sorry, thanks for idea.

[Isaksa]

But how could i measure fuel delivery then?
Iv'e got 1.2liter in 15 seconds.
And to much fuel pressure...

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[UrS4boy]

But how could i measure fuel delivery then? Iv'e got 1.2liter in 15 seconds. And too much fuel pressure...

I conclude from the above that your fuel pump might be too big and powerful for this application. Sometimes there really is "overkill".

Solution could be a larger diameter, non-kinked, non-restrictive, fuel return line between the discharge side of the fuel pressure regulator and the fuel tank. In fact, the fuel return line could be whole problem: *IF* the return line is restrictive, it becomes an uncontrolled fuel pressure regulator, not allowing the vacuum-acutated fuel pressure regulator to do its thing.

C4 UrS Fuel System: From the Tank to Injectors and Back Again: http://forums.quattroworld.com/s4s6/msgs/226410.phtml

[Ugemi]

Not likely(above).
Are you sure there is no air going to the turbo inlet from anywhere else, than thrue maf(the blow of hole for example, anyway, I would check the intake pipe very carefully.)?
If everything is ok, it should run pretty much ok with the maf disconnected, little rich, but otherwise ok. I´ve done it a couple of times, when I got a boost leak and I could hardly idle with the maf connected.
If it still gets lean, it´s on the fuel side.
Have you changed the injectors? Is there´s a problem with one, this could show as a lean behavior in the exhaust. In the regular maf pipe it still gets way rich, cause the pipe size is so different and it does not show if just one cylinder is getting lean. Can you get a extra injector to test, or regular ecu software and change stock injectors and stock maf?

If it worked earlier, then it must be hardware problem and something that can get broken.

[Isaksa]

About my leak test of intake pipes.

I have made a tool to fit on the inlet on turbo, with one way valve. I can hear air is moving, but i can't tell where from. Most likley the noise is from air going through Oil retur line in turbo? But i Did not manage to build up pressure above 0.5 bar ( i had a small compressor) leakage on intake = rich mixture anyway?

The other thing i notised today when i was about to refill gas, is that i had a lot of vacuum inside fueltank. Is this normal on S4?

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[Ugemi]

If there is leakage in intake after maf and before turbo->lean, cause there is more air sucked in than measured.

There should not be any underpressure in the gastank. Leave the cap a little loose and test it.

[UrS4boy]

There should not be any underpressure in the gastank. Leave the cap a little loose and test it.

Disagree. The fuel tank is designed to run under vacuum to prevent fugative emissions of raw hydrocarbons.

N80 Evaporative Emissions Frequency Control Valve and Canister info:

http://forums.quattroworld.com/s4s6/msgs/21014.phtml

[Ugemi]

Yes, but the amount of vacuum is so small, that you wont really notice it when opening the tank. If it is that big of a a vacuum, it indicates a faulty cap(I´m not sure, but I think that it is supposed to "breathe".). Easy and free to test.

[UrS4boy]

Yes, but the amount of vacuum is so small, that you wont really notice it when opening the tank. If it is that big of a a vacuum, it indicates a faulty cap(I´m not sure, but I think that it is supposed to "breathe".). Easy and free to test.

Disagree. My car has to go through "AirCare" every two years. First test they do is they test the gas cap to see if it will hold a vacuum. If NO = fail. (It failed once, it needed a new rubber gas cap gasket). I hear air going into the tank when filling up, typically at the warning light, i.e. about 12 L left in the 80 L tank, after driving to the filling station. I think when you let the car sit for awhile the vacuum does dissipate to zero. I don't know how long that takes.

Regardless, when the engine is running, the gas cap is supposed to seal the system so raw fuel vapours from the tank are not release to the atmosphere. In that sense, the gas cap does not "breathe".

[Ugemi]

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/07/3a/0a/large/0900c15280073a0a.gif

That´s how it works. It needs to hold pressure, not vacuum. Your reason was right, it is cause it is supposed to keep the vapors inside, but when there is vacuum, it is supposed to let air it.
If it needed to be air thight, then it would be just a cap, and there would be no "moving parts". Sorry for my bad english, hope you understand, what I mean..

[UrS4boy]

http://repairguide.autozone.com/znet...5280073a0a.gif
That´s how it works. It needs to hold pressure, not vacuum. Your reason was right, it is cause it is supposed to keep the vapors inside, but when there is vacuum, it is supposed to let air it. If it needed to be air thight, then it would be just a cap, and there would be no "moving parts". Sorry for my bad english, hope you understand, what I mean..

Okay. I agree. It only breathes IN, never OUT.