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Thanks for sharing your findings; it's similar to what I experienced with disabling injectors. I had higher engine smoothness values for cylinder #2 which also seems to be source of other anomalies I've detailed above.
Interesting reading everyone’s comments as I too am experiencing the same noise. 203k miles now, 20% of the time towing an enclosed 16’ / ~5m trailer with 4 dirt bikes + gear.
Personally wrenching on this vehicle for last 5 years performing all work. Noise definitely quieter after fresh oil change. When cold, noise less apparent. When hot (towing trailer to Death Valley from San Jose) noise definitely there. Drove it from CA to FL 2x with 4 grown adults and absolutely packed out with stuff. No loss in pickup, throttle response, fuel mileage - noise remains.
Will keep driving it until something else comes to pass.
For the moment, not better nor worse. Having experience building motors & tearing them down with rebuild across gas & diesel, the sound pitch points to the motor top end (really appreciated the filter applied to audio file- very industrious) & not the bottom end (rod, pistons, crank).
I use only Mobil 5/30 every 4500 miles for oil change.
if something else arises, will update thread.
Preparing to replace all suspension struts, bushings, ball joints after tromping through high & low desert of Death Valley last 5 years. She’s performed well considering the terrain traversed.
Agree with other member comments:
1. absolute crap coolant connectors that are intentionally designed to fail around 150k after spectral analysis of remaining debris pile. One in particular stands out - location is right of centerline when facing engine at the firewall - follow the hose and you’ll see it. Photos below.
2. what vehicle can be purchased for 8k - 10k nowadays?
3. Anybody else have the factory installed tow hitch that doesn’t recognize a brake controller when connected to the factory green connector under driver’s side rug directly under the brake pedal at the firewall?
As I too learned, buy MB parts through mercedesbenzstarparts.com, perform labor yourself if a stretch possible - dealers mostly not interested in solving the actual problem rather throw parts at it & let owners absorb the cost for their indifference.
Crappy firewall hose location to be proactively replaced. Old vs new hose pipe. Heat affects all these hose pipes around 140k-150k miles due to material selection.
The knocking noise saga. comes to the end. Two major factors contributing to it
1) Wear of tensioner (internally) - usually stuck due to wear and easy as temperature goes up
2) Wear of camshaft lobes - both or exhaust camshaft on driver side goes bad causing knocking noise as it goes due to grooves on lobes - basically rocker arms jumping in and out of grooves unable to compensate for lash.
Service adviser will advise to change timing chain and adjusters were real reasons mentioned above.
Can you list the respective part numbers for the items you feel responsible for the noise? Would greatly appreciate it!
Is anyone did dynamic compression test before digging holes in the ground?
Actually yes. Both cranking and running dynamic didn't reveal any obvious anomalies across all cylinders on bank 1.
For folks that aren't familiar with this sort of analysis, the two peaks cover TDC to the next TDC for cylinder #2. The alternating blue bands correspond to the four cycles of a 4-stroke internal combustion cylinder: expansion (or power stroke), exhaust, intake and compression. Problems with intake and exhaust valves among other in-cylinder problem will show differently but I won't bore you with the details of the analysis. The bottom line is this cylinder, which I believe to be source of my noise, looks healthy. I know from other tests that it's slightly low on compression but that won't explain the noise.
This running dynamic. It may look odd, but every other cylinder looked the same including another good car I used as a reference. The variable cam timing is probably why there are no well defined characteristics.
I shared this on another thread back then and will add here for completeness. There is no sign of oil pressure being a problem either. The characteristic and values below agree with MB spec for the map-controlled variable oil pump with two pressure settings on this engine.
Can you elaborate on how this contributes to the subject of engine noise issue in this thread?
Whenever an issue comes up, we can look forward, i.e. find a fix, or look backward, i.e. understand the root cause/contributing factors.
For the OP, the fix is definitely of upmost importance. For those watching from the fence: understand the root cause and addressed early before it arrives.
Whenever an issue comes up, we can look forward, i.e. find a fix, or look backward, i.e. understand the root cause/contributing factors.
For the OP, the fix is definitely of upmost importance. For those watching from the fence: understand the root cause and addressed early before it arrives.
Root cause analysis comes after the nominal cause is found. We're collaborating on this thread to hunt for the nominal cause before we can even think about root cause. I'm not trying to dismiss your contribution but I must note that it will be far more useful if you can synthesize and contribute the relevant info you have instead of throwing in a couple of links and a terse comment. For instance, if you have information that "the 2-stage oil pressure causes 123 which leads to ABC and hence the specific engine noise described here" that will be good. Similarly, if there is some pertinent info in the video link it will be nice to say it so that anyone watching can lookout and understand the information better.
Root cause analysis comes after the nominal cause is found. We're collaborating on this thread to hunt for the nominal cause before we can even think about root cause. I'm not trying to dismiss your contribution but I must note that it will be far more useful if you can synthesize and contribute the relevant info you have instead of throwing in a couple of links and a terse comment. For instance, if you have information that "the 2-stage oil pressure causes 123 which leads to ABC and hence the specific engine noise described here" that will be good. Similarly, if there is some pertinent info in the video link it will be nice to say it so that anyone watching can lookout and understand the information better.
I hope you understand that forum members participate here voluntarily (and sometimes from a phone) and I hope sincerely to help, not distract others. Since you want a summary of the data provided, it will come into pieces (since I have job responsibilities first and foremost)
Here is the opinion I have made, therefore biased, over the last few years about the M276/M278 from the great information available in the forums. I am sure most of the following is already known to many of you in this thread, but just my take on it.
1 - These engines are hot, and push a lot of HP/L ; therefore, they require LUBRICATION at its best. There is no substitute for lubrication except having the engine OFF
2 - Some of the issues these engines have shown include
- Rattling TSB --> Root cause was lubrication, and MB has patched the symptom with a check valve and replaced the chain tensioner (not clear to me if the tensioner was upgraded)
- Cylinder scoring/scuffing --> Root cause? extreme high temperature where expansion between sliding components without the best lubrication
- High-pressure fuel pump wear (right side) --> Root cause? lubrication between the lobe and the camshaft
- VVT cam gear wearing out --> Lubrication at the locking pin
The common theme is that due to lubrication (in my mind) is affecting the top-half of the engine. Oil starvation due to poor design, bad oil pump, or poor oil management? The link I posted refers to the ECU managing the oil pump and lowering oil pressure within idle and @2500+RPM. Also, the ECU shuts down he oil piston squirters under "certain conditions". Such low oil pressure will starve the farthest section of the engine: HPFP, Vacuum pump, and last 2 cylinders for the V8, The last two in the V6 may be lucky to be closer. Also, less cooling of the piston can only make things worse by running them hotter.
On the video, it is very illustrative of the moving parts that could create noise on the top of the engine, and what wear on these engines look like. I do not have hard data on what cylinders are more prone to scoring. Such data will be great to collect to see if it correlates to the distance to the oil pump. In the video, there is something that caught my attention: two head bolts (one on each head) near the back broke when removing them. Wonder why? Over torqued by the machine during assembly?
On the oil pump management, there has been a conscious decision, the ECU is acting as designed, to allow the engine to get hotter, and cook the oil a bit more (therefore, the best clean oil possible is needed).
In the case of the OP engine, improving lubrication would be just a band-aid if damage (either in the cylinder, HPFP or front timing components) has already started.
Leave it here for now.
Last edited by juanmor40; 12-04-2023 at 11:55 AM.
Reason: Attachment
And that is the right question. As a matter of fact low idle oil pressure is not related to the issues you listed above.
There is another tandem oil pump mounted on back of main oil pump which is against all the logic is (pay attention here!) pumping oil out of twin turbos. And where oil comes from? Right, from the top feeder on each cylinder head.
So if something is dying there because of oil starvation is due to turbo oil pump
And that is the right question. As a matter of fact low idle oil pressure is not related to the issues you listed above.
There is another tandem oil pump mounted on back of main oil pump which is against all the logic is (pay attention here!) pumping oil out of twin turbos. And where oil comes from? Right, from the top feeder on each cylinder head.
So if something is dying there because of oil starvation is due to turbo oil pump
Perhaps my written English is not clear. I did not say low idle oil pressure, but the ECU keeps the pressure at idle value up to 2000+ rpm.
This engine as new with perfect idle oil pressure, and the ECU still commands low ( idle value) pressure at will between idle and a set rpm value.
Rather people read the threads , if sparked any interest, and make their own conclusions. I would learn from the feedback , if any, as well.
Well, if you actually spent time reading MB intro on new engine design, you would know, that oil pump pumping on 1 bar pressure before 3.5k rpms. But that is not an issue connected to extensive premature wear of timing components. The issue as i clearly explained above - is a suction oil pump for turbos which cause oil starvation in cylinder heads.
The info about oil lubrication is all good to know. I'm quite aware of the oil pressure management in the M278 which is why I went as far as measuring the dynamic pressure on my engine (see post #81) to compare to to the specification. The merits of M278 oil management design, performance or lack thereof, etc. and how it contributes to wear and other issues can be debated in a different context. I started contributing to this thread because the OP describes an engine noise quite similar to what I have. Others have joined in describing the same noise and wondering what the cause is. To me, the goal still remains "what could be causing the noise?" so I'm expecting contributions to further that goal. For instance, if the lack of proper lubrication has caused wear on some component that is causing the noise, what could that be? If lack of proper oil pressure or volume is affecting performance of some component which in turn causes the noise, what could that be? I'll be happy to chase down all leads (and I have to a large extent) to find the cause of the noise. May be that expectation of keeping on topic is unrealistic.
On the issue of wear, I have physically inspected camshaft lobes, high pressure fuel pump, replaced lifters and rocker arms, cam shaft, cam actuators, tensioner, spark plugs, etc. along with other experiments. These have been methodical rather than casually throwing parts at the problem. My cylinder walls are scored but how could that explain the noise? I also mentioned in a previous post that I do see some correlation between low oil level and intensity of the noise so I'm not discounting oil delivery problems at all. The question is, if it's oil related, what is making the noise and why is there no evidence of wear on the major suspects like cam lobes, lifters, rocker arm, etc.?
My wild theory at the moment is the chain tensioner. It's not defective, but perhaps it isn't getting adequate oil to maintain constant tension. In a previous post, I described my observations about the tensioner seemingly pulsating in sync with the noise. The only reservation I have about this theory is why the noise (at least in my case and some others) disappears when coasting or in between gear shifts. Any ideas about what happens during coasting that can explain this? Any other thoughts about the noise? Please keep the goal in mind: what could be causing the noise?
Deal here is that as long as main pump in economy mode the tandem turbo pump pumping out at 100 percent capacity. You starving camshafts, etc. So if you can change tune for main pump to start pumping at full capacity lets say at about 1500 rpm you suppose to be ok, will be plenty oil everywhere.
11-30-2023, 09:03 PM
