Boost stops at 1.4bar - N75?

[Monkeymagic]

Try the WGFV in output tests on VCDS it should audibly click on and off

[hunker7]

Try the WGFV in output tests on VCDS it should audibly click on and off

...and how would I do that?

[UrS4boy]

...and how would I do that?

All you need is paper clip:

http://www.sjmautotechnik.com/trouble_shooting/ecuf20v.html#outs4

[UrS4boy]

C4 UrS Moisture Trap Info

Hi. I have a problem, my AAN won't boost past 1.4 bar (gauge), sometimes will tick to 1.5 and that's it. As before, it juddered when reaching 1.4/1.5, after I changed fuel lines, it just stops boosting, but runs without any problems otherwise. Before I had vacuum in the tank.

Ha. You've just be caught by the simplest easiest fix for lack of boost. Or at least that is what I would put my money on: The boost/vacuum hose has come off the fuel vapour ("moisture") trap on the UrS4 firewall. Re-attach small gear clamp.

http://forums.quattroworld.com/s4s6/msgs/20401.phtml

[hunker7]

Thanks guys. Checked the moisture trap hose, and i just pulled it off, changed the fastener and now it's all tight.

Should I be seeing more than .4/.5 bar in 2nd gear@6000rpm?

[UrS4boy]

G71 Manifold Absolute Pressure (MAP) sensor info

Thanks guys. Checked the moisture trap hose, and i just pulled it off, changed the fastener and now it's all tight. Should I be seeing more than .4/.5 bar in 2nd gear@6000rpm?

If you want our help, please be consistent with what you are reporting as "boost". If you are using the OE trip computer boost gauge that digitally reads out boost, that is absolute pressure, i.e. the summation of atmospheric and boost *above* atmospheric.

On that basis, your question above suggests vacuum, not boost.

Sounds like you still don't have tight tubing/hose connections between the intake manifold and the Manifold Absolute Pressure (MAP) sensor in the ECU (or the N75 really is disconnected/dead).

G71 MAP sensor info:

http://forums.quattroworld.com/s4s6/msgs/20417.phtml

[hunker7]

Sorry, i will try to be consistent from now on.

Got a day off work tomorrow, so will try to find the source of the problem.when i use measuring blocks in vagcom, i get 1000mbar reading for map at idle.

I will check the rest of the piping tomorrow and report back.

thanks

[UrS4boy]

...when i use measuring blocks in vagcom, i get 1000mbar reading for map at idle.

1000mbar = 1 Bar = 14.5 psig = slightly less than nominal atmospheric pressure.

On idle, I get about 12 inches of mercury (Hg) vacuum. 12 inch of mercury [0 °C] = 0.406 366 64 bar so I would think that a digital absolute pressure gauge would read something like 0.6 Bar at idle, not 1 Bar. You might have a faulty MAP sensor if you don't have a line leak.

[hunker7]

When I start it, it is .6 bar on the dash. In the link you gave me, it says if sensor is dead, it will show 968mbar, mine is at 1000 mbar.

[Majorcina]

I had this problem,same boost.
I belive the N75 is the problem,try to disconect it,and on conection of n75 bring 12v.When u make positive conection on N75 he shud click.If dont click its not working

[UrS4boy]

N75 WGFV info and review of N75 options

I belive the N75 is the problem,try to disconect it,and on conection of n75 bring 12v.When u make positive conection on N75 he shud click.If dont click its not working

I think you will also need to supply a ground for the N75 for this test. Apply 12V power to the male pin on the N75 that is normally connected to the female pin on the red harness wire and ground the male pin that is normally connected to the female pin on the other wire (Yellow/red on an AAN). If you get a click from the N75, that would mean the N75 is probably okay. However, it wouldn't necessarily mean that the ECU is controlling it properly. This is where the other test, via the fault code testing connections will prove that the ECU is talking to the N75 and that the N75 is responding.

http://forums.quattroworld.com/s4s6/msgs/20987.phtml

[Rusty]

Does the MTFS cut boost like it does on the ABY / ADU with the over temp alarm? If it does, then it's worth testing the MTFS by getting the car up to temp, disconnecting the plug and going for a very short run.

[Monkeymagic]

Having been through this very recently if you have VCDS plug the 2x2 leads into the OBD1 ports. Select 01 Engine and then in the right hand set of boxes select 08 output tests scroll through the various valves ISV Evap Injectors and the last one is N75 when you click slect the N75 shoould audibally click away until you click end.
If that works then it would suggest the N75 is functioning and the ECU is sending the signal.

[hunker7]

Thanks for the suggestions guys, will try them all tomorrow, and see what happens.

[UrS4boy]

Does the MTFS cut boost like it does on the ABY / ADU with the over temp alarm? If it does, then it's worth testing the MTFS by getting the car up to temp, disconnecting the plug and going for a very short run.

No. For the AAN, the MFTS only drives the coolant temp gauge, nothing to do with the ECU. The AAN ECU gets the coolant temp info from the G62 ECT sensor on the back of the head.