Hi to everyone!
I recently bought myself a 2004 156 SW 2.4 JTD 20V M-Jet Facelift II. So far so good, the only problem is that the car has a strange, rather erratic sooting behaviour: Sometimes itís smoking like hell, sometimes not at all and this even in more or less same driving situations and comparable environmental conditions.
At first I assumed that the previous owner was always creeping around town in very low revs, which could have caused soot build-up in the exhaust systems. Then Iíve have tried using ďDiesel Soot StopĒ additive from Liqui Moly for a while in combination with Ė almost daily - higher rev driving on the motorway (3000-3800 rpm) for a few minutes.
Further I have visited a friend of mine who has an Alfa specialized garageÖ We checked all the known suspicious parts like turbo hoses, recorded graphs of different sensor data (Air mass set/actual comparison), water temp, etc. and everything was looking good. We didnít check the AGR though, as it was already cleaned 6000 miles ago. However as soon as I have some time, I will also check and clean the AGR again.
Iíll try to give you an example of why the smoking behaviour seems so odd to me:
Driving for 35mins with an average speed of 80 MPH on the motorway, afterwards I take an exit where Iíll slow down to about 35 MPH. Then Iíll accelerate to 70 MPH (~80% throttle) from 2000 RPM in fourth gear and this is when the car is smoking badly (easily viewable in the rear view mirror in daylight). Itíll keep sooting all the way up to 4000 RPM, but it doesnít seem to loose any power.
Then Iím driving in city environment (low rev) for another ten minutes until Iíll boot it (100% throttle) from 2000 to about 4000 RPM again Ė however in third gear Ė but this time there is no visible smoke at all!
Ok so then I though maybe itís really soot build-up from driving with 2200 RPM on the motorway, however this morning I tried clearing her throat just before taking the exit by shifting into 5th and even 4th gear for a few mins, yet I had still the exact same smoking when accelerating on that exit.
So do you guys have any idea how this is possible or explainable? Iím thinking that maybe the AGR is too slow in certain situations which could explain the erratic smoking?
I happy for every advice as its not easy diagnosing it with that snatchy behaviourÖ Some days I think itís all good, the next one Iím almost ashamed to accelerate harder.
Thank you in advance for all replys!
Greetings from Switzerland!