V70 Tdi - cleaning airways advisable ?

Discussion in 'Volvo V70' started by Nick, Jul 7, 2007.

  1. Nick

    Nick Guest

    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 ..


    Nick, Jul 7, 2007
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  2. Nick

    Tim.. Guest

    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.., Jul 8, 2007
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  3. 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

    Best regards
    Per Groth Ludvigsen, Jul 8, 2007
  4. Nick

    Nick Guest

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


    Nick, Jul 8, 2007
  5. Nick

    Nick Guest

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

    Nick, Jul 8, 2007
  6. Nick

    Tim.. Guest

    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

    Tim.., Jul 9, 2007
  7. Nick

    Nick Guest

    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 ?
    Nick, Jul 9, 2007
  8. Nick

    Tim.. Guest

    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.., Jul 9, 2007
  9. 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
    Per Groth Ludvigsen, Jul 9, 2007
  10. Nick

    Nick Guest

    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, Jul 9, 2007
  11. 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

    Cheers Per
    Per Groth Ludvigsen, Jul 9, 2007
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