Boost stops at 1.4bar - N75?

[hunker7]

After adjusting the F96 I was getting 0.9 bar (1bar occasionally) , but I thought I am missing 0.1/0.2 due to timing, but now that that is sorted, it's still the same.

I am now running on my dad's N75, so yeah, I will swap that over and see if that does the job.

[newsh]

After that it's back to leak tests I guess..

[newsh]

I keep going back to the fact that this all started happening after changing the fuel lines? It's weird..

[UrS4boy]

After adjusting the F96 I was getting 0.9 bar (1bar occasionally) , but I thought I am missing 0.1/0.2 due to timing, but now that that is sorted, it's still the same. I am now running on my dad's N75, so yeah, I will swap that over and see if that does the job.

Sorry but you're still NOT getting the point.

If you only have the factory digital boost gauge which yields absolute pressures in BAR, even without an N75 connected, the waste gate spring should give you a boost under WOT of about about 1.42 Bar absolute (about 0.4 Bar (6 psig) relative boost). Any readout on your gauge less than 1.02 Bar is vacuum, no boost, just like a naturally aspirated vehicle.

[hunker7]

After that it's back to leak tests I guess..

I hope that will be the problem. I found a nice silicone hose that fits on the turbo nicely, just need to make up a plug in coming days and off we go. *Fingers crossed*

[hunker7]

Sorry but you're still NOT getting the point.

If you only have the factory digital boost gauge which yields absolute pressures in BAR, even without an N75 connected, the waste gate spring should give you a boost under WOT of about about 1.42 Bar absolute (about 0.4 Bar (6 psig) relative boost). Any readout on your gauge less than 1.02 Bar is vacuum, no boost, just like a naturally aspirated vehicle.

With N75 disconnected, it shows 0.5 gauge pressure (1.5 absolute)

[newsh]

Boost stops at 1.4bar - N75?

Sorry but you're still NOT getting the point.



If you only have the factory digital boost gauge which yields absolute pressures in BAR, even without an N75 connected, the waste gate spring should give you a boost under WOT of about about 1.42 Bar absolute (about 0.4 Bar (6 psig) relative boost). Any readout on your gauge less than 1.02 Bar is vacuum, no boost, just like a naturally aspirated vehicle.

Dave, he's seeing 1.8 bar on his dash and converting that to 0.8 bar of boost by subtracting the 1 Bar atmospheric pressure. We're talking about "Boost" not "Absolute Pressure".

[UrS4boy]

Dave, he's seeing 1.8 bar on his dash and converting that to 0.8 bar of boost by subtracting the 1 Bar atmospheric pressure. We're talking about "Boost" not "Absolute Pressure".

That makes me crazy. Easier to just tell us what the digital gauge is reading.

[geneandbolly]

( i know...i don't have a bloomin' clue what they're on about either!!)

[UrS4boy]

One final suggestion before I fly over to Blighty to scope out Art Deco buildings in London, etc.

From jretal on my home forum:

"he check to see if the cats were clogged? when in doubt and nothing else is found to be wrong, loosen the flange before the cats and remove the donuts and see if you have boost again. "

Good luck. I trust it will all be sorted when I get back.

[newsh]

I know but then all the S2 boys with Vacuum-0-Boost type gauges start saying things like.. "1.8bar is too much, you should only be getting 1.3!"

[hunker7]

What i do find weird is that fuel pump will run occasionally when car isn't running, as in getting the pressure up in the system.

I tried starting the car today, it sort of starts but wasnt picking up the revs.

I did swap fuel pump from my A100 into an S4..could they be different?

[Vorsprung durch Technik]

Easier to just tell us what the digital gauge is reading.

And that was my post a couple days ago but the suggestion just vaporized into thin air Why not use "absolute" pressure of the cars digital gauge instead? Would make life easier for lesser mortals and no more confusion.

Janis, changing the fuel pump to the 2.6 pump has surely got to be a negative?

[S2central.net]

I've not read all this thread, but I suggest all the fundamentals are checked - along the lines of -

- Mechanical timing... double check the timing marks and be certain the sprockets aren't skewed off (damaged keys)
- Does this AAN engine have the G40 camshaft sensor in the dissy housing - if so check it is aligned too
- Check that G4 and G40 signals are aligned properly (needs oscilloscope) - G4 must appear in middle of the G40 window
- Don't mess around with F96
- Get a proper boost leak test
- Use only known good fuel pump - must be 3B/AAN/ABY/ADU spec pump as a minimum - not any old Audi 100 pump
- Check you are getting full throttle when you mash the loud pedal - measure/check volts at the throttle pot
- Are you clearing fault codes to ensure the ECU isn't holding a fault which disables active boost control (N75 disabled) ?

Also - if you are using the UrS4 boost gauge as your reference point then keep quoting its results on the same ABSOLUTE scale or we will go a bit bonkers.

[hunker7]

Thanks for the suggestions S2 central.

AAH,AAN,ABC run the same fuel pump, so that can't be the problem.
Timing is now good, but I will take it all apart on Sunday and do it up from ground up.

I don't understand what you mean by G40 and G4. G40 is behind cam sprocket, and G4 is by the gearbox?