What else cause 0.4-0.5 bar max boost

[shone190]

I have problem with max boost on AAN engine, so I was wondering what else could limit max boost to 0.4-0.5 bar?

1. N75
2. MAF
3. Boost leak on some hose/s
4. TPS
5. ...

[Jamo]

Or the fuse to the N75 valve, if your running 0.4 bar your running wastegate spring boost, boost leak would give you violent kangarooing from the boost cut on the ecu.

TPS is a good one use vagcom to make sure you are seeing WOT wide open throttle.

[UrS4boy]

Hose off at the moisture trap = ECU doesn't get boost signal, doesn't control N75 = mechanical boost only. Check your hoses. If they are tight, it is the N75. Perhaps it is unplugged

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

[shone190]

Until now, I tried to change N75 for one from S2 which is brand new and is working, but boost is also 0.4 bar, so I eliminate this. I think that on my car there is no moisture trap, only the hose straight to the ECU. I also check the fuse and PIN 1 (with LED) on N75 connector, and LED is on when I turn the ignition.

So, I need to check TPS with Vagcom or with multimeter?

What else could I do?

[UrS4boy]

I think that on my car there is no moisture trap, only the hose straight to the ECU. What else could I do?

Check to make sure that the hose from the intake manifold to the ECU has no breaks in it and is securely fastened to the ECU at the brass tube that connects to the MAP sensor (the black box in the photo, via the rubber hose in the ECU):

ECU closed showing the brass tube in the lower right corner.


ECU open showing the brass tube and hose it connects the intake pressure/vacuum to the Manifold Absolute Pressure (MAP) sensor:

[shone190]

OK, I'll check it too.

[rs200]

TPS must give 1800ohm on WOT.. if I remember well. mesured it betwen 1. and 5. pin with multimeter
In one case (on Zoran's 200 20v from Šabac) it have faulty MAP sensor , and than I get 0.4bar , we change ECU and than everything was fine..

[shone190]

Thanks, I'll check TPS, but is there any method to check MAP?

[rs200]

yes.. do you have "bar" on board computer ? there must be the same value like on your Boost gauge..
if your car now go until 0.4bar , on board computer they will show you 1.4bar
if the value not the same .. MAP is problem..

but one more thing.. "bar" on dash can have delay of 1-2 second , so this is normal..
I don't thing that you have problem with MAP..
check your Blow off valve.. they have a leak . I'm sure 98 %

[shone190]

Yes, I have boost gauge on UR digital dash, but I didn't look there



I hope that gauge works and I'll check it today and compare with other boos gauge.

How can I check blow off valve?

[javispa]

My 3B was running at this bar pressure and it was because the dizzy was set a bit out of its point. The car fired but the boost was limited to 0,4 bar (if the dizzy is set even worse, the car doesn't fire). A fault code appeared on VAG Com relating to hall sender.
I know your car is not a 3B, but probably a faulty signal from the hall sender may have the same effect on your car. If your AAN engine is the earlier one, you may have the problem I had on my 3B. Setting the dizzy to its point, and after checking there was no fault code, solved the problem. You could try the same with the "tuna can", supposing it is wrongly set.
I have also experienced the same boost problem with a ECU that gives a fault code, but I don't know which one or why. The car fires but with no boost. It is only a problem I have with this particular ECU.
Also a friend of mine was having the same problem and, in his case, it was caused by a faulty wastegate. By the way, how is your turbo?
I would check the faulty codes. It may not solve the problem but it will give you a clue to know which one it is.
Cheers.

[max_s2]

Faulty knock sensors(s) also can cause not boosting over 0.5bar. Had a bad connection once under the hood. Mostly this is caused by a faulty N75 valve.

[rs200]

would not faulty knock sensor or bad signal on them give a fault code ?
I think it will.

blow off have 3 inlet , 2 big and 1 small .. this small gate go on inlet manifold , disconect them and try with your mouth hold the vacum.. them must hold the vacum . if they don't , they are broken..
prepare 35 euro for new one..

I drive 2 years my 200 20v , and I could not find the problem why they go only 0.5 bar..
the problem was in small leak in blow off

[shone190]

Great info, I'll have what to do today, after job

[S2central.net]

AFAIK - the only knock sensor faults that raise codes are if it is unplugged or shorted out.... If the ECU gets a rubbish signal or no signal from knock sensor then it doesnt raise a fault...