Intermittent black smoke and poor running

paul in normandy · Unread post by **paul in normandy** » 29 Jan 2010, 16:04

Our recently acquired (for free) Berlingo is playing up in another way now.
On the trip back from England I noticed the occasional 'flat spot' where it appeared to slow down and be struggling to pull very well, obviously much more noticeable going uphill. Going out in it today this condition was much more pronounced and seemed to happen more often. I also noticed that the 'flat spot' was accompanied with clouds of black smoke. It seemed to go like this for a while and then clear, the car would pick up, accelerate quite happily and the smoke cleared. This happened several times, but as we live out in the country it did not cause too many problems - not much traffic. The engine is a diesel 1868 cc DW8 WJZ unit. Having read several threads on here with cars having similar symptoms, am I right in thinking that one possibility may be that the air / fuel mix is being altered by something intermittently blocking the air going into the engine, or coming out the exhaust - for example some sort of flap in the inlet / or debris in the exhaust? The car does not sound noisy. I have also checked the air intake as far as the part that goes over the rocker cover. Just before that there is a small cylindrical unit on its side, with a blue cover to the right of it which appears to have some sort of flap / butterfly inside it. (The plastic cover is attached to the top of it). There seems to be quite a lot of soot inside here. Rain and a biting easterly wind stopped any further investigation. The air filter was almost new, backing up the information that the car had just been serviced in the garage before we got it. Am I looking in the right places to start with, before investigating the possibility of a blocked / worn injector.
Its got 340,000 km on the clock, but its local so probably not a lot of stop / start motoring.
Any help would be greatly appreciated.

rmunns · Unread post by **rmunns** » 29 Jan 2010, 22:57

First thing I would try is a generous helping of injector cleaner poured into the fuel. Any motor factor will have it.

Unread post by **Peter.N.** » 29 Jan 2010, 23:04

Check the air intake pipe for sign of possible collapse, it can do that at high revs if its damaged or perished, especially if its a turbo.

The 'sooty' bit you found is proabaly the EGR, exhaust gas recirculation, when working properly at small throttle operation it cuts NOX emmisions but it can go faulty and stick open, that also could give you the symptoms you mention.

paul in normandy · Unread post by **paul in normandy** » 30 Jan 2010, 09:22

Will go and have a further look today - at least its dry! Is there any way of testing whether the recirculation thing is working or not, or is it just a matter of muck out and test?

Unread post by **Peter.N.** » 30 Jan 2010, 09:28

You should be able to disable it but I am not familier with that engine, I'm sure someone who is will be along shortly.

paul in normandy · Unread post by **paul in normandy** » 30 Jan 2010, 09:47

I can see the logic of it, presumably if I can temporarily wedge it in the open position to allow a free flow of air it should prove one way or the other whether its that which is at fault.

Unread post by **Peter.N.** » 30 Jan 2010, 14:31

Possibly but on the XM you can disable it by disconnecting a plug but don't know if yours uses the same system.

paul in normandy · Unread post by **paul in normandy** » 30 Jan 2010, 14:52

I've just had a look, there is a plug in thing underneath, but true to form its right underneath and I'm trying to fathom out how to disconnect it.
Re my other post, at least I've managed to get the sidelight out, so some progress made!

paul in normandy · Unread post by **paul in normandy** » 15 Feb 2010, 17:38

Passed the CT (MOT) no problems today with the EGR valve disconnected so I guess I can put off doing anything about it for another 2 years!