What do you think is going on here...


How do we know "harness" is doing this?

Any good way to troubleshoot cause ??

Is this all about "Coil-7" only?

 

I don't think so, considering cylinder 7 isn't the only cylinder misfiring. There's also very minor misfires on 6 and 8, albeit not nearly as many as 7. Xentry alternator tests are still failing across 2 new alts.

So definitely electrical gremlins beyond coil 7.

 

don't shoot in the dark - I really don't see harness itself being guilty for all that chaos.
Also as you point out it really is not bad "coil-7 signal" either.


> Cancel low voltage:
Let's center the issue back onto bad voltage control which you have confirmation ALT is not guilty of.

Here...
experiment simply unplugging "BATT-LIN" and see if misfires are improved...
If yes then reboot + float main battery.

I have not tested "Batt-LIN" vs. crazy ECU networking which you seem to have.

I don't how much BATT-LIN guarantees ok voltage given the ALT <--> LIN <--> ECU is still stock control.

Read chassis voltage is made reliable or not above 14Volts.

The only reason to consider BATT-LIN over ALT-LIN is it's much faster on and off for testing purposes. ALT-LIN still preferred way.


Then concider next step to address issues... hopefully not a blind shot.

 

Been awhile since I posted an update. It took a few weeks to sort out the ECU due to an cloning issue with the first vendor. First we tried a software update. No results. Then we tried swapping in a good ECU cloned from my existing. No results. So that seems to be ruled out. However before the ECU's were messed with, the alternator seems to have sorted itself out. As in, it's passing the Xentry tests now. Although I think it's unclear at the moment if the ECU had any effect on that. Either way, the misfires are still there along with the hesitation feeling.

The specialist it's at right now is at somewhat of a loss. They mentioned they checked out the harness. In terms of what exactly they did, I'm not sure but I trust their judgement. Open to recommendations. My baby hasn't been properly on the road for months and definitely missing her. Especially with the nice weather here right now

The specialist mentioned he did see some voltage discrepancies going to the misfiring coil packs, but I don't have more info beyond that. How that isn't considered an issue with the harness, I'm not sure. Waiting to get more info on that.

 

suggestion 1:

Sell the car - lots of suggestions have been offered up, you did due diligence

suggestion 2:

Good luck - hope you find it - otherwise maybe live the the hesitation? You don't seem to want to sell this car

 

I don't want to sell it because I'd be at a huge loss. The only way I can make this headache somewhat worth it is if I fix the issue and actually enjoy it for years. I'm not sure what selling would accomplish aside from making this all pointless.

Unless I've missed something, I think I've addressed all the suggestions. The only thing left at this point, as far as I can tell, is potentially a wiring issue which is being investigated next. I don't think anything is unfixable. Yes things can be not worth it to fix, but this is. Considering once this is addressed, this should be one of the cleanest M156 W212's on paper with all the work I've done.

 

> RECAP:
New coils+ plugs (boots?)
New injectors
New Lambda
New ALTernatorS... 15.2Volts
GND circuits were checked
New ECU + firmware update

> Outcome:
misfirings Cyl. 7 + (6+8).

Q: How is this not simply the stock lean misfires??
The only thing wrong are the cylinders random timings.

 

Work Performed to Date:

Engine (All OEM parts):

• Spark plugs, coil packs, fuel injectors - all cylinders
• All 4 O2 sensors (Bank 2 upstream replaced twice)
• Head bolts (updated revision)
• Camshaft adjusters rebuilt (63 Motorsports)
• Camshaft lifters/tappets
• Valve cover gaskets
• Crankcase vent valve
• Intake manifold resealed
• Throttle bodies cleaned
• MAF sensors cleaned
• Camshaft position sensor Bank 2
• Camshaft solenoid Bank 2

Other:

• Both batteries replaced
• Full transmission service with TCU reset
• Throttle pedal
• Rear driveshaft flex joint
• Alternator
• Radiator
• ECU
  
  And yes misfiring 6,7,8. But mostly just 7. Just a few on 6 and 8 last I saw.

 

I agree. The question is why. As far as I can tell, that wiring is the only thing that's left.

And going back through my messages with the current tech, he did mention he hasn't seen 6 and 8 misfiring in his tests since he's had it. And when looking at the input signal on a scope, the "signal didn't look quite right". Not completely sure what that means. Hopefully I'll find out soon enough because that's all we have to go off of right now.

 

just trying to help ...

-- I don't think you've had any fault reporting harness being high or low as seen with poor circuits.
-- I don't see a harness job bringing you peace.

When you were getting 15.2V, ALL your ECU /Engine GND were reported fixed + tested ok.

The coil signal of a misfiring cylinder can look slightly different than a normally fired mixture. Its harder to spark weak mixtures beyond lean.

You have a fresh ECU ignition drivers and new coils.

You have two separate HPFP pumps and essentially bank2 cyls are misfiring.... that doesn't land in bad harness territory unless known swamped by oil.
I forgot what was done early on.

The one trouble I have is the shop progress is focussed on big-tickets instead of actual milestones testings. They need billables, you need results. With a little focus you'll get fixed up

 

What milestone testings do you recommend? The current shop is scoping the coil wiring again.

The harness has had oil in it. That's why the camshaft solenoid was replaced. And I did see oil on the injector plugs when I swapped them.

 

...keyword AGAIN as in a circular loop.

I can't stand the way every ticket has been sold and you're left hanging near the starting point !

It is what is: shops need invoiced charges, no question it's a business.... somehow the focus on DELIVERING RESULTS gets lost.

If the target is to workout your misfires.... Once the ignition is trusted (plug/coil/boot) then I would focus on cylinder bore scope + compression pressure or even simpler relative compression.

That affects the ECU as in reset fuel maps.

If the misfire is affected by fuel, its not ignition, its the stock lean misfire. Test: Clear "ECU faults" to reset mixture watch effect on the fault count.
🤞

 

Mixture adaptations have been reset multiple times throughout each service that, on paper, would’ve affected them.

It definitely is frustrating to be left in the dark but at the same time, it’s not like I’m the shop manager. They’re not only working on my car and it’s also a complex, novel issue. But damn am I getting impatient right now about. The summer roads are calling to me and I’m left driving my other car, a boring Lexus SUV

 

And results have been delivered.

A camshaft solenoid was replaced that was leaking oil into the harness. Voltage issues were fixed with through replacing a bad alt. O2 readings were normalized from replacing O2 sensors.

and a multitude of possible reasons for the misfires have been ruled out in the process.

but they still remain of course.

 

So after another month at the last shop, no real progress was made aside from ruling out some potential harness issues and ECU. I took the car back last weekend and have been researching things a bit on my own and have potentially some actionable findings. I think I'm getting very close.

What really kickstarted my own journey was that I got a new code for "The position of the exhaust camshaft (cylinder bank 2) is implausible relative to the position of the crankshaft". This was highly suspicious as the bank 2 exhaust camshaft was previously observed with having odd position data specifically during the cylinder 7 misfires. So that got me digging a bit deeper and I came across some investigations into timing chain tensioner and guide wear.

I got a borescope and checked out the bank 2 guides and chain through the oil filler cap.











It all looks very clean to my untrained eye although the guides are a dark orange. I think these are off-white new? So many a little suspect? Anyways, after this I decided to do a test by disconnecting the bank 2 exhaust camshaft position sensor and going for a drive.

IT WAS THE SMOOTHEST THE ENGINE HAS EVER FELT. I logged cylinder faults for the entire drive (40 min city driving). Only a few isolated single faults across 5,6,7. But I later realized the last shop left 6 and 7 coil packs very loose so that was probably contributing a bit...


So I got those tightened up and was considering next steps... I remembered my scan tool has a manual camshaft actuation test so I decided to try that out (with the CPS reconnected of course). Those results were very interesting. Video: https://imgur.com/nVaRJL0

When manually activating the bank 2 exhaust camshaft actuation, I get a huge spike to 27 degrees from the normal -15 degrees. In spec range according the scanner is -18 to -10. So something is causing the angle adjustment to be way off. After a brief discussion with my mechanic, he thinks it may be the phaser oil control rings. I wasn't able to find much about these from my own research.

I think at this point the typical adjuster failure points are ruled out as I've already done the 63 kit. The position sensor for the exhaust is brand new. The solenoid itself was removed, inspected, given a clean bill of health, and reinstalled. I think the testing shows the solenoid works.

Thoughts? I think the phaser oil control / seal rings might be the smoking gun!

 

The live fault you're getting is a correlation code.

That means check that camshaft:
-- for a shifted reluctor wheel through CPS hole opening.
-- (for unlocked VVT gear - Already new?)

 

The reluctor / pulse wheel ring seals is what my mechanic was mentioning as a possible failure point here. Mehenker even makes a OEM+ part to replace these https://mehenker.com/en/camshaft-rin...-m156-amg.html. Sold by 63 motorsports also https://www.63motorsports.com/afterm...156pulseorings

From what I understand, the OEM rings can break or get misaligned causing oil pressure issues for the camshaft adjustment.

This doesn't seem like issue with timing itself as the angle would be consistently off.

 

You're right... go ahead and compare all 4x live data for correction factors to see which camshaft stands out as marginal.

This will give you the live ECU perspective on your running engine.

The cam timing must be precise in fractions of degree. A lot of resources are deployed to make that happen. It's well tracked.
This may lead to uncover the solution...
🤞

 

Did we ever do a crankshaft position sensor in the early days of this? I'm so sorry I guessed it was a valve body issue in the beginning, this is a whole box of rocks. Usually if the engines trying to make fruitcake adjustments THAT bad the CKP is on its way out or something is going on between either the camshaft or crankshaft sensors to the DME

 

The CPS for bank 2 exhaust has already been replaced as it was leaking oil into the harness. Classic.

I did more tests today disconnecting the camshaft solenoid for bank 2 exhaust. (With the sensor reconnected). Same thing. Misfires and hesitation completely gone. Also did another test drive with everything reconnected after everything was up to temp and the difference was immediately noticeable. Hesitation and misfires near constant at cruising speed.

Afterwards I ran the same manual camshaft actuation on bank 1 to compare the readings. That side had the same spike to 27 degrees at the bank 2 exhaust.

At this point it seems certain there is something wrong in the VVT system. My current suspicion is the reluctor wheel oil seal rings as that’s the only key piece left untouched. I’ve ruled out guide or chain wear from my Borescope.

Even if the oil rings aren’t the culprit, I’ll have already done the work to get full access to the timing components and top end to really see what’s going.

As long as my shipping times hold up, planning to get this done over the weekend.

I’m looking forward to it. Triple checked all my parts, doing a few other things “while I’m there”. Going to document it all!

 

Nice work man, I'm tuned in to see this resolved

 

This separate reluctor shaft is really what feeds available oil into VVT phaser gear.

You're focused on these oil seals gone bad from exhaust heat is a great guess. New seals will minimize pressure losses.

> SCREEN:
I wonder if there's any sort of screen mesh filtering involved such as found in the M278 VVT oil valve.

It may be that exhaust valves are force driving the camshaft on low pressure from leaky seals.

> QUICK TEST:
-- You can get CPS data from ECU
-- Compare your Exh.Cam-1 live position vs. Exh.Cam-2:
-- Is it all over the place uncontrolled or trailing?
(intake/exhaust are totall different)

ECU complains about it, it's not gonna be seemless.

> STOCK:
We know when squirters begin to open, pressure drops and camshafts are jerked out of position on low pressure - Look right around 1250.Rpm

 

So I actually had some of this data way early on on my troubleshooting.
https://mbworld.org/forums/w212-amg/...ml#post9161084

The key part of that post is the video logging all camshaft angles during the cylinder 7 misfire events. You can see bank 2 exhaust is all over the place. https://imgur.com/a/qnb06hR

The right side (bank 1) was in the range of -5 to 0 throughout the 17 second clip, while I saw the left (bank 2) range from -11.67 to 20.44.

There is an oil screen attached to the camshaft adjuster solenoid. The bank 2 exhaust solenoid was removed and fully inspected by a previous shop where it was given a clean bill of health. Part of this was cleaning out the oil screen, which was already clean.

The way I see it, the phaser wheel oil seal rings are the only weak link left in the VVT system. Regardless, I’m going to fully inspect everything else part of the VVT system while I’m in there. Getting a better look at chain slack, guide wear, chain wear, adjuster phaser wear, phaser wheel teeth, phaser wheel oil rings, any weird debris, etc.

Everything points to something being off with the VVT system itself and I plan to uncover whatever it is.

 

Yes! You did have this cam timing issue captured screaming at us, yet unnoticed.


not far apart


far 22° apart + voltage yoyo draining AGM


crazy 32° apart !!!


nearly equal

Now the misfires have a cause identified...
what's messing up cam timing is still unclear.

Many good reasons to have bad hydraulic position, including seals.
Is the Exh. VVT lock simply loose??

 

Right… many reasons indeed but most, if not all of which, should be visibly apparent once I have the timing and valve covers removed.

I think it’s unlikely to be an issue with the timing itself given timing is correct any other time. And the adjusters themselves have already been rebuilt. Hence my suspicion lying with seal rings or maybe the chain guides or tensioner.

It seems clear the problem is isolated within the VVT system considering it’s completely gone once I remove the control inputs via the CPS and solenoid.