WTF golf mk4 overboost

[mrapoc]

So I have tried everything so far to sort my overboost.



Thats what I get from a WOT.

What could be causing it?

Some interesting notes:
Adjusting the actuator seems to have pretty much no effect on overboost even when lengthened as much as possible
VNT was sticking end of last year - I had it cleaned and actuator replaced at same time
VNT doesn't seem to be sticking at all and actuator holds vacuum
Changed the MAF last year from non-genuine to genuine
Changed the MAP just for giggles
Cleaned the intake manifold
Blanked off the EGR
Decatted
Tried two new N75 valves as I broke the original, and took the new one back under warranty as I thought it was causing this
Vacuum pipework replaced and simplified so that it only applies vacuum to the n75
Does the same regardless of Map or Remapped

Do I need to check fuelling (if so how?)

Hopefully you guys have some thoughts on the matter

Many thanks

[chittychittybangbang]

This isn't a PD engine right? If not, you can use vag-com / VCDS to see air injection quantity which means fuel inject quant

Can't just adjust the rod, use vac pump to adjust rod to correct length and let ECU and N75 solenoid regulate the rest.

Is it possible that the VNT is sticking again?

[mrapoc]

Hello

Sorry it is a 115 AJM so it is a PD engine.

I didn't adjust the rod in the first place, a garage I took it to lengthened the actuator to try and compensate for the overboost. At this point I didn't know it was overboosting.

After talking to the guys who did my VNT clean, they assured me it was correctly boosting when it left their premises and that the actuator should not have been touched.

So I tried setting it near enough back to the factory recommended (using a vacuum gun) but it makes no difference to the overboost.

The actuator moves smoothly down to the stop screw but not totally smooth on the way up, nethertheless it still returns to the top in decent time. I can also move the VNT arm down myself by giving it a push. I haven't removed the actuator yet for a proper wiggle test as it seems a pain

Thanks

[mrapoc]

Think the plan of action is

Boost leak smoke test

Remove actuator and test VNT lever moves fully

Secure VNT arm to minimum boost position

If it still overboosts then the vnt control is either not working at all or there is something causing it to be ignored such as too much exhaust flow or overfuel?

[chittychittybangbang]

You can never have too much exhaust flow. Overfuel is rare and not nearly as common as vnt control issues. Unless you're chipped or modded, why would it overfuel?

[mrapoc]

Ok. Injector failure?

Anyway, it does exactly the same regardless of mapped or not (I've tried both).

If its "ok" (boost is still erratic but not massive) at driving unless I WOT (3rd gear, pedal to the metal - thats when i limp mode) what could that be an indication of? Weak actuator?

[chittychittybangbang]

Maybe, test the actuator http://www.myturbodiesel.com/1000q/a...ate-adjust.htm