Mfts -how much does it affect boost ?

[newsh]

A bad (or loose) knock sensor can cause a reduction in boost and not show a code.

Atmospheric pressure sensor can do the same.

[prj]

The AAN loom doesn't carry the signal from MFTS-R pin to the ECU... The AAN software running in your ECU should not be interested in this pin, but if that same ECU runs ABY or ADU software then the R-pin comes into play (as long as you have ABY/ADU loom).

1) All ECU's have the same logic. On AAN there's just no wire. If you ground the pin on AAN ecu it drops boost to spring pressure just the same.
2) Knock sensor fault does not just reduce boost, it drops it to spring pressure.
3) MFTS fault does not just reduce boost, it drops it to spring pressure.

In fact there is not a single fault with the ECU that will reduce boost by any really noticeable amount.
You either have boost or you have spring boost, there's no real in-between.

In all other cases where your boost is low, either target is not what you think it is in the software (you don't know your software or your TPS is not hitting at least 87 opening, or altitude sensor shot - two latter diagnosable with VCDS), or the N75 is already at 99% and you have a hardware fault. The boost controller is very aggressive, if it cant reach target it WILL drive the N75 to 99% VERY quickly.

[S2central.net]

That's cool - I didn't know the aan code had the R-pin logic. Agreed completely above that those faults (and others) when detected just disable active boost control so it drops back to spring pressure.

[UrS4boy]

1) All ECU's have the same logic. On AAN there's just no wire. If you ground the pin on AAN ecu it drops boost to spring pressure just the same.

Hmm...the way I read that, you have just described how to add a pin to the T55 ECU connector at position 46, run a wire from that pin to a hidden switch and run a wire from the other side of the switch to ground to create a "Valet" mode, i.e. only spring pressure so the parking jockey can't have too much fun with your C4 UrS.

No?

[S2central.net]

You would be the man to prove the theory Dave. Does seem odd that AAN code will work when they didn't wire it up but if prj says the code is there then who are we to dispute it !!!!

[S2central.net]

As for valet parking I would say over my dead body, but let's call it "spouse mode" ;-)

[prj]

Hmm...the way I read that, you have just described how to add a pin to the T55 ECU connector at position 46, run a wire from that pin to a hidden switch and run a wire from the other side of the switch to ground to create a "Valet" mode, i.e. only spring pressure so the parking jockey can't have too much fun with your C4 UrS.

No?

Sure, it will work and leave no fault codes.