2002 D5 Pulsing turbo boost at high RPM

[purplemk]

Hello everyone
I have been reading through the threads regards turbo issues but as yet haven’t found anything that quite matches the problem I'm having.
V70 D5 2002
Engine revs fine up to about 2500 RPM but at about 3000 the turbo vacuum actuator starts pulsing on and off / full movement constantly, the hoses to the intercooler can be seen to bulge and release every couple of seconds.
The engine revs don’t alter much but the boost pressure is on and off constantly
When driving underload / accelerating hard at that point it will drop into limp mode and restrict revs to 2500 RPM
I have checked for vacuum leaks / hoses / actuator / VNT movement all ok

my question is what controls the boost actuator / boost pressure?
As far as I can tell the "boost control solenoid" at the front of the engine is simply a open or closed valve, closed at idle open at revs, but what controls the amount of movement on the turbo actuator / boost pressure?
or has anyone had this symptom before?

I have a Icarsoft pro but for some reason I can't read the ECU fault codes just get "link error" although I can read the live data such as boost pressure / actuator % etc etc
Any ideas much appreciated

[ca2n]

Since you can monitor boost pressure, perhaps note what the max value is when it is cut off? It could be the computer protecting the engine from an overboost situation. From memory, maximum boost is around 31 psi.

The solenoid/valve near the air filter box regulates when vacuum is supplied to the engine pads. It regulates this with engine speed and is pulse-width modulated.

The other solenoid/valve near the starter motor is what controls the VNT operation, depending on several parameters including, but not limited to, engine coolant temperature, engine load, throttle position, engine speed, etc.

[purplemk]

Originally Posted by ca2n

Since you can monitor boost pressure, perhaps note what the max value is when it is cut off? It could be the computer protecting the engine from an overboost situation. From memory, maximum boost is around 31 psi.

The solenoid/valve near the air filter box regulates when vacuum is supplied to the engine pads. It regulates this with engine speed and is pulse-width modulated.

The other solenoid/valve near the starter motor is what controls the VNT operation, depending on several parameters including, but not limited to, engine coolant temperature, engine load, throttle position, engine speed, etc.

Thanks for the reply. I think you may be right about it cutting out to protect the engine, its difficult to be sure but it seemed to over boosting judging by the way the intercooler hoses expanded and contracted, I haven’t managed to record any actual figures when its pulsing but during normal driving i got 17 psi max.
unfortunately the instrument cluster is also failing intermittently so I wonder if that could possibly be upsetting the ECU?

[ca2n]

The intercooler hose that runs underneath the engine does expand with boost; I wouldn't find that unusual.

My guess is the 17 psi that you have read is the gauge pressure, which combined with atmospheric pressure (14.7 psi) gives a total pressure of 31.7 psi, which is still within limit. Although the design maximum pressure is around that value, I am not sure how much overboost (3 psi, 5 psi, 10 psi?) is allowed until a code is triggered. It would still be interesting if you can get a max value of the boost when the code is triggered. I too have it on my D5 but have just got used to it; it's probably sticky vanes on my turbo which is not a priority for me at the moment to get sorted!

Failing of the instrument cluster (DIM) is not uncommon among the P2 models. There are services you can get to get them fixed.

Hope this helps.

[Mike A]

I assume you have checked vacuum on front and back engine mounts....I had same problem changed the tcv behind the starter mounted on engine block ....cured .
Note be careful around starter live contacts either disconnect battery or cover with rubber mat ..trust this is of some help