I'm currently having a problem with my 1993 MB 300D 2.5 Turbo, when I'm accelerating above 50mph and I let off of the accelerator to decrease speed, then increase speed I at times get this white puff of smoke out of the exhaust, it doesn't happen all the time, but I have noticed a decreased occurence after having my transmission serviced yesterday. Does anyone know what may be causing it? Any help would be greatly appreciated.

Is your engine temp. at normal operating temp. when this is happening? I only mention this because I recently had to replace my t-stat because I wasn't reaching normal operating temp. One side effect was puffs of white smoke while driving - even at high speeds. If the engine temp isn't high enough, then you won't be burning fuel efficently and unburnt fuel can lead to white smoke. Just a thought.

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'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
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"Back off, man. I’m a scientist” ~ Peter Venkman

unburnt fuel would be grey or black

I have white smoke come out of my exhaust when I first start up on a (relatively) cold morning. As it only lasts 60 seconds or less, I haven't really investigated it yet.

What's the oil consumption?

It's not uncommon for valve guides/seals to let some oil past during high rpm decels.

I wouldn't worry about it unless you're burning a quart every 1K miles.

I haven't noticed any significant change in oil consumption, had my oil changed about a month ago, I do notice a slight hesitation in accelerating when I get the white puff of smoke, almost as if the car is stuck in a gear for a sec or two, then it shifts, and thats when I get the white smoke. it usually lasts for l5-10 seconds, then goes away, and its white smoke, which really threw my mechanic off, because it wasn't blue, or black. which would've pointed to a specific problem. I thought it might have somethin to do with my transmission because it hesitated while shifting. I have the manuals for my car, I just can't find any mention of a modulator, or anything that might be sucking in transmission fluid, or oil into my exhaust and causing the smoke.

Yes, that is possible too. I guess my answer was too short.

Black smoke tends to develope as a result of the fuel to air mixture being too rich - so either too much fuel being delivered or not enough air.

White smoke could mean that the fuel being delivered is not being burned properly. The reason for white smoke on cold starts is because after it is atomized by the injectors, it condenses dues to the low engine temps. Generally, this is only temporary until the engine warms a little. However, if the engine never reaches a decent operating temp - like mine was doing - white smoke will persist.

Now, whether it is black or white, both symptoms could be caused by several different problems and I suspect others will list them. Let's just be glad it's not blue smoke!

Also, white smoke could indicate some water in your fuel. If it is unburnt fuel, then it would smell like fuel and probably burn your eyes (so I hear, I didn't want to stick my face in the exhaust). If it is water vapor - it shouldn't smell like fuel.

Basically, check all the easy and cheap things first. If those all check out, then consider a bad injector or injection timing. However, before that, just make sure you are at proper operating temp, you don't suspect water in the fuel (which can be more problematic in cold temps - maybe change your filter), and that you don't have air getting into the fuel lines.

__________________
'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

With the hesitation added, I would say first, make sure your fuel line is clear - so change the filters and maybe even check the tank strainer. If that doesn't work, then consider retarded pump timing.

Are you saying that there is hesitation which mimics the feeling of shifting - or are you saying that there is hesitation during the shifting process - when you wold normally expect to be shifting. So, hesitation throughout or just during normal shifting?

__________________
'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

It could be moistue in your exhaust system that clears up after it evaporates.

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84 300D, 82 Volvo 244Gl Diesel

its normal shifting, just if I let off the accelerator, it seems to slip down a gear, then once I apply the accelerator, it seems to hesitate as if it needs to shift, then shifts itself as white smoke exits the rear.

Agreed, white is water, correct? Light blue oil?

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83 SD

84 CD

It's not water........otherwise you'd be losing coolant in a big way.

The problem is either oil or fuel. I'd monitor the oil consumption to rule it out or not. If it's fuel, one injector is the likely culprit.........although I'd think that it would affect your idle in some fashion..........slightly rougher than usual.

hmmm didn't suspect a fuel injector, nor did it come to mind, I have located my modulator, and a vacuum line attached to it, that may have some oil or fuel in it which would cause white smoke. I'm just trying to figure out the best way to get to it, so I can detach the line and inspect it.

Well, white could equal water (moisture) and not necessarily coolant related - so, for example, some water in the fuel which often becomes more noticable when it gets real cold. However, I'm not sure that is the problem here. (Go cheap first and switch out those filters if you haven't yet) Since the white smoke seems to be happening at normal operating temps my first guess is that it is somehow fuel related - if you're positive the smoke is white (not bluish), which you seem to be. So a quess would be to check the injectors. Although I agree with Brian that you would probably be getting a rougher idle with a bad injector. If you are experiencing that (rough idle) you can follow the advice of others here and crack the injector lines and see if any one of them give you a noticable difference in the idle.

__________________
'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman

http://www.oceanmarineservices.com/Diesel%20Engine%20Smoke.htm

This is one link to look at, search here or google it. Some of what is said in this thread would apply to a gasoline engine, verify it.