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Intermittent Grey Smoke from Exhaust

Cornish Boy

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Help - I purchased a 2018 Forester XC Premium 2.0 diesel with 48k miles and full history in Nov 22. Until 4 months ago everything seemed ok (now has 66k miles). After a run on a dual carriageway for example as I decelerate the engine feels like it has a retarder operating on the engine and then when you accelerate again plumes of grey smoke emit from the exhaust. This will not occur if you rev the engine in neutral at this point but only when a gear is engaged and you accelerate.  The engine then runs very "ragged". If you pull over, stop the engine for a few minutes and then start up again - all clear - until the next time !!!! I have had a diagnostic check at three different garages who say they can find no fault. After a few weeks of this the DPF light came on. DPF has been cleaned out and on running afterwards the diagnostic gave a clean bill of health to the DPF and confirmed that the EGR valve was opening and closing as it should. The analysis did show some minor oil dilution when the DPF was cleaned. Oil and filter has been changed. Car is not burning any oil and on a recent run from Cornwall to Cumbria and back via Oxfordshire it returned an average 58.9 to the gallon. I have taken it to three different garages of who all tell me they can't find anything wrong. Something clearly is - Any suggestions?

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  • 3 months later...

Had same with my 15 plate diesel - and it is a feature of the clogged DPF. Just before the DPF is egr and a temp Sensor in the box b4 DPF.. Check this sensor first. Presume you also get the booming exhaust whilst DPF is cleaning (egr active) ? Would advise keep checking oil level too- dilution can continue even when you don’t notice smoke- next to go is serious stuff- oil gets into the turbo…not good and £££. 
definitely a DPF issue - dealer based forced cleaning (fire ext handy) might solve short term. Other issue I found was a crack in the split exhaust manifold, which suggests air getting into DPF, creating soot and ash deposits- oil burning in DPF doesn’t then clean these deposits, so cleaning cycle repeats…even if system alarms thinks all is good..

Ended  up changing the lot- DPF, egr, sensors- ran fine with no smoke for 50k further miles.. add a dealer supplied DPF cleaner fluid every 6 months..they work.

incidentally, whilst mine was in for repairs, 4 others were too with same issue- there was a suggestion of biofuel / bad fuel batch. Not convinced. 

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