ThreeSheds Posted April 24, 2008 Share Posted April 24, 2008 Hi, Each morning I start the car (no/minimal smoke), I leave it ticking over for twenty seconds, I accelerate away in first (no/minimal smoke), I change to second (no/minimal smoke), I back off on the downhill approach to the corner at the end of the road and there is a HUGE puff of grey smoke from the exhaust. After this has cleared (maybe 50 yards) I get no noticeable smoke for the rest of the day no matter how I drive, including after leaving it standing for 4 hours at work. Any suggestions please? It doesn't appear to affect the car in any way but is a little embarrassing. Other information: I park it on a mild slope to the right due to having 2 wheels on the pavement. The oil is at the correct level but needs a change. On one occasion a month ago, it produced a full-on smoke-screen on the motorway and slowed to a stop. I tried re-starting it and the smoke cleared and away we went - this hasn't happened since... Quote Link to comment Share on other sites More sharing options...
Dorsetfreelander Posted April 24, 2008 Share Posted April 24, 2008 Does it tick over OK when cold? Does it start easily? This sounds like unburnt fuel in a cold engine which can be caused by a faulty glow plug. I used to have a Citroen ZX diesel that did this and it was tracked down to a failed glowplug although it would often throw out a load of black smoke if you suddenly accelerated on the motorway (which was normal), earlier diesels did this a lot but I have never seen it in the later common rail technology. Other thing to think about is a dodgy injector which is occasionally pumping too much fuel in and leaving unburned carbon in the exhaust. Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted April 24, 2008 Author Share Posted April 24, 2008 Hi, and thanks for the suggestions. It starts very well - even if I don't give it long on the heaters, and immediately ticks over fine hot or cold. Although I can't smell this smoke it looks like fuel smoke to me but I can't work out why it only occurs after the first start in the morning - and even then only on the over-run down to the corner - not on the 1st to 2nd change... I'm confused (not com) Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted June 14, 2008 Author Share Posted June 14, 2008 I have been experimenting and now have a little more information on this big puff of smoke problem. The following is me thinking out loud so will be disjointed and rambling: 1. it only happens on a cold engine. 2. It lasts for about 4 seconds and applying throttle during this time stops it 3. it only happens on the overrun - ie if I dip the clutch and use the brakes to slow down it does not happen. If I do this clutch-dipping for the first mile, then the smoke NEVER occurs 4. Once it has done it's big puff, it doesn't do it again. i.e. If I let it happen at the first corner then thats it - no more smoke, but if I clutch dip so that it doesn't happen at the first corner then it will happen if I let it overrun at the 2nd. As far as I can see, the controlling influences when the engine smokes are: revs high (2000rpm - high for a cold diesel anyway ) accelerator off (overrun) boost low Engine temperature low Not done it already today Could it be injection advance? When the revs are up at 2500 (say) the injection timing must be advanced a bit - could this, combined with a cold combustion chamber and low injection quantities (closed throttle) resulting in the diesel equivalent of a weak mixture, be the problem? but then why don't they all do that? Hmmm Sounds unlikely. Since they don't all do that, I guess that it must be due to wear/damage/maladjustment somewhere in my engine. What could be worn/damaged/badly adjusted? 1. injection pump 2. injector bodies 3. rings/valves etc (low compression) 4. carbon build up ? (I don't know what symptoms this can cause on a diesel) Why does it only happen once? Something sticking in the injection pump perhaps which having once stuck, then frees off? Thanks for listening. As I said it's just rambling thoughts on the subject - if I ever get to the bottom of this I will reports back... Cheers, Confused of Oulton Quote Link to comment Share on other sites More sharing options...
muddy_muppet Posted June 14, 2008 Share Posted June 14, 2008 Another thought for you: Excess oil that's settled in the crankcase breather, being drawn into the manifold just at that point? Quote Link to comment Share on other sites More sharing options...
SteveRK Posted June 17, 2008 Share Posted June 17, 2008 I would suggest that the fuel pump is not shutting off on the over-run (sticking) when the engine is cold. I dont know these engines but if there is a throttle butterfly involved this would prevent the fuel from burning properly and it collects in the exhaust? Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted June 18, 2008 Author Share Posted June 18, 2008 Thanks for the replies I would suggest that the fuel pump is not shutting off on the over-run (sticking) when the engine is cold. I like this idea - it fits the symptoms.. Ahh, but thinking further - if it was just staying stuck open I would expect the engine to keep pulling. If it is an internal throttle sticking thing then, to make smoke, it would also have to be causing the fuel to not ignite and I can't see how that would work. I dont know these engines but if there is a throttle butterfly involved this would prevent the fuel from burning properly and it collects in the exhaust? No throttle I'm afraid. I am loathe to think that fuel or oil collecting somewhere and then being burned or introduced into the exhaust is the problem because of the way I can prevent it happening by driving differently. It's not like it happens later or anything - it just doesn't happen at all unless I use engine braking within the first couple of minutes. However I can see no way that extra fuel into the cylinders would do anything other than cause the engine to pull harder (which it does not). Phew! I am still confused by this. I guess the only test for injection pump problems would be to fit another (especially since it's such a transient problem and unlikely to happen during any bench tests)... hmm - could be expensive! The good thing about all this is that I now know how to 'manage' it so as not to produce the smoke - so it's not urgently in need of attention Thanks again for the suggestions Quote Link to comment Share on other sites More sharing options...
SteveRK Posted June 19, 2008 Share Posted June 19, 2008 Before you 'bite the bullet' on another pump you could try lots of drastic mods like disconnecting the exhaust EGR, Brake Vacum servo (potentially dangerous i know) any other vent/breather pipes on the engine etc. Anything that should/could/might/would have some kind of effect to see what if any effect it has - Confused!!! Quote Link to comment Share on other sites More sharing options...
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