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Over the last 12 months I have noticed that as I pull away and put my foot down a little more, there is often a bit more of a cloud of smoke left behind. Its not thick smoke but still it seems like much more than it was before.

Any ideas what I could look at to try and resolve the issue? Or is this just a normal thing for a diesel and I have become more aware of it?

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2 Answers

It's possible that the smoke you're seeing isn't indicative of any major problem. Some of the VW diesel engines have a tendency to build up unburned fuel and other deposits on the exhaust side of the engine if they're driven for short trips and driven too gently.

I don't have direct experience with the SDI engine, but this is a real problem for the TDI engines, and can lead to turbo issues on the TDI when the turbo eventually becomes too sooted up (especially on the variable-vane geometry turbo).

Prevention is relatively simple. Try to push the engine hard at least once per trip to burn off these deposits. After the engine has warmed to operating temperature, if you have a clear stretch of road in front of you, accelerate hard (floor the accelerator) in second or third gear all the way up to near redline. You need both full-throttle and high RPM to generate the heat to do the job. High RPM by itself won't do it, and full-throttle at low RPM won't do it.

You may find that the car smokes less after this.

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I mostly do short journeys (6 miles at a time) on 30-40 mph roads so to compensate for that I do make sure that I give it a bit of a boot as you said each day to clear it out. But it seems to give out the smoke every time. Its not a lot of smoke and is a less noticeable duing the day (more at night in the poor guy behind lights!). –  Penfold Mar 21 '13 at 13:52
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With such short trips making up the bulk of your driving, I'd say that this exhaust fouling is a likely cause of your smoky exhaust. –  mac Mar 21 '13 at 14:53
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To add on mac's answer, other than soot build-up on the exhaust there could also be a MAF sensor issue. The Mass Air Flow sensor reads the air that goes into the engine and regulates the diesel fuel quantity accordingly.

When this sensor begins to go bad it reads a higher value than real leading the engine to inject too much fuel which, of course, won't be burned but produce smoke.

The MAF sensor can be checked with a typical OBD-2 engine reader such as a cheap interface from eBay combined with VAG-COM software.

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