V70 Tdi - cleaning airways advisable ?

I have a 1997 V70 TDi 2.5 litre, 165,000 miles, and am getting hesitation
around 2500 rpm - is it some sensor in the airways needing cleaning and if
so, how to clean ? - I have heard there is some air mass sensor that can get
dirty with age and messes things up and a fine hot wire benefits from
cleaning ( gently) but unsure if its on this engine ..

Thanks,

Nick

 

You can certainly *carefully* clean the AMM which is of the hot film variety
(or at least was) on your TDi. I would get a can of aerosol Brake Cleaner
(it is less aggressive than carb cleaner) with the attachable tube. After
removing the AMM from the car, you can carefully spray *across* the film
unit (i.e. the way air passes it) There is alittle hole inside which is the
sensing element. NB They are very delicate to high pressure! Gently rock the
unit and drain out the residue, allow afew moments for evaporation, and then
repeat 3 or 4 times until the run-off is clear..

This may improve your situation, though to be fair these do not last
forever, and after 165k it will be past its best.

If your hesitancy is generally on a light throttle and accompanied by some
soot, i would be diving right into the EGR valve, and blanking it off before
tackling the AMM...

Tim.
..

 

when engine is idling - if lower it could be the intercooler that needs to
be cleaned
or changed.
I had this problem with my 850 TDI, cleaning the intercooler restored the
pressure to
the desired value and the turbolack feeling became much smaller afterwards!

Another possibility is a vacuum leak desturbing the turbo pressure
regulation.

Best regards
Per

 

Hi,
Thanks for those tips - had not considered either so will check those too,

Thanks,

Nick

 

.....snip....

Just read again, - surely there will be no boost at all at idle ?

Nick

 

There will be no boost at idle- only when under load beyond 2000rpm or so. I
believe stock boost is 15psi (1bar)somewhere after 2500rpm. If its
appreciably low, then replace the wastegate diaphragm or wind up the rod
abit...

Tim..

 

Hi Tim
Thanks for the reply - I wasn't sure of the figures as I haven't got( can't
get) a workshop manual for this model
engine, although I think it is a variant of an Audi engine.... just had a
look at the engine - is the wastegate
on the top right of the exhaust manifold as you look at the engine from the
front, if you are familiar with this engine ?
Thanks,
Nick

 

The wastegate is on the turbo, circular tin capsule with a hose connected
mounted on the compressor housing, and a rod sticking out connecting to a
valve on the exhaust housing.

Tim..

 

You should measure around 1.5 bar when engine is idling this value stays on
at higher rew's.
Before I cleaned the intercooler the pressure was 1.2 bar at idling.
Under heavy accelaration I measure up to 2.4 bar at 4000 rpm. I am using the
VOL-FCR software
for the measures.

Cheers Per

 

Hi Per,

I guess this is absolute pressure you refer to - a turbo is not spinning
much at all at idle, but spins up at around 1500 rpm and above to boost the
pressure above ambient up to its pre-set level, determined by the wastegate
settings, typically somewhere between about 1/2 bar and 1 bar, or 7 and 15
psi. There is no "boost" at idle, unlike a supercharger which is crank
driven and may well be producing a little boost at idle.

Nick

 

Your explanation sounds logical. I am using VOL-FCR Live Data Stream option
and this
tool displays the desired boost pressure and the actual boost pressure at a
given RPM.
Cleaning the intercooler helped the actual boost pressure to equal the
desired boost pressure
at any RPM! I am sure that there are other ways to increase the boost
pressure.

Cheers Per