Sparks from exhaust?
 

I picked my car up from a major service at a reputable shop tonight, drove it about 45 miles at freeway speeds ( 75-80 mph, short bursts to 100 when traffic allowed ) and noticed sparks from exhaust area at rear of car when I let off throttle as I slowed for offramp! I stopped at first chance once off highway and couldn't find anythingh amiss.....I'll call the shop first thing but wondered if anyone else has experienced this....

I seem to remember reading a similar post a long time back, can't remember if it was here or at the rec.mercedes newsgroup. I believe the speculation at that time, was heated chunks of carbon being blown out the tailpipe, a result of the Italian tune-up.

Can't say I have ever seen this happen in a diesel, but have seen it with a gas engine, especially when the timing was off (or caused on purpose, old time stick shifters know that trick).

This is a common occurance in the buses I drive. Especially if the bus had been operated in a shuttle route in the city, lots of stop and go. Then taken for an Italian tune up. At night it made a pretty good show when I looked in the mirror.
The only thing that sounds funny though, is that I got sparks when I was full throttle, and you got them when backing off.

Could be that is just when the sparks slowed down enough so you noticed them.:D

The carbon build up seems to be a good theory....the car had been used primarily around town, less than 10k per year by older woman owner. I've driven it hard since I got it but not under full boost until tonight.

I did try a series of accel/decel runs and could only see sparks when I lifted throttle. The quantity of sparks diminished fairly quickly after a few times.

If the car catches on fire, I can always smother it with diesel fuel, right?

Ha Ha, I don't think I would try it. And you won't catch fire with the carbon build up crud.

I used to work as a laborer on a asphalt paving crew. We did a lot of shoveling and raking of the hot asphalt, and the stuff would stick to our shovels like mad (as you might imagine). So we kept a large barrel of diesel fuel to dip our shovels into, to coat them, so we could shovel into the asphalt. I remember the smokers in the crew would regularly throw their lit cigarettes into the barrell of fuel to put out the cigarette.:eek:

Now, this does sound familiar!

I got a huge cloud of burning soot out of my Volvo TD after topping a long grade outside Lousville, KY at night. I suppose the oily soot in the tailpipe caught fire on the up-grade, but there wasn't really enough air to get it really going, and when I let off the pedal at the top of the grade, there was.

Quite spectacular, the chunks appeared to be 1/2" or so, and bounced down the highway behind me the rest of the way home.

The origin was, I think, a combination of oil from the dying turbo (it locked up the next year) and excessive soot from a sticking EGR valve (on the Volvo, if it sticks open at full throttle, you be HUGE clouds of dense black smoke, very impressive).

I ended up with a new exhaust system, I suspect partially becuase of the fire, but at 180,000 miles, I wasn't too surprised it was bad.

Check your turbo for oil leakage, and disconnect the EGR to help prevent a re-occurance. You may have just had a huge collection of soot in the mufflers.

Peter

Re: Sparks from exhaust?
 

I've witnessed something similar about 18 years ago at a truck race in Poconno, PA. A 1000hp Cummins 855 was running around the track with a reddish orange glow coming from the stack - a constant glow extending about 1 foot from the exit. It continued for several laps until a turbo fire retired the vehicle. That clearly was unburnt fuel stemming from serious overinjection which ignited when released to a more oxygen rich environment. I would tend to agree with the others that in your case, the sparks are probably from carbon particles releasing from areas close to the exhaust valves or manifold.


1989 735i
1987 740GLE
1985 Jetta TD
1987 300 DT
1985 Mack MS200
1992 Kenworth w900 (Cat 3406)
1985 Freightliner fld (Cat 3406)
1978 Dynahoe D200 (471N Detroit)
1990 UD 1800
1989 Ford f350 Dually 4x4 (7.3)
1980 300SD
1986 900turbo
1980 Rabbit Diesel ( 48 squirrel power)

When we cut the old exhaust system off, it had at least a quarter inch of soot it in, mostly glassy. Both mufflers were about half full, too. Front pipe was clean, probably from being on fire!

Peter

exhaust
 

my rear muffler literally fell / broke off the car due to excessive
weight!! it was left on the road cause when we went to retrieve
it , it felt like it weighed over 100lbs! it must have been completely
filled with carbon.. :D Sure glad that it didn't catch on fire ..