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1995 Mercedes S420, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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Discussion Starter #1
Never had anything like this happen before.

I need to replace the caps & rotors on my car and I have it scheduled for this weekend. I'm still driving the car because it's mostly fine other than the odd misfire or stumble, but when it rains the moisture really gets to it and the situation can become worse almost to the point where it could stall. Not a big deal overall though and I already have the new parts.

Anyway, this afternoon I was running an errand and got caught in the rain. The car began to act up, but I was on my way back home anyway so I figured I'd just baby it home and leave it at that. At one point I was stopped at a light, uphill, and I felt the car stumble and almost stall, so when the light changed I got on the gas to try and power through. Got up the hill and through the intersection slowly, then was fine for another couple of blocks until I got to the next light.

I started to smell smoke, and it became more pronounced. Soon it began to really smell like something burning, almost as if someone lit a match in the cabin. I didn't see any smoke though and everything else on the car seemed fine, no overheat or bad oil pressure or anything. But the smell was getting worse. Thankfully at that point I was only a block away from home, and I popped the hood as soon as I pulled in the driveway and shut down the car.

That's when I saw smoke absolutely pouring out of the engine bay, from the top on the engine -- see the video I linked to below. I worried that maybe something had caught fire, so I took the engine covers off and got a flashlight to inspect what I could see. By the time I got the covers off the smoke had stopped and I couldn't see any evidence of anything burning. I turned the car back on and ran it for a while, but the smoke didn't return.

Any ideas on this one? The smoke really didn't smell like an oil or fluid burning. It literally smelled like someone had lit a pack of matches on fire or some paper or something.


https://streamable.com/5bbap
 

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1995 Mercedes S420, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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Discussion Starter #3
It's a 1995 S420, 168,000 miles and otherwise in perfect running order.
 

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1994 S500 Coupe
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Something started burning for sure.

Looks like smoke was coming up past the windshield too.

I'd really start rooting around and looking for whatever could've burned. Maybe even check as much as you can behind the dash.
 

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1995 Mercedes S420, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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Discussion Starter #5
Yeah those were my thoughts also. No smoke entered the cabin at all, so wherever it was it didn't get into the ventilation system. All the smoke appeared to be coming up from between the engine and the firewall and nowhere else, but I can't imagine what's in that gap that could have burned up. Maybe some leaves got in there?

I'm going to look more closely tomorrow but I just want to have some idea of what to even look for. But from my initial inspection tonight, nothing looked obviously wrong and the car didn't malfunction or throw a code or anything.
 

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Best of luck to you,hopefully it's nothing to serious....By the way what brand shocks are on your car and how's the overall ride????
 

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1994 S500 Coupe
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Yeah those were my thoughts also. No smoke entered the cabin at all, so wherever it was it didn't get into the ventilation system. All the smoke appeared to be coming up from between the engine and the firewall and nowhere else, but I can't imagine what's in that gap that could have burned up. Maybe some leaves got in there?

I'm going to look more closely tomorrow but I just want to have some idea of what to even look for. But from my initial inspection tonight, nothing looked obviously wrong and the car didn't malfunction or throw a code or anything.
No idea what to look for, aside from wiring, which would cause all sorts of issues. There really isn't anything back there that should burn.
 

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1995 Mercedes S420, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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Discussion Starter #9
Has your wiring harness been replaced? If yes then I would guess it's an oil leak
Wiring harness is only a few years old. What would leak oil back there?

No idea what to look for, aside from wiring, which would cause all sorts of issues. There really isn't anything back there that should burn.
I thought that also, but as you said, for a wiring issue to cause that kind of smoke it would certainly cause noticeable problems with the car in general. But I'm not getting any lights on my dash or any issues with the car at all.
 

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"CHRIS" Merc 92 600SEL / Sold > 93 600SE / 93 S500 / 89 560SEL / 413CDI / B180-CDI /A170-CDI
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Thom ,the only think i can think of what happen'd there is like what happen'd to myself ,just that my smoke was 4 times as much (v12).
What created that was ,when i pulled my manifold etc etc of to repair the small water hose behind the engine ,while i was waiting for parts ,i couldn't resist not to clean the engine ,so i de-greased everywhere including over booth Distributor caps .
Now ,after i re installed everything , engine started 1st go but the smoke it made was a fair bit ,the whole garage disappeared .
HERE is the interesting part , I thought driving the car a while will unblock what ever is blocking as i done this once before . No go with that just smoke .
I decided to pull apart the Distributors & Voila ,Oil & liquid all over it & behind the plastic caps . The center electrode was also welded to the center of the Dizzy Caps slightly .
The pressure with the engine not running properly resulted with un-burned fuel etc smoke to accumulate until it is to much then it escapes through any opening under the hood.
Pull your Distributors ,clean them & make sure the SEAL around it is nice & shut .
Before the Distributor pull out car almost stalled & misfiring a little but when accelerating hard ,she went good , the exhaust note sounded like an F1 car (my exhaust is modified ),i actually liked it ,lol.
No Cluster lights were on with this defect ,not even ASR .
Mine stopped Smoking (except my self) after that & car runs 110% since then ,absolutely PEEEEEEREFECT .
 

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1995 Mercedes S420, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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Discussion Starter #11
Ah... very interesting. I have new caps and rotors on hand and will be doing a full replacement this weekend. Let's see if that does the trick.
 

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1994 S600 Coupe, 1995 S600 Coupe
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Could be just a piece of paper road debris got thrown up and wedged next to a catalytic converter and burned. Cats get hot enough to do that.

Jon
 

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"CHRIS" Merc 92 600SEL / Sold > 93 600SE / 93 S500 / 89 560SEL / 413CDI / B180-CDI /A170-CDI
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Could be just a piece of paper road debris got thrown up and wedged next to a catalytic converter and burned. Cats get hot enough to do that.

Jon
You not wrong about that Jal .Here the Cats create Grass fires which then result in huge fire ,with Thom here ,it was raining so chances for that to happen are slim . I'm convinced it;s his Dizzies.
 

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Has your wiring harness been replaced? If yes then I would guess it's an oil leak
Using a used wiring harness is definitely taking a gamble and I was thinking about buying a used one also but then I just decided to order a brand new one one for my 96 S420 and yeah it was expensive $1300 but at least I'll have piece of mind knowing it'll be good for the long haul...
 

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1995 Mercedes S420, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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Discussion Starter #15
Did my caps and rotors, even removed and cleaned the insulator shields (aka 'dust caps'), applied dielectric grease around the gaskets to keep moisture out... and no dice.

Still doing the same thing as before. Running EXTREMELY rich (exhaust smells like pure gasoline basically) and making almost no power.

No smoke or anything, that only happened the one time, but all the symptoms are still there. Any ideas?
 

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1994 S600 Coupe, 1995 S600 Coupe
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Fuel regulator diaphragm shot and dumping raw gas in the intake? Don't run the engine much as you are washing down the cylinder walls. Also, run Mercedes STAR diagnostics, and look for codes.

Pull the dipstick, and smell the oil. If it smells like gas, changeit, as it's been thinned with gas.

Jon
 

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1994 S500 Coupe
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No idea why it'd be running rich, but what I'd be doing first if this was my car, I would be looking at my SDS and checking the actual values of the fuel injection computer to check for anything out of spec.
 

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1995 Mercedes S420, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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Discussion Starter #18
Fuel regulator diaphragm shot and dumping raw gas in the intake? Don't run the engine much as you are washing down the cylinder walls. Also, run Mercedes STAR diagnostics, and look for codes.

Pull the dipstick, and smell the oil. If it smells like gas, changeit, as it's been thinned with gas.
Fuel pressure regulator is only about a year old and was replaced with an OEM unit, so I'd be surprised if that was it, but it's as good a theory as any.

I pulled the dipstick and smelled the oil, and it did seem to smell like gasoline. But I never tried to smell engine oil before so to get a frame of reference I also did the same on my other cars. My Land Rover didn't smell as much like gasoline, and my Lotus seemed to smell more like gasoline. I have no idea what any of that means, but bottom line is yes, my dipstick did smell like gasoline somewhat.

No idea why it'd be running rich, but what I'd be doing first if this was my car, I would be looking at my SDS and checking the actual values of the fuel injection computer to check for anything out of spec.
If it comes to that, I'll be bringing the car to my mechanic. I'm not equipped to do that kind of work myself.
 

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1994 S500 Coupe
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Could do the old disconnect the MAF while it's running trick that I see around here. Pretty sure that's how it's done. It's supposed to force your fuel injection computer to use a default adaption table.
 

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1994 s600 coupe
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there seems to be a misconception about how to diagnose engine problems - a video of smoke coming out of the engine means nothing ?
mechanics don't have x-ray vision, what you have to do is, take the covers off and look CLOSELY with a light where the smoke is coming from ?
epiphany will strike, you'll see it quickly. it's not something that can be diagnosed with a video like that, you need to see down into the engine,
at the actual lines, components, wiring as to which one it is.
think of it as like a doctor, you have chest pain, what does he do- he takes an X-ray first. to see inside. or does an exploratory to look inside.
that's what you have to do. in addition to scanning the car with a computer scan tool.
it may be the fuel regulator but doubtful because you'd smell gas and the car probably would have caught on fire by now.
but maybe...
 
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