3B boost problem (again...)

[max_s2]

Hello guys.

I know there are 1000+ boost problem topics, but I think this one will differ from others.

Here are some good facts about my friends car:
1) No faults in ECU
2) No boos leaks at all. Tested every single vac line - all in good condition, holding boost.
3) Fuel pressure and flow - OK!
4) WG diaphr. - OK!
5) No cats etc, only stock end.
6) Done output tests - everything clicks and seems to work fine.
7) Not running rich or lean, consumption OK!

..and here comes the bad/strange ones:
1) Boost not going above 0.6bar. It jumps up to 0.6bar and then drops down to 0.5bar (sometimes 0.4bar (relative)). With unplugged N75->WG vac line, we can get 1.3+ bar and then comes the fuel cut in. We pluged special vac/boost tool to WG's upper camber and pressurised it by +0.3-0.5bar (this basicly means we help WG to be closed) - then we got aprox 1bar on the gauge. Could this mean something.. or not?
2) Tacho sometimes jumps 500-2000rpm above current RPMS. What could cause this? And could it limit boost?

We have spent so much hours testing and working on the car that we are really fed up.. so I decided to put my pain in here

[dkw_dude]

I'll try some suggestions:
Try a fresh/new n75. Clicking is a good sign, but it could still be disfunctional. Also the MFTS (the big 4 pin temperature sender) under the water manifold can disable n75 operation if engine is too hot, or the temperature sender itself is faulty. Easy to check, just pull off the connector and go for a test drive.
The tacho jump thing sounds strange??

[lind4hl]

[max_s2]

N75 has been swaped from my S2. That is working and must be OK! Ok, today will try to disconnect those two temp. senders

[max_s2]

So tested the car, but no differences.
We got this:
2nd gear - 0.5bar
3rd gear - 0.6bar
4th ear - 0.75bar
..and as it receives 3500rpm, drops down to 0.4-0.5bar

[max_s2]

So.. found one fault - DV was put in in oposite way.. we put it back as it must be but still nothing. Only when idling it now has -0.5bar vac (before was -0.7bar).
We screwed in the WG screw, also screwed it out but nothing changes - still got only 0.6bar for a little bit and then dropdown to 0.5bar. When unplugging N75->WG vac tube, it goes up to 1+bar and then cuts cuel.
I will upload some videos shortly.

[max_s2]

2nd gear:

http://www.youtube.com/watch?v=sEEDZs44v4Q

3rd gear:

http://www.youtube.com/watch?v=i27b9IToGhU

4th gear:

http://www.youtube.com/watch?v=cdatx-YFbGE

[Tonks4x4]

To be honest that looks about right for a non chipped 3B....

Get it remapped......

[max_s2]

You think so? Pressure starts to drop after revs hits aprox 3500rpm, my ex-S2 had stable 0.8bar till ~6500rpm IIRC.

[max_s2]

Oh forgot another thing. We changed ECU to an chipped one, still the same - 0.6bar max. Only feels a bit stronger duo to fuel map changes etc.

[max_s2]

Damn.. we screw in/out, but nothing changes.. I dont understand where can be the problem

The tension in the wastegate spring can also be fine tuned by adjusting the upper perch in the top of the wastegate chamber. In doing so, this can increase the amount of pressure required to crack open the wastegate and so provide a cheap and easy way of increasing boost. However - the
practise is NOT recommended as the ECU may detect an excessive boost condition and go into 'limp-home' mode.

[newsh]

Exhaust blocked?

[Tonks4x4]

If a chipped ecu has no effect. Then it has to be either n75 or the wiring to it

by using another ecu you have also ruled out a faulty map sensor.

If you can produce 1.3 bar without the vac line to the wastegate then the spring in the wastegate must be strong enough.

[max_s2]

Exhaust - OK!
Wiring to N75 checked - OK!
With the upgraded ECU we had 1.5bar on gauge (with disconnected WG->N75) - should be OK!
Tryed 3 ECU's total - all have the same issue.

[Tonks4x4]

Did you try disconecting the MFTS?