Swedish Smoking Saga - Saab Spannering.

[83C]

A friend has a 2006 Saab 9-3 TiD with the 150bhp 1.9 turbodiesel. It drives well, but has an odd issue where every so often it blows smoke out. Fuel consumption drops, the smoke is blue/black (via the wing mirrors) and it’ll smell of diesel. It’ll do it for up to 10 minutes, then back to normal. 

It sounds to me like the DPF regenerating, but it’s doing it on most journeys over 30 miles. Sometimes after half an hour, sometimes it’s done it several hours into a long journey. 

The car looks to have had a lot of new bits which we suspect was the previous owner chasing the fault. It’s been a to a normal garage but the owner isn’t near any Saab specialists. 

Anyone have any suggestions as to what this might be?

[Macscrooge]

Sounds like DPF regen, though 10 minutes seems a long time. Mine (a TTiD) only did it twice in 2 years but I borrowed one (a rather tired TiD) which did it twice in one day!  One for your Saab specialist I think. 

[Bren]

Car mechanics recently had a TTiD project car with the same issue - I don't think they resolved it.

[Inspector Morose]

Sounds similar to what my 06 TiD used to do. That was going through a regen. Mpg drops through the floor and occasionally there’s white smoke from the exhaust. There’s a distinct smell to it too, not quite fuel but that sort of thing.

edit: It wasn’t until I took it on some really long runs at a good speed that they became less frequent, a drop of dpf cleaner through the system sometimes helps.

[Noel Tidybeard]

could try the vw handbook method- drive a minimum 15 minutes at 45 mph in 4th gear- it worked when the light came on a 406!

[83C]

Thanks for the advice so far. 

What actually tells the DPF to do a regen? Is there some sort of sensor within the DPF that measures soot or is it dependent on what the engine management sees happening across the full combustion cycle?

[Surface Rust]

3 hours ago, 83C said:

Thanks for the advice so far. 

What actually tells the DPF to do a regen? Is there some sort of sensor within the DPF that measures soot or is it dependent on what the engine management sees happening across the full combustion cycle?

I can't speak for all systems, but some use a delta pressure sensor (pressure loss across the filter) and some use RF sensors to measure the soot loading. Some use both!

[Sham]

If it's doing overly frequent regens, then it probably isn't doing a thorough enough job of it. 

I'd suggest a long run at motorway speeds - at least a couple of hours. Maybe use a motorway for this.

If it keeps it up after that, it probably needs attention - but I wouldn't be unduly worried by regens with no other problems.

[83C]

Info all passed on. He may be selling it sometime soon, if so I’ll try and get him to either advertise it himself here, or let me stick an advert up.