Strange RPM/Boost cut GT3071 AAN S4.

[rwilthil]

Troubleshooted this for a long time, but running empty soon

This is the case.
After installation of the new turbo etc, the car ran fine. But after a few Gtech runs something happened. Just about 4800-5000 rpm the boost goes of, just like letting the throttle go. No missfire er any other signs. If i ease of the throttle and then floor it again it runs as normal up to the same rpm before boost cuts.

In the added screendump it is very easy to see that the boost drops of when the tps is still at 100% for a while before the throttle is shut.

I've also been thinking of a air leak (IC), but it seem a bit strange since it is keeping the boost for some time before dropping. In 3.rd it helds the boost about 3 sec before it start to drop.

Lowering the boost to about 1.1-1.2 bar and there is no cut.

Here is what i have tried out.
-Was running with manuel boost valve (hallmann adjustable).
-Replaced back to a new N75.
-Was running a forge diverter, now changed to an adjustable valve.
-Tried to block of the diverter, isolated totally.
-Checked the WG diaphrame.
-1,9 bar wg spring.

Other setup:
034 silicone on inlet and boost side.
Gt3071 software from 034 (26 psi).
3" Dp and RS2 Ex man.
3 bar bosch map sensor.
Full Zeitronix package.

So, a faulty MAP sensor, dodgy knock sensor?? but with regards to the map sensor i would expect a faulty reading in the instrument, but it shows almost the same as the zeitronix map sensor (26 psi ich).

Any other hint or tips??

[JP]

Not being funny but one major problem you got already is that the ECU is trying to regulate less boost than your wastegate spring which is a physical impossibility. So most likely you are getting a tremendous boost cut to safeguard your engine. Check what spring pressure the software is set for

Now the next thing is regarding the Zeitronix unit depending what map sensor you got it can only read a maximum of 25.5psi you could very well be trying to run 35+ on freespool with your wastegate spring and ECU configuration, which means it is going beyond what the ECU can read on it's stock map sensor causing a whole world of hurt.

First thing I'd do is sort the wastegate spring out to the correct one for your ECU configuration (034 should be able to help on this) then check the range of the Zeitronix unit, if necessary temporarily fit a cheap manual boost gauge to keep an eye on things.

Also if you are running stock ECU with a bleed valve leave the N75 connected to the ECU just not plumbed in otherwise the ECU starts doing funny things.

[repo]

Yea, sounds and looks heavily like safety cut, instead of a fault.

Like said above, if Your setup makes more boost than software wants, You get that particular behaviour.

Also, of course if You literally hit the 5v edge of maf signal, ecu might panic and do that.

[turbo s4]

I had a similer problem
and it turned out to be the fuelpump
greets
tom

[porkkis]

You simply hit the boost limit if no fault codes show up. Is your boost software designed for the wg spring + map sensor + frequency valve you are using? Is the WG original?
The other option is that you have hall or knock sensor fault that disables the boost control.

[blackS2]

Also, of course if You literally hit the 5v edge of maf signal, ecu might panic and do that.

We had exactly this issue at first mapping... at 6000rpm hard boost cut... reason was the maf signal range has been overrun...

[Faheemo]

Your Ecu is pulling timing cause it cant cant control boost.
You need to Get your Boost limit raised on the Ecu.
I bet you get an error saying boost limit exceeded ?
I had similar problem, and once we did that the Ecu allowed us to boost harder.

Btw on my car the MAF is maxxed out @ 3600 rpm. - she reads 5 volts therafter till redline.
The Ecu doesnt give and errors or do any thing when this occurs.

[porkkis]

The maf scale is not limited to 5 volts.

400hp equals to about 6,5 volts with std maf iirc. It's many years since the measurement was done.

[repo]

does it start from zero then?

[porkkis]

Idle equals approximately 2,5V. Can't recall if I have measured the voltage level without engine running.

[Faheemo]

yes lowest value is 2.5 volts from maf.
My bad - i didnt realise the zeitronix measures a max of 5 volts on the user input, so the maf can give well over 5v but zeitronix only sees 5v.

[rwilthil]

Im running a 3 bar bosch map sensor in the motronic, and the software/map is set to 26 psi/1,8 bar. So it should be within limits. The Zeitronics has an external map (5 bar) sensor.
The software is made for 1,9 bar wg spring. But since i was running with manual boost control i left the stock wg spring in.

There is also installed an instrument upgrade from boostinstruments (TDS-1), giving a correct boost reading even with the 3 bar mapsensor. And the reading here is moore og less equal to the zeitronix reading. They are also taken from the same outlet.

I havent checked with vagcom yet. but asume there will be some error codes (i hope..).

I was running with stock WG spring at first in conjunction with the hallmann boost controller. This worked fine for about a week. It was after the problem occoured i changed to the 1,9 bar spring and back to a N75 for boost control. But the problem remains the same.

I did have a problem with the first fuelpump, this was a brand new 005 pump. It was fine for 2 days, but then i noticed a lack of power up the boost and some missfire. Checking the zeitronix and i saw that i was running lean when passing 1,2 bar, at 1,5 the afr was up about 14:1 passing 16:1 at 1,7........ I guess i had toasted the engine if i did not had the zeitronix.... BUT there was no sign of boost cut then.
replaced the pump with a 044 unit, and all fine a short while :-)

[URSIMPO]

I had the same problem with the same turbo on my S6. I thought it was an air leak (I'd been playing with the interccoler that weekend), and it turned out to be a coilpack. So I replaced all 5 and voila!! Problem sorted!

[rwilthil]

here is a gtech run before the problem started.

[Wiell]

any diffrence when cold or hot?

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