smokey diesels

[Vixter]

VoH has asked me to post this as he is away. " with diesel engnes being compression ignition, what causes the soot deposits? Is it incomplete combustion or poor injectors gving too much fuel and not enough oxygen to completely burn? What is the first thing to check and how do you do it" We dont think it is oil consumption as we have only used 1 ltr in 3000 kms He said," its normally aspirated indirect injection" what ever that means!! Vixter

[enodreven]

Hi, Vixter Obviously there are a number of causes, but one of the best and cheapest cures I have found is using a proprietary brand diesel injector cleaner from somewhere like Halfords and then driving the vehicle very hard for quiet a few miles, by hard I mean with high revs as this always seems to work for my old small ford van, albeit does chuck out a lot of black smoke and rubbish but that seems to work either before the MOT or every couple of months just to keep it running smoothly I always replace my engine oil every 4000 miles and if you were going to drive it hard make sure the oil is in good condition and topped up before you do, as it can be risky so be careful as i suppose you could blow the engine up if has any inherent problems, so don't blame me if anything goes wrong ? best of luck, i am sure someone else will be along with a better suggestion soon.

[Basil]

Have you checked the air filter? The only time this has happened to me was shortly after renewing the air filter in our Boxer it started to smoke a bit more than usual, when I checked the air filter it was contaminated with dirty black oil that had come through the breather system and was running inside the filter housing. I understand from discussions with a Peugeot Main Dealers technician after that this is not an unknown problem and when you change an air filter you need to ensure A) that the breather system is cleared, cleaned and washed out. B)that re-assembly of the filter housing and its connections are as they should be, with all arrows linning up and with the housing in the correct plane. Bas

[Brian Kirby]

With a diesel, the accellerator pedal connects (albeit sometimes via electronics) with the diesel pump that in turn supplies fuel to the engine.  Thus, when you press down on the pedal, the engine gets more fuel immediately, whether it has sufficient air to burn it, or not.  Result, not all the fuel burns properly and the unburned fuel emerges as soot or smoke.  After a while the poor old engine gets its revs up, gasps in some more air, and starts burning better.  The best way to reduce smoke is thus to change down, allow the engine to rev a bit more, and then squeeze the pedal down progressively rather than stamping on it.

The drive by wire electronic injectors do this so much better than we mere mortals, which is why the fuel consumption is so much better on engines so equipped.  We once had a Citroen ZX, which did around 40 mpg.  At the time I thought that quite good.  Our next car was a Citroen Xsara, which was drive by wire, did 50 mpg, and smoked a lot less.  Mind, the Zx was quite a bit quicker, and had the advantage that if you really wound it up it laid a perfect smokescreen so no one behind could see you!

[colin]

Putting 2 and 2 together to make 648, truck racers used to increase injection to get more power, but it was getting that hey where pumping out massive black clouds and restrictions where brought in, so I think its overfueling and or incomplete burning

[Dave Newell]

There are a couple of causes of smokey diesel engines. If it smokes all the time then its probably an injector fault, one of the proprietary cleaning treatments may help but it would probably be better to replace the injectors. If it smokes only on acceleration then it could be overfuelling which can only be remedied by a diesel expert with the proper knowledge. It could also be a mistimed pump although this is usually accompanied by difficult starting and a lack of power. The third and most likely culprit would be a dirty air filter and finally it could be a faulty EGR (exhaust gas recirculation) valve, Ford Transit 2.5 DI engines are prone to this particular problem. The above only applies to black smoke. If the smoke is blue then its engine oil being burned and the most likely culprit is worn valve guides and or piston rings/cylinder bores. D.

[dickyc2]

8-) good afternoon all, the one thing vixter doesn't mention is what vehicle is it, also check fuel filter, water causes diesels to smoke. Also if the engine is a turbo diesel and not revved hard enough the turbo soots up, and once that clears everybody behind you has to result to switching on headlamps, if it's a modern diesel, it could be a faulty EGR vacuum solenoid or split vacuum pipe.

[docted]

Vixter You have mentioned soot deposits, I will assume therefore that what is meant is the "lining" in the exhaust. If the vehicle itself is not smoking when being driven you have no cause for concern. If it is smokey when being driven, if the smoke is black, it could be related to under use. CHECK OIL AND WATER LEVELS BEFORE DOING THE FOLLOWING. I would reccomend that the vehicle is driven until the engine is working temperature and then driven hard, full throttle, through the gears for about 30 seconds in each gar at max revs this should clear out the poor things tubes. If as Dave says the smoke is blue you do have a problem which will require workshop attention soon. Docted

[Vixters other half]

Thanks for all the info I will be changing the Air filter although the little green guage says its Ok still - maybe the guage is choked as well. The engine is a MAN 6 Cylinder Rgds VOH

[Clive]

From experience with diesel Land rovers. Cause 1 A jubilee clip has slid back and the pipe from the turbo to the intercooler blows off when under load, ie no effective turbo boost. The fuel gets there but not enough air. However pop the bonnet and look and it all looks fine until you poke the rubber pipe and it moves away from the intercooler! Cause 2 You have been playing with the maximum mixture screw on the side of the pump (if its a mechanical pump). Fiddling with the CPU mapping if its fly by wire. (Add on black boxes which give more power will increase the likelyhood of smoking) Cause 3 The air filter has sucked in some water which effectively turns the dust into concrete. Only part of the filter then works restricting the air. Not uncommon to those who go wading!! Cause 4 The injectors are knackered or coaked up. Cause 5 An air sensor has partially failed telling the brain it has more air than it really does. I have had blocked fuel filters (waxed up) and these have never caused the engine to smoke, just to misfire when giving it some welly. Water makes engines either stop of badly misfire. Hope that helps.