AFN running issues

[jc_geddes]

Evening all,

My AFN converted van has a running issue, I left it at my parents house over winter and went to move it last weekend.

It started fine and initially drove okay as well, but it started to not always create boost, some time you had it other times not, staying in gear and actuating the throttle pedal from 0 - 100% would some times bring it back - so what could it be?

Vacuum leak - engine side of the N75 valve - previous experience says this leads to no boost all the time (not the cause)
Vacuum leak - turbo side of the N75 valve - not had previous experience but would have said as above either you have enough or not, (not the cause)
Sticky TC vanes - can't rule this out yet - didn't have good access and found it difficult to actuate the rod with the access I did have - but this to me would lead to either boost or no boost not intermittent boost?? (Not the cause)
Blocked air path - Air filter side (mouse nest??) not sure this would lead to the intermittent nature (not the cause)
Blocked air path - exhaust side as above?? (I have heard about cats which have broken up and caused issues like this - but I have no cat in the system)
Dodgy N75 valve? Possibly but it was replaced about 1 year ago.

The bit that gets me is the intermittent element, and this can be within a gear and feel like you are pumping the accelerator, I've full load no load full load .... When all you have do is keep it at 100%

Going back to have a better look with VCDS with me and a vacuum gauge, but it's 100 miles away and I need to take everything I need so have I missed a possible issue and what are your thoughts on the above - have I dismissed anything which you wouldn't?

Any views appreciated

John

[davegsm82]

Hi John,

While it may feel like its boost related it's not necessarily always the case, it could well be something like air leakage into the fuel line although there will usually be a max-deviation error in the ECU relating to the pump maxing out. Easy to dismiss with some pipes and a container of diesel for a test run.

On the Vac side of things, I've found many instances of failed boost actuators, they get holes in the diaphragm from rust flakes floating about inside. Test it using a mityvac, big syringe or even just your mouth on a clean pipe attached to the vacuum connector. pull a vacuum on it, it shouldn't leak away, if it does then it's knackered.

Dave.