OWNER a777fan (E420)

[gsxr]

The only 3 things I can think of with any real load are the blower regulator, aux pump, and monovalve. I *think* all three are directly controlled by the PBU, i.e. not through a relay like the auxiliary fans ahead of the condenser. But even the blower regulator should only be a light load, as it's a control signal... the regulator acts sort of like a relay in that it controls high current (25A+) from a low current input.

I'd check the monovalve and aux pump for grins. They are easy to test with an ohm meter and/or applying test voltage to see what happens, with the harness unplugged. The blower regulator is a bit more complicated to test.

 

[gerryvz]

Hey Triple Trouble,

Here is a PBU from my parts stock. It’s from a 1995 E320 wagon, and I got it in August 2013. Seems to be all there.

MB part number 124 830 33 85

Please tell me where to send it, and it is yours, gratis. I can get it out to you today via Priority Mail if I can get your mailing address via PM.

Cheers,
Gerry

 

[a777fan]

Hey Triple Trouble,

Here is a PBU from my parts stock. It’s from a 1995 E320 wagon, and I got it in August 2013. Seems to be all there.

MB part number 124 830 33 85

Please tell me where to send it, and it is yours, gratis. I can get it out to you today via Priority Mail if I can get your mailing address via PM.

Cheers,
Gerry

View attachment 115099

View attachment 115093View attachment 115094View attachment 115095View attachment 115096View attachment 115097View attachment 115098

Gerry, thank you thank you thank you! Will follow up with PM.

 

[a777fan]

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. ☹

@kiev, I am fairly certain this failure mode is limited to when the key is in the 'Run' or 'Start' position. The smoke started to dissipate following me turning the key to the 'OFF' position. I did disconnect the battery as an extra safety measure, so I cannot be 100% certain of this, but it is my current (no pun intended) theory.

 

[a777fan]

@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:

View attachment 115078
View attachment 115080
View attachment 115079

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. ☹

Unbelievable @Jlaa! Thank you very much for this. It looks to be exactly the same failure mode. The monovalve eh? Hmm... I am completely unfamiliar with that component, and will need to dig in more.

 

[gsxr]

Unbelievable @Jlaa! Thank you very much for this. It looks to be exactly the same failure mode. The monovalve eh? Hmm... I am completely unfamiliar with that component, and will need to dig in more.

Monovalve is the heater control valve, located behind the CAN box. There is an early and late style, NOT interchangeable. Cutoff point is mid-1994 production, and the EPC has the incorrect break point. You have to visually confirm which type is on your car.

It's called "monovalve" as it's a single on/off valve that controls all coolant flow through the heater core. Euro models with manual climate control offer different temperature settings for driver and passenger, these models have a "duovalve" with two solenoids / two valves, one for each half of the heater core.

<--- Car-B-Que

 

[a777fan]

Thanks Dave.

Sounds very similar to the system that BMW uses on the E34. I'll have to see if I can find anything about the spec of this valve to see if I can figure out if its bad. I assume its a simple coil driven device that should have a very specific resistance associated with it?

 

[gerryvz]

@Jlaa -- Yes, the PBUs from the 126 and 124 are of a functionally similar design, but physically they are different (the 124 design is taller to accommodate the center console switches). But they work on the same principle, yes.

 

[gsxr]

. I assume its a simple coil driven device that should have a very specific resistance associated with it?

Correct - it is a simple coil. Normal resistance is 12-15 ohms. I had one almost shorted, ~1 ohm, but the PBU has a safety and the only result was max heat all the time (valve never closed). Now, if the built-in safety on the PBU failed... hmm....

Early type monovalve:


Late-style monovalve has an extra port and is taller:

 

[Jlaa]

Correct - it is a simple coil. Normal resistance is 12-15 ohms. I had one almost shorted, ~1 ohm, but the PBU has a safety and the only result was max heat all the time (valve never closed). Now, if the built-in safety on the PBU failed... hmm....

Hi @gsxr -- what is the "built in safety mechanism" for overcurrent in the PBU that protects from:
- failed monovalve
- failed auxiliary coolant pump
? Just curious.

(below is some fruitparts commentary on failure modes in a w123)



I vaguely remember some years ago I had a lot of clicking in the dashboard of E500E in city driving at super low RPMs during cold weather when my heater was on. The thought at the time (vaguely remembering) was that it was symptomatic of a failed auxiliary coolant pump (located next to monovalve) and the clicking was some kind of relay cycling on/off trying to get the coolant pump going to get more heat into the system ....... but that the clicking was some built in protection circuitry that would cycle on/off to prevent the climate control system from melting itself since the aux coolant pump wasn't cooperating (stalled DC motor = super high current).

I replaced the aux coolant pump with a new Bosch unit (IIRC I got it on Amazon too) and the clicking went away. In hindsight I wish I had tested the old coolant pump to determine if it had actually failed and what the failure mode was. :-(

 

[gsxr]

Jlaa, I honestly don't know exactly. I remember hearing something from other kids on the playground about the PBU curling into a fetal position when there's a short in the aux pump (and possibly monovalve). When this happens, other functions may be affected, i.e. not work properly. In some cases unplugging the affected item may let the system work normally again, except for the disconnected component.

Clicking sounds are usually from the 7-port vacuum manifold, on the passenger side of the heater box, behind the airbag. I know from experience that if the aux pump current exceeds whatever amount the PBU likes to see, it can cause the PBU to not trigger the appropriate signals to the vacuum manifold. And possibly clicky noises.

Typical failure mode of the aux pump is worn brushes, and it simply does not run, unless smacked with a tool or rock... then it jumps to life. That one time. And then after it stops, it likely needs to be whacked again. People in warm climates may never noticed if the aux pump isn't working, but in cold climates, you'll notice it at long stoplights. I think in this failure mode it's electrically open, not shorted?

 

[a777fan]

Ok, I did a little more research this afternoon and some digging in the car, and I think I now have some answers.

@Jlaa to answer your question about how the Mono Valve and Coolant Pump are 'protected', I took a look at the 124 ETM.

Here is the Power/Ground Schematic for production from 1987 onward.



Note, I have annotated this with brown lines that represent the fact that the Switchover Valve Unit (Controls the Air flappies), the Mono Valve and the Coolant Pump are all grounded through the PBU. This will become clearer in the next figure. But for now @Jlaa and @gsxr note that all 4 of these items get their power from Fuse 7. So that is one question down.

On to the next figure which gives us the pin-out for the PBU. We can use that to determine how all four of these items work together.



I have also annotated this figure to show the power (red) and grounds (brown) of interest. You can see that conveniently (and as noted on the previous figure as well) that the PBU, the Monovalve, the Switchover valve unit and the Coolant Pump all get their power from one source. This makes troubleshooting all the components pretty easy, as you can check the various resistances of ALL of the components right at the X1 and X2 connectors! So thats what I did. I got out my multi-meter and started checking. Here are the results:



Check out that Mono-valve number!!! I think it's pretty shot. Do you all concur?

I also have questions about the Coolant Pump Number. It seems high. Does anyone know what the spec is?

Side note - I also ohmed out the Aspiration Blower. No need to hunt around under the dash. Referencing Figure 2 above, just disconnect the connector from the Mono valve, find the pin with the black/purple wires, and then check the resistance from there to ground. I got 5.1 ohms, which also seems high. Also looking for confirmation of the spec on that one.

So... the Mono-valve is essentially shorted completely out at this point. All that current with nothing to stand in the way pumping right into the poor little PBU. I assume the blower motor kicking on was simply an artifact of the control module melting/catching on fire. That still doesn't explain why the fuse that controls all of these components did not blow. For that, I did a little more digging and comparing. First.. remember the ETM Power distribution figure? Let me remind you what it said, zooming in:


Fuse 7 - 8 Amps. Cool. Lets go over to the fuse box and see what it looks like...



White is 8 amps.... Red is 16... WTF?!

Did I goof up when I installed my non-metallic aluminum fuse set?!?! Let's check:



NOPE! The car calls for a 16 Amp fuse in this location!!! So... WTF!?!?

My guess is that somewhere along the lines of the W124 lineage, new items kept getting added on to Fuse 7, which required a bump from 8 amps to 16. Did they do all their homework when they made that change? I do not know. All I know is that I have a 16 amp fuse in my fuse box, a broken Mono-Valve and an absolutely BBQ'ed PBU!

Once I have put everything back (new Mono etc), I plan on making Fuse 7 an 8 amper, and see how that goes. Maybe it will be enough, maybe it will immediately blow. If I am forced into a 16 amp fuse in that location, I will certainly be adding a check of the Mono-valve resistance to my annual maintenance tasks.

Anyway, it was an interesting evening, so I wanted to share with you guys. It feels somewhat good to have some certainty behind the cause of all this. Let me know your thoughts and observations. If I were you, I'd go check the resistance of my mono valve ASAP!

Oh... btw looks like i have the 'newer' Monovalve

 

[Kyiv]

@a777fan, absolutely awesome post!

 

[Jlaa]

Wow @a777fan. That is some serious sleuthing! Bravo! Way to make lemonade out of lemons. 0.9 ohms across the monovalve means the PBU is sinking >13amps of current through the PBU!

Correct - [The monovalve] is a simple coil. Normal resistance is 12-15 ohms. I had one almost shorted, ~1 ohm, but the PBU has a safety and the only result was max heat all the time (valve never closed). Now, if the built-in safety on the PBU failed... hmm....

View attachment 115129

Check out that Mono-valve number!!! I think it's pretty shot. Do you all concur?

I happen to have a spare monovalve on the shelf in my parts hoard and I measured the resistance across the terminals. See pictures below --- Right around 14 ohms. I think replacing your monovalve is wise.



I'm sorry that I don't have a spare aux coolant pump on the shelf to measure either .... but I note that 17 ohms is close to 14 ohms of the monovalve.

Regarding the fuse stuff ---- Yikes! I see what you mean about the diagrams saying 8 amps for fuse 7 but the car has a 16 amp fuse in that location. I confirmed that my car is also the same (16amp). Page 110/1 of the ETM does shows 16 amps for fuse 7 for 1990+ cars ....


And even for 1986 gasoline cars, the ETM shows on page 109/1 that Fuse 7 is a 16 amp fuse ....



However page 105/1 does show fuse 7 as an EIGHT AMP FUSE for Diesel cars.....



Such a mystery!!!

 

[a777fan]

Wow @a777fan. That is some serious sleuthing! Bravo! Way to make lemonade out of lemons. 0.9 ohms across the monovalve means the PBU is sinking >13amps of current through the PBU!




I happen to have a spare monovalve on the shelf in my parts hoard and I measured the resistance across the terminals. See pictures below --- Right around 14 ohms. I think replacing your monovalve is wise.

View attachment 115137 View attachment 115138 View attachment 115139 View attachment 115140 View attachment 115141

I'm sorry that I don't have a spare aux coolant pump on the shelf to measure either .... but I note that 17 ohms is close to 14 ohms of the monovalve.

Regarding the fuse stuff ---- Yikes! I see what you mean about the diagrams saying 8 amps for fuse 7 but the car has a 16 amp fuse in that location. I confirmed that my car is also the same (16amp). Page 110/1 of the ETM does shows 16 amps for fuse 7 for 1990+ cars ....
View attachment 115142

And even for 1986 gasoline cars, the ETM shows on page 109/1 that Fuse 7 is a 16 amp fuse ....

View attachment 115143

However page 105/1 does show fuse 7 as an EIGHT AMP FUSE for Diesel cars.....

View attachment 115144

Such a mystery!!!

Thanks for those specs @Jlaa! I appreciate you going out to the garage to check for me.
I will note that a new monovalve is ~400 dollars. This is for the new style that I have. The older style is only ~100. So bummer there.
Additionally good detective work on the remainder of the ETM! One of my pet peeves about documentation is when you have one piece of info embedded in multiple locations. So hard to keep track of all of them and keep them correct, as seems to be the case here. Who knows what amperage was intended for this location on the V8 powered cars. I’d say that the little card that sits in the fuse box probably has the highest chance of being right, but I also doubt that this is an intended failure mode for the system.
For example- as you correctly pointed out, with an 8amp fuse, this issue would have snuffed itself out once the resistance of the valve dropped below 1.5 ohms and the current exceeded 8 amps. Would that have turned this tinderbox into a mild annoyance? I dunno! I hope to never find out.

 

[gsxr]

You are sort of lucky. The early style monorail monovalve is NLA.

Late style is available, $470 MSRP, lowest price I know of is Ed Hicks in TX at ~$260. If only we could get them to offer a shipping discount...

1992-1995 Mercedes-Benz HVAC Heater Control Valve 001-830-25-84 | OEM Mercedes Benz Parts

1992-1995 Mercedes-Benz HVAC Heater Control Valve 001-830-25-84

parts.edhicksimports.com

 

[Jlaa]

Once I have put everything back (new Mono etc), I plan on making Fuse 7 an 8 amper, and see how that goes. Maybe it will be enough, maybe it will immediately blow. If I am forced into a 16 amp fuse in that location, I will certainly be adding a check of the Mono-valve resistance to my annual maintenance

If the 8 amp fuse in position 7 is not to your liking, you could also consider wiring a discrete fuse of appropriate value (2 amps maybe?) under the hood, directly on the contact of the monovalve connector. Perhaps find the male/female ends for these MB connectors and make it super nice?

 

[gsxr]

If the 8 amp fuse in position 7 is not to your liking, you could also consider wiring a discrete fuse of appropriate value (2 amps maybe?) under the hood, directly on the contact of the monovalve connector. Perhaps find the male/female ends for these MB connectors and make it super nice?

Yep... same for the aux pump, with appropriate fuse size.

Strange that my '95 E420 had an identical monovalve failure (1 ohm) but the only result was max heat all the time. No smoke show. Drove it like that for a year (clamped off hose in summer) before eventually locating a good used monovalve, as I was too cheap to shell out for new.

 

[a777fan]

If the 8 amp fuse in position 7 is not to your liking, you could also consider wiring a discrete fuse of appropriate value (2 amps maybe?) under the hood, directly on the contact of the monovalve connector. Perhaps find the male/female ends for these MB connectors and make it super nice?

View attachment 115231

I had already started contemplating that! Great minds think alike

 

[a777fan]

Yep... same for the aux pump, with appropriate fuse size.

Strange that my '95 E420 had an identical monovalve failure (1 ohm) but the only result was max heat all the time. No smoke show. Drove it like that for a year (clamped off hose in summer) before eventually locating a good used monovalve, as I was too cheap to shell out for new.

Yes, very odd!

I need some MB buffs to help me out here with my history... Wasn't there a PN change to the PBU around 1992? I'm wondering if it was re-designed with a safety (as you had previously mentioned @gsxr) in order to upgrade Fuse 7 to 16 A from 8. Perhaps in my unit that 'safety' has failed? Purely speculation of course. Not sure how one would test this theory.

 

[a777fan]

You are sort of lucky. The early style monorail monovalve is NLA.

Late style is available, $470 MSRP, lowest price I know of is Ed Hicks in TX at ~$260. If only we could get them to offer a shipping discount...

1992-1995 Mercedes-Benz HVAC Heater Control Valve 001-830-25-84 | OEM Mercedes Benz Parts

1992-1995 Mercedes-Benz HVAC Heater Control Valve 001-830-25-84

parts.edhicksimports.com

Thanks Dave! Ordered and its on its way. Even with shipping, that is a nice savings

And yes... discounted MSRP is always better that un-obtainium

 

[gerryvz]

Hey Trip, any updates on how things are coming along with the ACC system on your car?

 

[gsxr]

BTW, I found my spare auxiliary pump. It's 10-11 ohms.

 

[a777fan]

Nothing to report at the moment. I am still awaiting the monovalve from CC MB. Hat tip to @gsxr

Looking forward to putting it in, along with the PBU that you generously provided @gerryvz! But while I wait, we decided to do a socially distanced national park vacation down to Arches and Canyonlands NP!

If you haven’t been, you really need to go. Pictures don’t do it justice.

 

[gsxr]

Arches and Candyland are incredible. Looks like you had perfect weather too. I see you hiked up to Delicate Arch! Worth the effort, eh? I assume you checked out Needles too. If you have time, stop by Dead Horse Point (across the street from Arches). One of these days we want to go back for another week or more...

 

[TerryA]

Nothing to report at the moment. I am still awaiting the monovalve from CC MB. Hat tip to @gsxr

Looking forward to putting it in, along with the PBU that you generously provided @gerryvz! But while I wait, we decided to do a socially distanced national park vacation down to Arches and Canyonlands NP!

If you haven’t been, you really need to go. Pictures don’t do it justice.

Very Nice Jon,

Been there done that back in the 80's I think. Really beautiful. I probably have those same pics in 35 mm but I would have to find them in one of my Wife's photo scrap books.

After cruising for the last few years, I wouldn't step foot on a cruise ship for a while. It's to easy to catch anything on a ship. Covid would be a disaster.

I think a driving trip will be are next vacation.
Probably the only safe way until they get this Covid under control.

lol

 

[Trae]

Did you ever get to the bottom of "missing when warm" syndrome?

I am experiencing the same symptoms in the 92' 500E.
New coils, Beru caps, OE rotors, new Beru wires (checked for 2,000 ohms), new F8DC4 spark plugs gapped to 1mm. and properly torqued.

Runs great when cold/cool. As soon as it is at operating temp., an intermittent miss starts.
Seems to disappear when I floor it! Then returns when normal driving. Runs smooth for a moment, then misses for a while, followed by more smooth running, then misses. Don't know where to go next.

 

[a777fan]

Did you ever get to the bottom of "missing when warm" syndrome?

I am experiencing the same symptoms in the 92' 500E.
New coils, Beru caps, OE rotors, new Beru wires (checked for 2,000 ohms), new F8DC4 spark plugs gapped to 1mm. and properly torqued.

Runs great when cold/cool. As soon as it is at operating temp., an intermittent miss starts.
Seems to disappear when I floor it! Then returns when normal driving. Runs smooth for a moment, then misses for a while, followed by more smooth running, then misses. Don't know where to go next.

Hey trae!

Funny you should ask. I spent this afternoon with Üter, and part of what I was doing was continuing to troubleshoot my warm miss.

I still have the miss, and have replaced the following so far:

Insulators
Rotors
Caps
Plug wires
Coils

I have scoped with my Pico, but have not come to any specific conclusions yet from the data as of yet. The miss is definitely in the secondary ignition, but it moves around to different cylinders when it occurs. I plan to spend some additional time tomorrow and will report back if I have any findings.

 

[Joncf]

Hey trae!

Funny you should ask. I spent this afternoon with Üter, and part of what I was doing was continuing to troubleshoot my warm miss.

I still have the miss, and have replaced the following so far:

Insulators
Rotors
Caps
Plug wires
Coils

I have scoped with my Pico, but have not come to any specific conclusions yet from the data as of yet. The miss is definitely in the secondary ignition, but it moves around to different cylinders when it occurs. I plan to spend some additional time tomorrow and will report back if I have any findings.

Your plugs are gapped to 1mm?

 

[a777fan]

Your plugs are gapped to 1mm?

Indeed

 

[Kyiv]

Could it be an out of spec, but still performing, LH module?

 

[a777fan]

I’ll have to edit them and post, but the scopes I have of the primary ignition circuit clearly show a dead short to ground, outside the cylinder that moves from cylinder to cylinder randomly. This leads me to think its a rotor/cap/insulator issue....

 

[Trae]

I replaced, faulty out of the box, Bremi rotors with OE. Still a miss. Planning to replace brand new Bosch caps with, made in Germany, OE caps today.

 

[gerryvz]

I think you need to bring your car into a shop that has a Sun scope. That way they can see electrically what is happening in each of the cylinders, and determine which cylinder (or cylinders) are acting up. Once this is pinpointed, then you can hone in on the components that could be bad for that cylinder(s).

There are a couple of good shops in the Seattle area -- have you spoken to Steve Geyer at SG Motorsports? He's a member here, but I'd call him or email him and see if he can assist. He knows these cars well.

The one time I had a dead short to ground was on my 560SEC, and it ended up being one of the insulators at the end of one of the plug wires. It was shorting to the cylinder head. Replaced the insulator (I think it was a $12 part at the time) and I was on my way. The Sun oscilloscope pinpointed the cylinder in mere seconds.

 

[gsxr]

I’ll have to edit them and post, but the scopes I have of the primary ignition circuit clearly show a dead short to ground, outside the cylinder that moves from cylinder to cylinder randomly. This leads me to think its a rotor/cap/insulator issue....

Jon, can you pin it down to 1 distributor cap? Or does it jump around to cylinders from both caps?

If it's only 1 cap... you could swap the cap/rotor and see if the problem follows those components.

 

[Trae]

In my zeal to throw parts at this car, still have to not solved the problem. If anything made it worse today when I replaced Bosch with Beru caps.

Been through Bremi (no good), Bocsh, Beru, and OE caps and rotors. So, I can, at least , rule them out.

 

[Trae]

May be oscilloscope time.

 

[a777fan]

Ok... back with data! And I think I was able to identify my culprit, at least for this round of the warm misfire mystery...

Let's start off with some basics. I was monitoring ignition coil Primary Voltage for this test. Here is what a 'good' Primary voltage trace looks like:



I won't got into detail here, as there are PLENTY of good tutorials and info on the interwebs that will walk you through the shape and the various characteristics of this curve. There is a TON of information about how this specific cylinder is performing buried in this picture, so if you are curious to know more, I highly encourage you to head over to google and youtube to learn more.

Above is a 'good' ignition event. Here is a 'bad' event, associated with a misfire.



See the difference? Not all 'misfires' you may run across will look like this. But this specific signature hints that there is somewhere outside the cylinder where the spark is running to ground BEFORE it makes its way to the plug. In all the scope monitoring of warm misfires on my E420, this is the signature that ALWAYS is associated with it. They ALL look like this.

Ok, so what did I do today... I have a 4 channel Picoscope. For this test, I monitored the Primary Voltage on each Ignition Coil (both of them Red and Blue signals), and the Injector voltage on Cylinder 5 (Green signal). I utilized the Cylinder 5 Injector voltage as a 'trigger' to allow me to make sense of which Primary Voltage 'spike' belonged to each cylinder. I hooked up the scope, and began to monitor the ignition events in a 'parade' style view. It didn't take long for the engine to start missing. This is what I saw (I have annotated the picture with the specific cylinder for each event:


As you can see, there are several misfire events coming from the T1/1 coil signal. The misfires were not always on the same cylinders as shown above, but were ALWAYS on the T1/1 trace. This is the coil that drives the passenger side bank distributor. All of my misfires were coming from THAT coil! This is very exciting, as it obviously allows for troubleshooting. At this point I knew there was either:

1. An issue with the coil (unlikely, as it was just replaced)
2. An issue with the passenger side distributor cap (also unlikely, as it was also just replaced)
3. An issue with the rotor (Hmmm.... I have replaced these, but... they are the oldest 'new' part)
4. An issue with the insulator (Unlikely... as these are also new and in good visual order)
5. An issue with the king lead to that distributor from the T1/1 coil (unlikely as this is also new)
6. An issue with each individual spark plug wire from this specific distributor cap (unlikely due to the number of failures to realize this failure mode)

So.. with that list above, I decided to swap the rotors between the passenger and drivers side bank. I fired it up again, and this is what I saw:



Lookie... lookie. The misfires MOVED with the rotor. Hot damn.

I am disappointed to see this however. These rotors are only slightly used. I replaced them in 2018, and they were OE MB products from our very own Tom Hanson. Sooo.. based on this, I will be buying a replacement rotor. I'll then re-test to see if this has fixed the issue.

I was going to attach my Picoscope files here for you to download and play around with if you are interested, but they are too large to upload. Let me know if you'd like to take a look and I can email them to you. The scope software can be downloaded for free from Picoscope here: PicoScope oscilloscope software and PicoLog data logging software

 

[gerryvz]

Good detective work, Triple Trouble!

I would contact Tom and get a free replacement with MB’s two-year parts warranty.

 

[Trae]

Unbelievable! I am experiencing almost identical symptoms. Had new Bosch cap and rotors. Swapped rotors to OE. No change. Swapped caps to Beru and made things worse last night. Now the misfire occurs even when cold.

Going back to the Bosch caps today and will continue to diagnose.

Very impressive Jon!

 

[nocfn]

The not so obvious message here is to hoard your replaced parts too with proper labeling as to location with install and removal dates so that one can be in position to swap them in when new stuff begins to fail. (humor intended)

Good work, and a great benefit of BTDT for the field, thank you!

 

[gerryvz]

It seems that several people have had defective ignition components right out of the box. It just goes to show that just because something is "new" is not a guarantee that it is functioning 100% correctly. Kudos for using a methodical approach to testing, and [hopefully] finding the culprit.

 

[nocfn]

^^^^^

here here!

 

[Trae]

I wish I were a better diagnostician instead of throwing parts at cars as it would save $$$, however, the side benefit is a parts stash that continues to grow to the consternation of my wife. I now have many caps and rotors from many manufacturers.

 

[a777fan]

I wish I were a better diagnostician instead of throwing parts at cars as it would save $$$, however, the side benefit is a parts stash that continues to grow to the consternation of my wife. I now have many caps and rotors from many manufacturers.

Hehe... don't feel too bad Trae. I HAVE all that diagnostic equipment and STILL replaced just about everything (As you can see from my list above).

Amazing tools not a good mechanic makes...

 

[a777fan]

Good detective work, Triple Trouble!

I would contact Tom and get a free replacement with MB’s two-year parts warranty.

Unfortunately I purchased said rotor in May of 2018. 29.5 months ago!

Off to the parts bin I go!!!

 

[Trae]

Strangest thing. After replacing every electrical component, car still missed for 10 miles to the grocery store. Got back in the car and drove the next 10 miles operating normally in all regimes. Smooth as butter with NO miss.

After arriving home, let car sit for 3 minutes. Then, when started the miss returned!?

 

[a777fan]

Strangest thing. After replacing every electrical component, car still missed for 10 miles to the grocery store. Got back in the car and drove the next 10 miles operating normally in all regimes. Smooth as butter with NO miss.

After arriving home, let car sit for 3 minutes. Then, when started the miss returned!?

After looking at data over a couple of 'experiments' (not just the one example I recently posted about), I wonder if these systems have not one but several inherent 'weak points' that result in off nominal behavior in different environmental scenarios. Your example above doesn't have quantitative data associated with it, but as you indicate, its hard to stich a logical thought process through the qualitative data you do have.

 

[Trae]

Plugs, wires, caps, rotors, insulators, and coils all new.

Next upstream electrical is to swap EZLs, Egas, and LH modules to see if there's a difference.

Wondering if any of those could be responsible for intermittent misfires?

 

[gsxr]

Plugs, wires, caps, rotors, insulators, and coils all new.

Next upstream electrical is to swap EZLs, Egas, and LH modules to see if there's a difference.

Wondering if any of those could be responsible for intermittent misfires?

It's highly unlikely any of those would cause ignition misfires. But you are running low on options without either a 'scope, OR at least an SDS. Trae, if you have SDS, see if you can pull live data from the EZL/DI where it shows the ignition voltages for all 8 cylinders. When the misfire occurs, the voltages will double from the normal 30-35 up to ~70 or so. This will tell you which cylinders are the culprits.