What else cause 0.4-0.5 bar max boost

[blackS2]

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

this is the most common failure on AAN engines for limp mode but you will see allways 1,0 bar on OEM boost gauge in this case in all driving conditions

[shone190]

I hope that something You mentioned in this thread is my problem

Howewer, I'll check a few things after work, so we'll see... ))

[UrS4boy]

this is the most common failure on AAN engines for limp mode but you will see allways 1,0 bar on OEM boost gauge in this case in all driving conditions

True but only *IF* he has a OE in-dash trip computer/digital absolute pressure boost gauge. If he has an aftermarket analogue relative boost boost gauge, then he will see the 6 psi (0.4 bar) mechanical boost of the stock waste gate spring. Something is preventing the ECU from controlling the waste gate.

BTW, losing the boost signal connection at the UrS4 moisture trap does NOT put the ECU into "limp" mode. It just doesn't produce more boost than 0.4 bar. Other than that, it drives normally. Not a "limp" situation.

[shone190]

Now I have one URS4 with AAN engine (which is ok and have 1 bar boost), I tried to swap some things and find the problem on my UR with AAN and nothing solved yet

1. N75 from URS4
2. Dump valve from URS4
3. Complete ECU from URS4
4. MAF
5. Changed all vacuum hoses with brand new
6. Moisture trap from URS4
7. New turbo hose from Maf to turbo


What else I can try?

TPS
Boost leak test
...

I doubt that boost leak is the problem, so just be exactly 0.4 bar as mechanical boost.

Is there any ideas what else to check, as I have one spare car which is completely stock and working

[newsh]

Mfts?

[shone190]

Mfts doesn't control boost on AAN, just on 3B.

[newsh]

Ah sorry, in that case temp sender on back of cyl head maybe?

[Knight Rider S4]

HAve you plugged the car into vag.com ?

Output check on the engine and make sure everything working as it should

post up fault codes

[shone190]

Problem is still here and this is a list what I tried to change:

1. N75
2. Dump valve
3. ECU
4. MAF
5. Changed all vacuum hoses with brand new
6. Moisture trap
7. New turbo hose from Maf to turbo
8. TPS

What else I can try?

As I see on forum, only thing I didn't try is boost leak test, but it's a little weird that it's a problem, because boost is exactly 0.4b, just like mechanical boost

[UrS4boy]

Problem is still here. What else I can try?

Your ECU is NOT either NOT talking to the WGFV OR there is no boost signal going from the intake manifold to the MAP sensor in the ECU.

Not sure how much of the AAN engine harness you used but if it was all or most, you can check the communication between the ECU and the devices it controls, e.g. injectors and WGFV, by stimulating the ECU to do a test, as outlined at SJM Autotechnik:

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

[shone190]

I tried this test but it doesn't work, I don't know why

[UrS4boy]

I tried this test but it doesn't work, I don't know why

None of it or just the WGFV portion? If the ECU isn't communicating with the devices it was designed to control during a test, then there is no way it is going to make them work like you expect it should during actual engine operation.

How much of the AAN harness did you use?

Link to the AAN ECU T55 pin-out:

http://forums.quattroworld.com/s4s6/msgs/21009.phtml

[shone190]

None of it doesn't work, not just WGFV test. I didn't do engine swap, my friend did but everything was OK until few months ago.

Is there any way to determine if there is ECU-WGFV communication during the driving?

On my ex Audi S2, test worked ok until I chipped ECU. After that, test didn't work, but everything was OK with boost, 1b on WOT. My URquattro is chipped also, but I didn't try to test it with stock ECU I have, maybe I should try that too

[Jamo]

Have you checked the fuse? and you should be able to do an output test in vagcom, should hear the n75 click working on that test IIRC

[Avantus]

A friends RS2 had 0.4bar boost due to a faulty MFTS. Unplugging it made it boost back again.