tadiguy

The title of this thread is very fitting for me. I too have a 2014 GL550 with engine knocking noise. In fact, it sounds just like the videos/audios and @Floridah opening description is exactly as mine. I've done more characterization of the problem and eliminated several potential culprits. I will continue sharing my troubleshooting and findings on this forum to solicit inputs and share knowledge and hopefully eventual resolution or at least a root cause of my knocking issue. I'm wondering whether I should continue using this thread for that or start a new one. What's the best practice?

ybros-united

I have the same problem, same vehicle and the miles also 75k… really head ache.. did you get any solution bro?

tadiguy

Did your problem just started? Can you share some history of your vehicle and the occurrence of the noise? What makes it better or worse? How does it drive other than the noise? We're all trying to compare notes to find the cause and hopefully the solution

silvergl

If it were me, I would get the cylinders scoped and see if you have scoring. I had the same issue for a year, no codes, or anything, other than a knocking.

tadiguy

The problem is no one has drawn any correlation between cylinder scoring and the knocking noise. Yes, the M278/157 are susceptible to cylinder scoring but is that what actually causes the knocking noise and if so, how? What is knocking, rod knock, piston slapping, etc? See my analysis above and at this thread. https://mbworld.org/forums/ml63-amg-...ml#post8751235. I can't find a theory to explain how the knocking noise is related tot eh cylinder scoring.

Over the past few days, I felt my knocking noise got quite louder than I'm used to and yesterday my "check oil level at next refueling" message came on. I'm losing oil largely from external leaks and perhaps from my scored walls which are issues I plan to address. After I added oil all the way up to the full mark level, the knocking noise at idle subsided greatly almost to the point of sounding normal. If I didn't know to listen for a knock, I'd have missed it. It still knocks slightly under acceleration and idle and practically disappears when I shift to Driver or Reverse. This together with everything else I've observed/done makes me think it's caused by a hydraulic component in the head rather than cylinder scoring, piston slap, rod knock.

I think the cause of the knocking has largely eluded the community because as soon most people stumble upon the scored cylinder as part of the knocking investigation, they give up and replace the engine or sell the vehicle. The scoring is a problem (that must be addressed in due course) but is that what is really causing the knocking?

arsupisemnet

There are number of knocks in that particular engine, could be knock due to hydraulic valve lifters - that is what you actually had, since once you put oil at proper level it disappeared. Piston knock only appears then the gap between piston skirt and cylinder walls is too big, i could actually tell you that piston noise on LS engine appears at about 0.004 inch clearance. The reason i know it is because i did machine work and whoever put engine together complained about knocking sound trying to blame it on me, and in the end it turns out that cheap sas pistons they put in were 0.002 inch smaller in diameter for 4 pistons in set, giving 0.004 total clearance where piston slap start to appear.
Another knock could be due to camshaft wear, there lifter rollers goes in and out of wear grove, it is very common for these camshafts.

tadiguy

Thanks for your insights. So a mere 0.004in clearance can cause knocking? That's why I'll leave any machining/assembly operation for my future rebuild to folks like you who have the experience to meet all the tolerances.
I thought it was hydraulic lifters too after I correlated the noise to firing events on cylinder #2 (see post 24 for my noise analysis). After some analysis of the problem I replaced all 16 rocker arms and valve lifters on bank 1 with new after what I thought was excessive lash clearance on some valves (I think the lash clearance may have been due to the camshaft not fully seated since the valve cover and bolts provide hold-down force for the camshafts). Anyway, so the following didn't make a difference:

• Replacing all 16 rocker arms and valve lifters on bank 1
• Replacing intake camshaft actuator with new on bank 1
• Replacing intake camshaft with a used one I had lying around from a previous repair to fix spun tone ring on another M278 engine. That car didn't have knocking noise so I assumed the cam lobes weren't badly worn out
• Replaced exhaust camshaft and actuator with a known good used one

I also inspected the rabbit holes and cam lobes for wear and didn't find anything obvious. I inspected the oil galleries for the lifters for blockage to the best that I can and didn't think they were blocked. I even thought about removing the rockers and lifters from cylinder #2 to see if the noise would go away but quickly realized that would prevent oil from reaching the lifters on cylinders 3 and 4. If you have any thoughts about how I can conduct this experiment let me know.

Any thoughts on what else could cause the knocking noise that is improved by increased oil volume? It's not completely gone (only reduced) even with oil at the proper level. See my other analysis of oil pressure and cylinder compression along with other observations in this post https://mbworld.org/forums/ml63-amg-...ml#post8751235

AutomationJunki

So, I’ve been chasing a similar sound. I only hear it when under load, not when revving the engine in park or neutral. I’ve been driving with this annoying tapping/knocking for about 15k miles.
It’s annoying the crap out of me and I can’t figure it out. Likely need to bring it into the shop. One thing I did notice is that the high pressure fuel pump puts out a lot of vibration. I have a little bit of a hard start and rough idle occasionally. What I’ve learned is that these are cam driven fuel pumps and the rollers on the tappets go bad.

Has anyone explored the high pressure fuel pumps as a source for this kind of noise?

tadiguy

I've taken my high pressure fuel pumps apart quite a few times during the numerous occasions I've removed the valve cover to investigate this problem. I didn't find anything odd about the pump pistons, rollers or the cam lobes that drive them. Also, the noise seems more towards the front of engine; fuel pumps are situated in the back. I actually listened to the pumps with a stethoscope and the noise isn't coming from them or that area. Keep us posted on what you find at the shop. Hopefully they won't quickly conclude that you need a new engine. Of course a new engine will make the problem go away, but what is really the problem? Same here - driven a few thousand miles with no performance issues and noise isn't getting any worse except when oil is low.

Galen Foster

9300 miles is your oil change interval?

AutomationJunki

I will absolutely not replace this engine..basically I’ll wait until it goes and then get a used engine or part this thing out.

I’m curious if anyone has actually had this issue AND had a catastrophic engine failure.

I’m knocking on my wood steering wheel😃

AutomationJunki

I have 156k miles with this same noise. Have been driving it for 15k+ miles like this. I have had 2 issues while driving where at highway speed and accelerating to pass I’ll get severe hesitation and a check engine light. CEL code is for a low fuel pressure in the rail on the side where the noise is coming from. I also suffer from the occasional rough idle too. The other odd symptom I have is on some days I average 16mpg and others 19…same drive, approx same speed.
I have an appt for 8/30/23 to have this diagnosed before I start throwing parts at it…

chassis

If you decide to start throwing parts at it, I would replace or check:

- main battery
- aux battery
- ignition coils
- spark plugs

- measure compression
- borescope
- diagnose fuel and ignition performance ideally with XENTRY

gladerider

i have the same noise. i have about 140k on the clock. had it for about past 15k or 20k. been putting liquimolly products during oil changes. that did improve the sound a little bit but not as much as i'd like. i just did another oil change a few weeks ago but this time without the liquimolly products. the noise is much louder. one liquimolly product is the lifter cleaner.

tadiguy, did you see oil passages in the lifters? supposedly there is a oil passage for the lifters? that can get gunked up? not sure what that means but i've seen a few videos of people claiming that they have improved their lifter noises in their M156/9s

tadiguy

The oil passages were clear although I shot some brake cleaner and compressed air through them to make sure they’re clear. I also followed up with engine oil flush and lifter additive. It’s made no difference

What was the code? Fuel injectors are known to go on this engine, but could also be the HPFP. It may not be related to the noise. Please keep us posted on your findings.

ZeeGermanz

Regarding the knocking noise, be sure to check injectors, plugs, and coils. If one cylinder isn't detonating, the engine is going to knock. Bad gas, weak injectors, fouled plugs, dead coils, can all cause knocking. Coils and injectors commonly fail, it's not always going to trigger a sensor and trigger a cel.

So before anyone assumes they've got a worn camshaft or bad piston, take it to the dealer and have it diagnosed. These are very reliable engines, despite what chicken little says on the forums.

silvergl

I had the dealer diagnose the engine twice. First time in the car, they would not tell me what was wrong with it, only that I needed a new engine.
The second time was after I had another shop replace it and I had it for sale. They came to inspect it to buy it for a customer, scoped it, told me cylinder 5 was scored and they would not buy it. Subsequently I sold the engine to a board member who in the rebuilding process documented that actually cylinder 5 was one of the few that was fine. It turns out the defect was likely in the manufacturing and if I were smarter, or had a better dealer, they would have discovered this and the engine should have been replaced under warranty.

So, its not always chicken little. In my experience the hurdle will be finding an honest dealer.

tadiguy

Thanks for your input. Even without CEL, there are various ways to determine bad coils, injectors, plugs including physical inspection/replacement/swapping, signal analysis, live parameter monitoring, active test, etc. Injectors, plug, coils are quite basic and the quest for the root cause (at least for me) of this noise is beyond that point.

There are no assumptions of worn camshaft, pistons, etc., being made here. It's a systematic check and elimination of the most likely culprits given the symptoms. I'm not sure how much of the details in this thread you've read. We provide as much background as possible and expect contributors to take that context into account. Dealership is often not the answer (after all that's the essence of this collaborative self-help forum). Dealerships often don't have time to troubleshoot such elusive problems and most customers aren't willing to pay more than an hour or so of diagnostics anyway. When faced with a problem like this, most dealerships will go for the low hanging fruits (replace coils, plugs, etc. at customer expense and not offer refund even if it doesn't fix the problem) or require an engine tear down (and are always quick to add "and go from there") and in the end will be an expensive engine replacement (since they don't rebuild) on top of all the wasted time and money on diagnostics and unnecessary parts.

arsupisemnet

Zee Experd or Exturd most likely expressed his valuable opinion on the matter he knows less... Meanwhile other guy in the forum has dead "reliable" engine at 50k miles, but judging by the cover, he has aftermarket boost program (so goes engine life).... Qua qua...

tadiguy

Hmm. May be I took Zee Experd too seriously on this one, but I guess you're right because then I'm not sure what kind of engine is in his/her Germanz car. In the cars I driver (or work on), it sure is a great thing when "one cylinder isn't detonating." No knocking - just the quite rumble of an internal combustion engine like they're meant to run, Germanz or not. Haha haha haha ...

ZeeGermanz

Ok Thanks

ZeeGermanz

Not one mention of the most likley causes of engine knock on this thread until yesterday. Just a long thread about how it's obviously total engine failure. Who needs diagnosis?

arsupisemnet

1) Junk? How come "reliable" engine suddenly become junk?
2) There is a trend between block wear and knocking noise. I don't need to explain anything
3) You been around here for about couple months, making 4 posts, siht, and suddenly become "Google" expert, while others been doing tremendous work explaining how things work and how it is possible to repair it....
In general i am a last person you would want to get into fight... Here or for real... I don't rebuild junk, i rebuild un rebuildable and exotic... And in the most cases i don't charge enough even just to make a profit... Booooooyyyyyy
In general regarding your expert comment - misfired cylinder will not make knock noise unless there is an extreme wear....

tadiguy

Dude! chill!!
If you meant to make a meaningful contribution, you don't start calling names in just your second post on this forum. An no, you didn't suddenly shine a light in our minds about the most likely causes of this engine knock. In case you don't realize it, the ignorance (and arrogance) you express on this matter is stark naked. You probably read some botnet generated info on the Internet and decided to chime in as an expert because you don't sound like you have experience or expertise in diagnosing any of the things you mention. Let me help you analyze your post:

• You state "If one cylinder isn't detonating, the engine is going to knock." You can't be more wrong than that. You obviously don't know what detonation is; you saw it somewhere, didn't know what it means, it sounds cool and technical and so you thought you'd use the term to sound like you know what you're talking about.

• You state "Bad gas, weak injectors, fouled plugs, dead coils, can all cause knocking." Again, you heard the term knocking and you're obviously confusing combustion related knock with what we're talking about here. And you are wrong again: bad gas, weak injectors, fouled plugs, dead coils don't typically cause knocking; They cause misfire and that is neither called knocking nor sound like one.

Have you actually heard a knocking sound or diagnosed and engine before? Did you even listen to engine noise in the video and audio by other members in this thread? Most of us do know how to diagnose ignition/combustion problems and don't need the idiot light or ignorant/arrogant commentary.
You seem to know just enough to be dangerous like we say in my professional arena. It's best to stay off this topic and thread.

AutomationJunki

Took my 2013 gl550 157k miles into a import shop….Paid $260 for them to tell me it needs a new engine. I asked how did they know..told me they listened to it. I asked did they check cylinder pressures, scope it, etc. Nope. They believe its a rod bearing and it could go out at any time. Today I’ve put 100 miles on it and revved it to 5k rpm just for the heck of it. Still running.