S6 timing

[UrS4boy]

Is 0.2 bar low on fuel pressure enough to cause a problem?

The ECU assumes that there is 4 Bar of pressure available across the injector(s) when it selects what it thinks is the appropriate injector duty cycle (i.e. the period of time that the injectors are cycled open) for the given situation, e.g. RPM and load. As I understand it, when the car is NOT at WOT, there is feed back from the O2 lambda sensor that the ECU will use to adjust (increase in this case) the duty cycle to correct the lack of fuel that less than 4 Bar across the injector would cause. However, there are limitations on that adjustment capability. At WOT, the O2 sensor signal is ignored by the ECU so adjustments are NOT possible.

prj will correct me where I am wrong.

[HMS-S6]

That's my thought process too Dave and I have to say that although it varies slightly it sits about 13.5-13.8 at WOT around 3,500-4,000 RPM. maybe the 0.2 bar lack of fuel pressure is enough???
A friend is breaking a 96/7 S6 avant and I'm thinking of putting the complete tank pipes and everything into mine.

[twoqu]

Have you got anything teed into that fpr pipe?

[HMS-S6]

I just thought the lack of adjustment either way may be lines to the FPR but I've checked checked and checked them again. May try them with a hand vacuum/pressure pump to be sure before delving into the tank which quite typically is now as full as full can be!!!!

[HMS-S6]

No. Nothing is tee'd in. My boost gauge us off the one to the heating?

[HMS-S6]

Calling PRJ. haha.

[twoqu]

It would be useful to know (if we are discounting unmetered air) how much fuel would be needed to put the afr back to an acceptable level. Desen't sound a great deal at 0.2bar even taking into account gauge accuracy.
What could be wrong in the tank? If not an actual physical problem such as the pump has come out of the basket or the basket is not secured in the tank or something!

[HMS-S6]

I have an adjustable FPR of high quality. Could try it tomorrow.

[HMS-S6]

It would be useful to know (if we are discounting unmetered air) how much fuel would be needed to put the afr back to an acceptable level. Desen't sound a great deal at 0.2bar even taking into account gauge accuracy.
What could be wrong in the tank? If not an actual physical problem such as the pump has come out of the basket or the basket is not secured in the tank or something!

I was thinking maybe split in a hose (not feed) introducing air or something? Or despite what it looks like the basket filter being blocked?

[prj]

At 1.5 bar, if you have 4.9 bar fuel pressure instead of 5.5 bar, then this is 0.6 bar difference.

To see how much difference this makes to the AFR, you would need to do the following calculation:
sqrt(5.5/4.9), which comes out as ~1.06, so 6%.

If you have 13.2 AFR, then a 6% richer mix would yield 13.2/1.06 = 12.45 AFR.

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With the stock software, if we have 4.8 instead of 5, that is a difference of sqrt(5/4.8) or 2%.
If you take in account 13.2 AFR, then it would be 12.9 with the correct pressure.

To me it sounds like you have a fuel delivery problem with the fuel pressure tapering off on top.

[UrS4boy]

No. Nothing is tee'd in. My boost gauge us off the one to the heating?

If true, bad idea. Good idea is to "T" in a boost gauge signal hose between the AAN intake manifold and the moisture trap (which is on the UrS4 firewall and for the UrS6, it is down by the ECU (plastic can with two hoses in/out).

[HMS-S6]

At 1.5 bar, if you have 4.9 bar fuel pressure instead of 5.5 bar, then this is 0.6 bar difference.

To see how much difference this makes to the AFR, you would need to do the following calculation:
sqrt(5.5/4.9), which comes out as ~1.06, so 6%.

If you have 13.2 AFR, then a 6% richer mix would yield 13.2/1.06 = 12.45 AFR.

----

With the stock software, if we have 4.8 instead of 5, that is a difference of sqrt(5/4.8) or 2%.
If you take in account 13.2 AFR, then it would be 12.9 with the correct pressure.

To me it sounds like you have a fuel delivery problem with the fuel pressure tapering off on top.

S**t me you're a clever guy. Thank you!

Is the dash readout always a little slower to display than the mechanical?

[HMS-S6]

If true, bad idea. Good idea is to "T" in a boost gauge signal hose between the AAN intake manifold and the moisture trap (which is on the UrS4 firewall and for the UrS6, it is down by the ECU (plastic can with two hoses in/out).

Right ok, I can change that easily tomorrow. Why is it being off that other one a bad idea Dave?

[twoqu]

Thats encouraging!
Are you 100% sure that there are no electrical issues particularly with charging. Seems to me the pump struggles at higher rpm which is consistant with the voltage dropping. I think I mentioned before it seemed to be @0.5V down!

[HMS-S6]

Thank you but yes I've had a lovely feed to the pump plug itself since the relay job thing.