OWNER a777fan (E420)

[gsxr]

Quite grumpy this AM. The warm misfire is back. I've had the caps and insulators off several times in the last couple weeks without an improvement. Grasping at straws ATM. Last time I checked wires were fine. Cap and rotor are only a couple thousand miles old. No 'moisture' behind the insulators...

All suggestions to avoid the parts cannon welcome!

Jon, without going back over 599 posts... how old are the insulators, how old are the wires, and (for grins) what brand cap/rotor are installed which have 2kmi on them?

Also: How bad of a warm misfire are we talking about here? Running on 4 cylinders, or 7-ish? All rpm / all load, or only certain RPM (idle?) or under heavy load? Does it go away after sitting a couple hours and remain smooth until the next day? Etc.

 

[a777fan]

Hey Triple Trouble,

Have you checked codes?

How bad is the misfire -- severe or just an occasional hiccup?

May be a good idea to throw a fuel pressure gauge on it to see what that does with the car running -- that would eliminate fuel supply as an issue.

Only other fuel related issue I could imagine would be an injector, but that seems far-fetched as the injectors are pretty bone-reliable and long lasting.

Lastly, and this is the real crux of my advice -- if you can put it on an old-school Sun oscillosope that can show each of the cylinders and their electrical pattern ("heartbeat"), that could identify any electrical anomalies, that would be super helpful at pinpointing which cylinder(s) is causing the misfire.

From there you can troubleshoot each of the items in the ignition chain for that specific cylinder, starting with the plug, and working your way back to the coils via the wires, distributors/cap/rotors, then the coils, and then back to the EZL computer (which is not your problem here).

I once had an stumble with my 560SEC many years ago, it was stumbling and running slightly rough. I took it into my shop in Portland, and they immediately put it on a scope and checked out each cylinder's heartbeat graph. It was instantly apparent that cylinder #4 was misfiring. It turns out that it was a ceramic insulator/suppressor in the end of the spark plug wire, where it attached to the spark plug. This was causing a direct spark to the cylinder head, instead of into the spark plug. A $20 suppressor screwed onto the end of the plug wire, and all was well with the world again.

The M119 wires are of a different design, but the troubleshooting concept remains......

Talk to Steve Geyer in Seattle (he's a member here if you don't know him) about getting your car onto a scope at his shop. If he doesn't have one, I'm sure he'll know someone who does and who can help you.

Ger, no, I have not delved in yet, but will, likely tomorrow night or this weekend. Will start with the codes and go from there. Will do a fuel press check, but since its consistently only after the temp gauge hits the 80c mark and slightly above, I think its got to have something to do with the finicky electrical system. I ‘treated’ myself to a picoscope last year, so this might just be the time to get re-acquainted with/learn more about it!



I do know steve. He’s a great guy. Was just thinking about him the other day actually. Was going to reach out and see how him and his family have been fairing through this mess. The misfire itself is multiple cylinders. The car is quite lumpy and on the verge of stalling when it occurs.

Thanks as always for the thoughtful reply, i’ll be reporting back with my findings.

 

[gerryvz]

My guess is a coil.

 

[a777fan]

Jon, without going back over 599 posts... how old are the insulators, how old are the wires, and (for grins) what brand cap/rotor are installed which have 2kmi on them?

Also: How bad of a warm misfire are we talking about here? Running on 4 cylinders, or 7-ish? All rpm / all load, or only certain RPM (idle?) or under heavy load? Does it go away after sitting a couple hours and remain smooth until the next day? Etc.

Dave, thanks for the reply!
I replaced the caps and rotors with OE from MB earlier in 2019 when I was having similar issues. I’ll have to look at them this weekend to get you the specific brand. I can’t rememeber if there are multiple providers for the OE part.

Insulators are original as far as I can tell. i certainly haven’t replaced them. As are the plug wires. I had to replace one or two of the plug boots that was out of spec a couple years ago, but as of last spring when I replaced the caps and rotors, everything was in spec. Both for the wires and plug boots. I’ll have to recheck them this weekend.

The misfire itself starts out as small ‘bites’ but quickly degrades into multiple cylinders and completely affects drivability. In gear idle seems like it will stall, neutral idle is better but the misfire ‘bites’ are still there.

I’ll likely start with codes, check fuel pressure, and then check the primary coil sigs this weekend with the pico to see if I can narrow it down. I’m certianly still learning that tool however, so the possibility of misdiagnosis or missing something is high!

 

[a777fan]

My guess is a coil.

me too actually. I remember looking at the primary signatures last year and seeing a slight variance. Perhaps one has kicked the bucket!

 

[nocfn]

INSUL t u later

change the insulators too just be done with it!

 

[a777fan]

Today was not all bad. My new suspension parts arrived from Naperville!


Here are some closeups for all you part nerds out there. Front struts are Sachs from Turkey:

Rear shocks are Bilstein!

Front coils are from GB:

and have been on a shelf awhile:
Rear springs are German, and appear to have recent date codes!
All other parts are Made in Germany, except the strut mounts, which are sourced from Turkey now:

Now that I know I have ‘blue stripe’ springs I can go ahead and order the pads. IIRC, gsxr and klink mentioned there is a specific recommended pad setup that goes with your ‘blue’ or ‘red’ springs. I am interested in a lower setup however while still not ‘rubbing’ with my yet un-purchased 16” 8 hole wheels. I’ll have to reach out to northNH to get his take on how ‘low-I-can-go’!

 

[gsxr]

Looks great, Jon! Say, what's the COO on the strut mounts? Last ones I got had no label.

 

[a777fan]

Looks great, Jon! Say, what's the COO on the strut mounts? Last ones I got had no label.

Thanks Dave! Excited to sort out the ignition issues then put this stuff on. The mounts? You mean the part in the last photo? Or something else?

What I would call the 'mounts' are in the last photo and they are from Turkey.

 

[gsxr]

What I would call the 'mounts' are in the last photo and they are from Turkey.

Yes! That is it - thanks!!

BTW, blue stripe springs are longer/taller. You may want to go with a thinner rear pad, slightly thicker front... charts are in the EPC footnotes.

 

[a777fan]

INSUL t u later

change the insulators too just be done with it!

*choke*

uh... new OE via MBOEMPARTS are $144 EACH?!

 

[Kyiv]

@a777fan, suspension is for your 500E, correct? Or sportline bits for E420?

 

[a777fan]

@a777fan, suspension is for your 500E, correct? Or sportline bits for E420?

Sportline bits for my 420.

I ... do not... yet have... a 500....

Pedestrian till I die!!!!

 

[gerryvz]

Bosch are about $50-55 each.

 

[a777fan]

Bosch are about $50-55 each.

Excellent. Good quality I assume?

 

[gsxr]

Excellent. Good quality I assume?

Yup, same as what the dealer would supply, at 1/3 the cost.

 

[Jlaa]

Today was not all bad. My new suspension parts arrived from Naperville!

View attachment 104471
Here are some closeups for all you part nerds out there. Front struts are Sachs from Turkey:
View attachment 104472
Rear shocks are Bilstein!
View attachment 104473
Front coils are from GB:
View attachment 104474
and have been on a shelf awhile:
View attachment 104475Rear springs are German, and appear to have recent date codes!
View attachment 104476All other parts are Made in Germany, except the strut mounts, which are sourced from Turkey now:
View attachment 104477
Now that I know I have ‘blue stripe’ springs I can go ahead and order the pads. IIRC, gsxr and klink mentioned there is a specific recommended pad setup that goes with your ‘blue’ or ‘red’ springs. I am interested in a lower setup however while still not ‘rubbing’ with my yet un-purchased 16” 8 hole wheels. I’ll have to reach out to northNH to get his take on how ‘low-I-can-go’!

I don't know how you handle two parallel restorations - one of Uter and one of your e34 BMW. Just one is a massive undertaking, but doing two in parallel, with duplicated efforts in parts research / mistakes / etc. That's impressive. We should call you @JC220 West or @JC220 Jr. or something.

 

[a777fan]

I don't know how you handle two parallel restorations - one of Uter and one of your e34 BMW. Just one is a massive undertaking, but doing two in parallel, with duplicated efforts in parts research / mistakes / etc. That's impressive. We should call you @JC220 West or @JC220 Jr. or something.

thanks jlaa.... but lets be honest. The quality of my work does not come anywhere close to that of the mighty @JC220. I dabble. That man is an absolute craftsman!

 

[Kyiv]

the mighty @JC220. I dabble. That man is an absolute craftsman

Yeah... It's extremely depressing to see his cars' engine compartments. His posts make me feel small and insignificant. The man is a wrecking ball to other men's egos.

 

[gerryvz]

It seems that @JC220 is the new Lowman.

 

[a777fan]

It seems that @JC220 is the new Lowman.

RIP

lol

 

[Jlaa]

RIP

lol

I dunno. @JC220 has always been on another level. I mean both lowman and jc220 shoot for perfection, but only jc220 will decide to pickup a couple of spare transmissions for parts hoarding purposes.

 

[gerryvz]

The problem with @JC220 is that he has gotten radically sidetracked by pesky W140 models, door closing pumps and over-complicated electronics. Shiny objects and all that...
.

 

[JC220]

I don't know how you handle two parallel restorations - one of Uter and one of your e34 BMW. Just one is a massive undertaking, but doing two in parallel, with duplicated efforts in parts research / mistakes / etc. That's impressive. We should call you @JC220 West or @JC220 Jr. or something.

To qualify you require at least 3 unfinished projects too

thanks jlaa.... but lets be honest. The quality of my work does not come anywhere close to that of the mighty @JC220. I dabble. That man is an absolute craftsman!

Thankyou man I appreciated it!

Yeah... It's extremely depressing to see his cars' engine compartments. His posts make me feel small and insignificant. The man is a wrecking ball to other men's egos.
View attachment 104560

I dunno. @JC220 has always been on another level. I mean both lowman and jc220 shoot for perfection, but only jc220 will decide to pickup a couple of spare transmissions for parts hoarding purposes.

My own Meme!! That gave me a good chuckle thankyou for your efforts

This is a fair observation and I am also hoping to soon pick up spare transmissions for car's I havent bought yet which is a whole new level of illness for me

The problem with @JC220 is that he has gotten radically sidetracked by pesky W140 models, door closing pumps and over-complicated electronics. Shiny objects and all that...
.

W220s too - just sayin... I don't discriminate as long as it has no less than 8 cylinders and a 3 pointed star ill be after it How did you know about my soft close pump fetish??

Quite grumpy this AM. The warm misfire is back. I've had the caps and insulators off several times in the last couple weeks without an improvement. Grasping at straws ATM. Last time I checked wires were fine. Cap and rotor are only a couple thousand miles old. No 'moisture' behind the insulators...

All suggestions to avoid the parts cannon welcome!

I do have the Pico to use, just need the time to get out there and use it

I hope its just old insulators for you! If they are original then they are due pretty much and you shouldt have to do it again.

I WILL also have a video put up soon on m119 ignition cap issues and my thoughts on an improvement for the system that costs $0 just some fettling. Just awating new Bosch insulators to arrive which should be late next week. The ignition system in my S500 is all mostly new but there is a factory design flaw in my opinion so maybe some of you might find that a litte interesting.

What model of Pico Scope do you have? I am interested to buy one myself actually. (There are 8x channel knock offs on ebay) Does it have only one high tension pickup I presume? I guess it doesn't matter you can scope a lead at a time.

Insulators require ruling out first me thinks and after that a fresh set of leads can't hurt any.

 

[a777fan]

Still here and still kickin. Still dealing with hot misfires. Leading candidate is now my plug/coil wires. More on that later.

but for now some good news! I FINALLY found a set of OE 16” 8-holes, via forum member @mercepor (thank you!). They safely traversed the ocean, and I picked them up from my refurbisher this afternoon. They look fantastic!
Here is a shot in the trunk of the 540.



these are the 7.5 7.0 inch items (ET46) for the pedestrian 124s

Plan is to do a full sportline refresh on the suspension and pop these on to complete the look!!!!

 

[Kridre]

7.5 inch? What ET it is? My 400E sportline arrived from factory with 8-holes 16x7 ET46 so I'm interested about the details.

 

[gsxr]

Make sure to document the Sportline conversion! These wheels are the cherry on top.

 

[a777fan]

7.5 inch? What ET it is? My 400E sportline arrived from factory with 8-holes 16x7 ET46 so I'm interested about the details.

Shnikes! You are absolutely correct. They are 7s not 7.5s (ET46) !! Original post corrected in 3..2..

 

[TerryA]

Still here and still kickin. Still dealing with hot misfires. Leading candidate is now my plug/coil wires. More on that later.

but for now some good news! I FINALLY found a set of OE 16” 8-holes, via forum member @mercepor (thank you!). They safely traversed the ocean, and I picked them up from my refurbisher this afternoon. They look fantastic!
Here is a shot in the trunk of the 540.

View attachment 114710

these are the 7.5 7.0 inch items (ET46) for the pedestrian 124s

Plan is to do a full sportline refresh on the suspension and pop these on to complete the look!!!!

Very Nice 777,

A good buy for you I hope. I would like to have a good original set like this. For my 93 500E of course.

I have my original 16" wheels but they were chromed and in pretty poor shape and need to be stripped and re-furbished to OE Silver. I think it would be easier to just find a good set for sale by a member. For now mine are just setting wrapped up on the side of the house.

 

[a777fan]

Very Nice 777,

A good buy for you I hope. I would like to have a good original set like this. For my 93 500E of course.

I have my original 16" wheels but they were chromed and in pretty poor shape and need to be stripped and re-furbished to OE Silver. I think it would be easier to just find a good set for sale by a member. For now mine are just setting wrapped up on the side of the house.

Thanks Terry!

Hopefully the 8” wide model which you can fit on to your 500 is a little easier to obtain. From my experience, the narrower pedestrian version is quite hard to come by if you want OE.

 

[northNH]

For future reference, as previously noted...
Italian aftermarket 7.5 x 16 ET40 with 215/55 Michelins, Sportlined suspension:

 

[gsxr]

For future reference, as previously noted...
Italian aftermarket 7.5 x 16 ET40 with 215/55 Michelins, Sportlined suspension:

Those are niiice. Do they use ball seat or cone seat lug bolts? Are these available new anywhere?

 

[Jlaa]

For future reference, as previously noted...
Italian aftermarket 7.5 x 16 ET40 with 215/55 Michelins, Sportlined suspension:

That ET+40 is very nice. The 6mm more poke compared to OE ET+46mm make a visual difference.

 

[Jlaa]

Those are niiice. Do they use ball seat or cone seat lug bolts? Are these available new anywhere?

Tirerack

https://www.tirerack.com/wheels/results.jsp?&autoMake=Mercedes-Benz&autoModel=300E+Sportline&autoYear=1993&autoModClar=

(Note the wrong image though that they are using for the w124 -- they confused the 124 with the 126).

https://www.tirerack.com/wheels/WheelCloseUpServlet?target=runWheelSearch&initialPartNumber=US4654S&wheelMake=ASA&wheelModel=Type%208&wheelFinish=Silver%20Painted&showRear=no&autoMake=Mercedes-Benz&autoModel=300E+Sportline&autoYear=1993&autoModClar=

 

[744Brillantsilber]

FYI: There also is a W210 wheel in the classic 8-hole design with 7,5x16 ET41.
Parts number A 210 401 07 02 and B6 6 47 0089

 

[a777fan]

For future reference, as previously noted...
Italian aftermarket 7.5 x 16 ET40 with 215/55 Michelins, Sportlined suspension:

No rubbing I assume with the extra poke? Looks great, and I can't wait!

 

[a777fan]

Well... today has been pretty interesting.

I started out troubleshooting the warm misfire issue. I had ordered a new plug wire set and went to work replacing them and getting them all in the appropriate trays. (Forgot what a pain that was.) Finished up that job, and was playing around with my scope (and noting that the warm misfire hadn't been totally eliminated with the new wires...grrr!!) When the blower motor kicked on.

That was odd for two reasons:
1. I had the Climate Control OFF
2. I was currently outside of the car, and no one else was with me

Mildly annoyed at first I was not all that concerned, until I opened the passenger side door to see SMOKE BILLOWING OUT OF THE VENTS AND CENTER CONSOLE AREA!!!!!

At that point, I went into full emergency mode. Turning off the car, mentally calculating the distance to the fire extinguisher I keep on the garage wall, and fumbling for a 13mm box end to disconnect the negative battery terminal. I got the battery disconnected, and the smoke coming out of the center console appeared to be dissipating. *phew*

Once I collected my wits, I started disassembling the upper center console, as this is where I had the most smoke coming from. This is what I found.



Yep. The good ole PBCU had enough apparently, and decided to toast itself. I kept disassembling... ya kno... for fun.



Serious WTF time. I don't think I have ever heard of this happening to another 124 before. Anyone else?

I am baffled as to how this happened without blowing a fuse. I obviously have more troubleshooting to do, but between this and the continuing warm idle misfire, I need an Uter break.

Good news though, I did find it very easy to disassemble the center console. This experience will come in very handy when its time to install the 'ASR off' switch in @TimL's car!!!

Oh... looking for a good condition late model PBCU. If you have one for sale, lemme know!!!

Now I'm going to go have a drink, or two.

 

[gsxr]

That is CRAZY! Glad you stopped it before anything worse happened.

Anyone know what that transistor does, which melted? Wild guessing either a bad blower regulator; or (less likely) shorted aux pump. Those are the only two major loads I can think of.

 

[TimL]

Well... today has been pretty interesting.

I started out troubleshooting the warm misfire issue. I had ordered a new plug wire set and went to work replacing them and getting them all in the appropriate trays. (Forgot what a pain that was.) Finished up that job, and was playing around with my scope (and noting that the warm misfire hadn't been totally eliminated with the new wires...grrr!!) When the blower motor kicked on.

That was odd for two reasons:
1. I had the Climate Control OFF
2. I was currently outside of the car, and no one else was with me

Mildly annoyed at first I was not all that concerned, until I opened the passenger side door to see SMOKE BILLOWING OUT OF THE VENTS AND CENTER CONSOLE AREA!!!!!

At that point, I went into full emergency mode. Turning off the car, mentally calculating the distance to the fire extinguisher I keep on the garage wall, and fumbling for a 13mm box end to disconnect the negative battery terminal. I got the battery disconnected, and the smoke coming out of the center console appeared to be dissipating. *phew*

Once I collected my wits, I started disassembling the upper center console, as this is where I had the most smoke coming from. This is what I found.

View attachment 114968View attachment 114969

Yep. The good ole PBCU had enough apparently, and decided to toast itself. I kept disassembling... ya kno... for fun.

View attachment 114970View attachment 114971View attachment 114972View attachment 114973View attachment 114974View attachment 114975

Serious WTF time. I don't think I have ever heard of this happening to another 124 before. Anyone else?

I am baffled as to how this happened without blowing a fuse. I obviously have more troubleshooting to do, but between this and the continuing warm idle misfire, I need an Uter break.

Good news though, I did find it very easy to disassemble the center console. This experience will come in very handy when its time to install the 'ASR off' switch in @TimL's car!!!

Oh... looking for a good condition late model PBCU. If you have one for sale, lemme know!!!

Now I'm going to go have a drink, or two.

Damn, so sorry to hear that Jon! Hope someone will have the part you need and hope that this isn’t something that a few PBR can’t solve!

 

[Jlaa]

Wow that is some serious transistor failure!!!

 

[gsxr]

I started out troubleshooting the warm misfire issue. I had ordered a new plug wire set and went to work replacing them and getting them all in the appropriate trays. (Forgot what a pain that was.) Finished up that job, and was playing around with my scope (and noting that the warm misfire hadn't been totally eliminated with the new wires...grrr!!)

Not to derail the HVAC PBU disaster, but... any word on what's going on with the misfire? Can you pin it down to one distributor or the other, or specific cylinders?

 

[TerryA]

@777,

Can that panel still be purchased from Mercedes? OR is it on the NLA list?

I’d buy a new one if it was available.

But maybe that’s just me.

 

[Joncf]

Well... today has been pretty interesting.

I started out troubleshooting the warm misfire issue. I had ordered a new plug wire set and went to work replacing them and getting them all in the appropriate trays. (Forgot what a pain that was.) Finished up that job, and was playing around with my scope (and noting that the warm misfire hadn't been totally eliminated with the new wires...grrr!!) When the blower motor kicked on.

That was odd for two reasons:
1. I had the Climate Control OFF
2. I was currently outside of the car, and no one else was with me

Mildly annoyed at first I was not all that concerned, until I opened the passenger side door to see SMOKE BILLOWING OUT OF THE VENTS AND CENTER CONSOLE AREA!!!!!

At that point, I went into full emergency mode. Turning off the car, mentally calculating the distance to the fire extinguisher I keep on the garage wall, and fumbling for a 13mm box end to disconnect the negative battery terminal. I got the battery disconnected, and the smoke coming out of the center console appeared to be dissipating. *phew*

Once I collected my wits, I started disassembling the upper center console, as this is where I had the most smoke coming from. This is what I found.

View attachment 114968View attachment 114969

Yep. The good ole PBCU had enough apparently, and decided to toast itself. I kept disassembling... ya kno... for fun.

View attachment 114970View attachment 114971View attachment 114972View attachment 114973View attachment 114974View attachment 114975

Serious WTF time. I don't think I have ever heard of this happening to another 124 before. Anyone else?

I am baffled as to how this happened without blowing a fuse. I obviously have more troubleshooting to do, but between this and the continuing warm idle misfire, I need an Uter break.

Good news though, I did find it very easy to disassemble the center console. This experience will come in very handy when its time to install the 'ASR off' switch in @TimL's car!!!

Oh... looking for a good condition late model PBCU. If you have one for sale, lemme know!!!

Now I'm going to go have a drink, or two.

THAT IS INSANE! Glad you’re alright and that there was no collateral damage. I’ve never heard of this happening. Hopefully it was just something as simple as the blower resistor as @gsxr has suggested.

 

[Gatorblue92]

Well... today has been pretty interesting.

I started out troubleshooting the warm misfire issue. I had ordered a new plug wire set and went to work replacing them and getting them all in the appropriate trays. (Forgot what a pain that was.) Finished up that job, and was playing around with my scope (and noting that the warm misfire hadn't been totally eliminated with the new wires...grrr!!) When the blower motor kicked on.

That was odd for two reasons:
1. I had the Climate Control OFF
2. I was currently outside of the car, and no one else was with me

Mildly annoyed at first I was not all that concerned, until I opened the passenger side door to see SMOKE BILLOWING OUT OF THE VENTS AND CENTER CONSOLE AREA!!!!!

At that point, I went into full emergency mode. Turning off the car, mentally calculating the distance to the fire extinguisher I keep on the garage wall, and fumbling for a 13mm box end to disconnect the negative battery terminal. I got the battery disconnected, and the smoke coming out of the center console appeared to be dissipating. *phew*

Once I collected my wits, I started disassembling the upper center console, as this is where I had the most smoke coming from. This is what I found.

View attachment 114968View attachment 114969

Yep. The good ole PBCU had enough apparently, and decided to toast itself. I kept disassembling... ya kno... for fun.

View attachment 114970View attachment 114971View attachment 114972View attachment 114973View attachment 114974View attachment 114975

Serious WTF time. I don't think I have ever heard of this happening to another 124 before. Anyone else?

I am baffled as to how this happened without blowing a fuse. I obviously have more troubleshooting to do, but between this and the continuing warm idle misfire, I need an Uter break.

Good news though, I did find it very easy to disassemble the center console. This experience will come in very handy when its time to install the 'ASR off' switch in @TimL's car!!!

Oh... looking for a good condition late model PBCU. If you have one for sale, lemme know!!!

Now I'm going to go have a drink, or two.

I've seen one like this in a junkyard before but never heard of it happening to anyone on the forums. Glad you were able to get it under control before any significant damages.

 

[gerryvz]

I have a few PBUs, and I'm happy to send you one at no cost and at my postage expense. I'll take some photos and post them to be sure it will work for you.

By the way, re:the warm misfire, have you replaced the coils?

Cheers,
Gerry

 

[a777fan]

Thanks all! Yep, also glad I was there when it happened, and I was parked safely at home in my driveway. Would have been a mess if I was out and about.

@gsxr - No firm diagnosis on the miss yet. I do have some scope 'footage' to go back through though, so more in the coming days.

@gerryvz Thanks for the offer honch! I'd gladly take you up on it if you have a late model PBU kicking around and didn't have an immediate need for it. I'll insist on at least paying for shipping however! According to ISPPI either A1248303385 or A1248303185 will work. (not clear what the difference is). Additionally - on the misfire yes, both coils are now new.

I'm still struggling with the cause of this. To clear the air, the car has no wiring modifications to it. No stereo tomfoolery or anything like that. At this point I think I have to assume the carnage is the result of another problem in the system and not the cause. @gsxr - I concur with your analysis, looks like the blower motor regulator is the only substantive 'load' on the PBU. I do see reference to a 400E/500E aux fan in the wiring diagrams, but it would appear that this is only a signal output, consumed by the aux fan relay, and not a 'load'. As such, it seems like the regulator is a prime suspect... especially since this whole episode initially caught my attention with the blower motor kicking on. Still thinking on this, and thoughts/opinions welcome. Also wondering if there is a way to test the regulator without the possibility of burning the car down.

 

[a777fan]

@777,

Can that panel still be purchased from Mercedes? OR is it on the NLA list?

I’d buy a new one if it was available.

But maybe that’s just me.

Terry, yep they are NLA.

 

[Kyiv]

Anyone who can rely on some electrical experience (@Jlaa ?) speculate if this was a more or less guaranteed fire it not caught right away, or, more-likely-than-not after some melting the circle would have been broken and burning would stop? Mine and my child's bedrooms are right above the garage... Effin' very scary.

 

[Jlaa]

Hiya @kiev, I'm not sure I have enough real-world experience to say --- I'm a theory guy..... I'm the guy that could do well on all my undergrad Electrical Engineering exams but then have no clue once I get into the lab!

I think the main problem is fuel materials for such a fledgling electrical fire. Coatings on components like capacitors and resistors and diodes and what not can be fuel, but there's not a lot of it and it won't burn for a long time. However, the PCB board itself is made of epoxy and it burns --- and relatively speaking there is a lot of it to act as a fuel. There are some PCBs which are flame rated by Underwriters Laboratories (I have no idea though about automotive components) but even then, virtually all materials will burn if the temperature is high enough, and it looks like the temperature was high enough to cause the epoxy PCB to burn ----- and the photos show that there was still plenty of fuel to make a big fire.

 

[Jlaa]

@a777fan ---

Looking through the intrawebz, it looks like this same/similar thing happnened to "alphadeltaromeo" and his 95 E300E in 2010 --- and he posted pictures of the melted PCB from his PBCU:





The thread doesn't talk about the root cause, but it might provide some clues ..... (alphadeltaromeo was fussing with his monovalve at the same time...) Smoke comes from the dash! - PeachParts Mercedes-Benz Forum

ALSO --- look here --- HELP!! Smoked my second CCU control... - PeachParts Mercedes-Benz Forum . Look at post #7 and post #12. These are stories of melted / burned PBCUs from w126s (which I presume to be a similar design --- @gerryvz?) ... anyways their experiences point to dead monovalves / stalled electric motor / super-high-current --> melting??

Again I have no idea if that is the culprit, but maybe this can point you down the right path once you have a clear mind and are willing to work on Uter again.