mechanical boost on the motorway...

[Ws2]

The problem with my s2 3b mtm chipped is, when i'm driving at normal speed on the motorway sometimes suddenly the boost is falling off to .5bar mechanical boost.

It only happend on the motorway driving the same speed

Last time i noticed a slight hesitation, like a pre warning.

When i turn off the ignition and restart the engine, the boost is back.

I changed

Knock sensors
Lambda
WGFV
DV
Cleaned the maf
no boost leaks
vacuum lines


Any ideas?

[Piu]

Mine had same problem while ago.

I noticed the knock sensor had bad contact in the harness connector. WD-40 solved the problem.

But you said the Knock sensor where replaced, right?


I also have a doubt, may the experts here can answer.
Is there any way to monitor or log the knock counting while running at boost? Vag-Com does it?

[RoadKill]

all so have this on my S2 3b as well , and its had the same replaced its all most like your over boosting and in goss in to limp mode

[Ws2]

Yes the knock sensors are new.


It always happens when driving the same normal speed and low boost. on the motorway...

[RoadKill]

mines doing it on off all the time , tonight when i turned if of the WGFV was clicking so im going to check the wirering could be a short making the wastgate open

[Ws2]

I checked the wirering but found nothing...

In limp/lowboost mode the wgfv doesn't click, after a restart it is working fine again.

[RoadKill]

im going to try and get hold of a standed ECU see what happens , mine was remaped on rollers, if not im going to look in to what power the plug to the WGFV is getting and by bass it so it still boosts not the right thing to do but there you go

[newsh]

Maybe you have a leak somewhere in the system (maybe the PCV) that makes it run really lean when off boost, the Lambda cant compensate and after a while the ecu drops into limp-home mode.

[Ws2]

that's a good one... thanks.

[Ws2]

Ok, think i found the problem.


When the car goes in limp mode, i readed out the fault codes while the engine was running, turned out it was Knock sensor #1 giving problems.
Changed the connector with knocksensor #2, and it runs great now

[s2_bo]

Maybe you have a leak somewhere in the system (maybe the PCV) that makes it run really lean when off boost, the Lambda cant compensate and after a while the ecu drops into limp-home mode.

John,

Why does a leak in the PCV system make it run lean?
Could you explain this further please.

Thanks.
Bo