Yesterday I arrived home as an old friend of mine stopped by in a smoking (literally) '96 E320.

I opened the hood and something smelled like it was on fire. Because it was coming from behind the engine, I used the garden hose to supress the smoke, but it did not stop rising.

Okay, so I am thinking that he burned up the transmission or something. I checked the dipstick just for fluid. It was there and the same for the engine.

At this point, the smoke is freakishly rising and I felt that it would become a very serious situation and very soon.

I looked under the car and no fluids were leaking, but upon hosing down the downpipe and the transmission, the cats got wets and emitted steam INSTANTLY. They were so hot that cold water straight from the garden hose would vaporize upon contact. I know they get extremely hot, but not like this. They kept smoking for a few more minutes and even after that time and cold water, they were still vaporizing water.

I asked my friend how far he drove. He said it had only been 1.1 miles since he left his home and said that the car had rough idle and made strange exhaust sounds as if it were firing cannon ***** at times within the drive.

I am led to believe that they are "clogged" up, but how does this happen and why without reason? Any ideas? The car starts, but has no power in any gear.

 

get very hot,more then boiling hot any time the car is fired up.Smoke would not come out of a cat in the engine compartment.If it got plugged and went on fire as they sometimes do the smoke would come out the tail pipe.Cats operate at over 500F boiling water is only 212F,so water will always steam on a hot cat.
What did the smoke smell like?Oil?Sweet like coolant?What color was it?
What temp was his gauge at?
You need to dig deeper and look for a leak of any fluid that may have gotten onto the exhaust pipe.
Early 96 were prone to head leaks at the front and the rear of the head,also prone to wire fires in the poor insulation and wire they used.
Don't let him drive it till you find the problem.The wire fires have caused many cars to go up in smoke.
ohlord

 

It was only after spraying the cats with water for a few minutes (and no other action meanwhile) that caused the excessive smoke to stop.

I believe gasoline was burning inside of the downpipes and cats. Not enough/normal pressure was exiting the exhaust!

Temperature was in the safe range.

 

Fluid leaking onto the exhaust would not cause rough idle, or the sounds the exhaust was making.

I forgot to add, the smoke was coming out of the sides of the car as well. It was just heavily noticeable from behind the engine when the hood was opened. The smoke was white with a bluish tint and smelled like something burning like I have not smelled before.

 

if raw gas made its way into the cat and went on fire,which like I said they do at times.Where was the smoke exiting?It can only come out the ends of the pipe unless a hole exists in the cat or the pipe or it left via the o2 sensor bung.You can run the car and check if the cat is bad with a infrared temp gun.
No codes?
Find someone with a lift and Inspect some more.Then check the wire harness if it looks like frayed mummy cloth and the wires inside are shy of their plastic coating.
ohlord

 

I have noticed that "drying out" of the insulation within the rubber ignition wires. I think they are poorly designed and dry under engine heat temps.

Could it be possible that due to this error with the ignition wires, (as I have seen on a '94 E320) 4 or 5 of the spark plugs work and the cyclinders belonging to the others would only be pushing out unburned mix?

I am very curious as to where the smoke is exiting, perhaps at the O2 sensor, but it was certainly rising up the downpipes and behind the engine as well as making a cloud of smoke around the cats but not behind at all. I am also stunned as to why the tail pipes showed no evidence of this smoke, but only a lack of exiting pressure instead.

 

the m104 up to about early 96 it was the actual wire harness that self destroyed itself.
Maybe the cylinders misfiring did cause the back fires he heard , his timing chain may have broke and thus the smoke and loss of any exhaust pressure coming out the tail pipe.
http://www.mercedesshop.com/Wikka/M104WireHarness
http://www.mercedesshop.com/Wikka/M104HeadGasket
can he get it started?If so any check engine light on?
ohlord

 

The cats do break and clog, but I don't know what the symptoms are (thank God). I don't think you can rule that out. If you have no leaking fluids, what else could it be?? Engine harnesses emitting clouds of smoke should also be obvious, although it could also cause the misfiring (backfiring?).

On my M104, the ubiquitous engine oil leaks always blew back onto the exhaust and created smoke, but it was clear from the smell what it was.

 

It starts but has no power in any gear. No lights on in the dash.

 

drive?
ohlord

 

I am currently hesitant to drive it, but putting it into "d" or "r," yeilds a lack of power and so the car is not ready to hit the road. I am stuck as to what to look at first, and it hurts that I don't have too much free time lately.

I think I will begin by looking at the ignition wires.