I've been reading through various threads over the last 2 to 3 years on the topic of Alfa Diesel 'coughs'. I have a 2009 159 JTD Ti 2.4 wagon/estate and it's hands down drop dead gorgeous. It has about 63k km's on it now and for the last 15k-20k it has sadly developed this annoying cough. I've read some of the comments and I would like to detail what I have done in order to try and fix it (which to date I have not):
1 - Injector cleaning - all 5 injectors were taken out and professionally cleaned by a mobile Bosche mechanic. This did nothing although probably extended the life span of them so I wasn't too unhappy.
2 - MAF sensor replaced - This did actually cure the problem however withing 3 weeks it was back. I don't believe it was realted.
3 - EGR - Cleaned, checked, tested by same Bosche mobile mechanic. No dice, no change whatsoever.
4 - DPF - This has had more Wynn's DPF cleaner in it than I care to remember. Although it seemed to have an effect, it wasn't consistent and the percentage blocked readings always ended up at the same % (I have all the software and connection leads to activate a DPF regen)
5 - Running on higher RPM to engage regen - for some time, I traveled to work (40 minute trip of which 20 mins is at around 100km/h in manual mode and keeping the revs above 3000 rpm. Sometimes when I got to work and cruised into the carpark, the engine/exhaust has a deep rumble to it which gave me cause to think I had initiated a DPF regen. However, this did nothing to the coughing situation.
6 - Back drilling the DPF - I got so fed up with the DPF cleaner that I back drilled the DPF after cleaning it out with an industrial pressure washer. This was the several holes version that go through 2/3rds of the DPF, leaving the forward 1/3rd intact. Noticeable increase in performance and response but coughing continues.
7 - Full fuel tank - Thought this had an influence, the fuller it was the less coughing but I'm not convinced now.
8 - New fuel filter - Alfa laughed at me for that one. I've kept the perfectly ok one I replaced in case I need a spare as there was nothing wrong with it.
9 - Now this is weird but I genuinely think it is relevant. Travelling around corners makes it cough violently. There is gentle-is left hander in a 60km/h zone as I leave work and it is guaranteed to cough. Sometimes it is really quite harsh, more harsh than any straight line occurrences. In a similar way, it coughs when I go through a small chicane on the way to work and the left hander after it.
10 - It happens at around 2000 RPM under light acceleration. I've even managed to make it cough on cruise control by setting the speed and using it to increase the speed when on a shallow incline at around the RPM range.
I have spent roughly $3000-$4000 trying all the suggestions on the forums and advice by diesel mechanics. I've posted my findings here so that you can at least ignore the points I'm convinced had no effect.
My latest hypothesis is that it is wiring related and a suggestion in this forum mentioned it could be the injector leads. It's possible that lateral 'g' forces disturb a fault in the leads and that's why it happens more on corners (I know I'm reaching a bit here but I'm running out of reasons).
Alfa would love to have it in but a) it's way out of warranty and b) the chief mechanic has suggested it may be cracked inlet manifold, head issues or worse and given that all the suggestions so far that mechanics were convinced would fix it havent, it's a last resort. the garage bill for that would be probably 2/3rds of the car value.
Anyway, I'll keep an eye on this thread and see if anyone updates it. If I have any breakthroughs I'll post it here. I have some contact cleaner which I will try tonight. When the diesel mechanic replaced the MAF sensor it was faultless for a few weeks and I wonder if some of the wiring was disturbed in that process which cured it for a short time.
I still love it though and I'm not giving up. There is a problem in there and I will hunt it down