SSB3435

Update after having covered 850miles... No change on shaking so far... As miles pass by with driving, more and more I start thinking about that my left cylinder head/valves or valve seatson cyl#8 are permanently bad and leaky. Seems like they cannot hold the combustion chamber pressures over a certain limit..

SSB3435

I just found time to check my engine number last weekend, yes it is way over 128000... 360541 is my number and according to the service bulletin, my left cylinder bank may be problematic which is exactly the case on my car. If the de-carbonization will end-up unsuccessfully, I try to have it changed by the dealer and negotiate with a possible/partial warranty coverage. since it is a well known problem.

FWP!

Well, that is sad to hear. I wish you luck at the dealer and let us know what happens.

pjw1967

CPO 2017 GLS550 45,000 miles. I complained to the dealer that the car ran rough at idle. There also seemed to be soot on the back window whenever I wiped it off. They changed the spark plugs and redid the motor mounts. But reading this thread has me worried. I looked at the service doc. It's dated Aug 6, 2015 (or June 8, 2015). My engine nbr is 27892830334160. My car was built 12/5/2016, a year and a half after this bulletin was released, but the EUI seems to be well past the number in the bulletin. Am I reading this right?

chassis

Your engine is in the affected range for the bulletin. Black soot is not normal. Hand the dealer the bulletin and tell them to follow the instructions.

John CC

Does that work?

pjw1967

We're gonna find out......

SSB3435

Unfortunately dealer rejected my request because my GLS has a total loss record in 2021 (flooded in NJ and I bought it from the auction, replaced some of the interior ECU's and seat sponges/harnesses, everything is OK except this engine issue. I believe engine problem is not relevant with the flood since the car was flooded when it was stationary and the water level was around side steps/doors junction so no possibility to damage the engine head). I talked with my contact at the dealership, he said their systems are somehow integrated with DOT/DMV or whatever it is, all the totaled cars are automatically goes out of warranty/goodwill. So no luck for me, still driving it with the same issue, no better habit observed so far. At the worst case scenario, I may take out the LH cylinder head and have it reworked for get rid of leaky valves on cyl#8 and put it back with new gasket and head bolts, trying to keep the cost of repair at the lowest.

SSB3435

UPDATE: I ran out of all fuel/oil additives, no change in engine behavior. So I decided to remove the left bank cylinder head to work on the cyl 8 valves and valve guides. The compression on all 7 cylinders are good around 210-220psi on cold crank, but cyl 8 dropped down to 185psi (was 215 before I drove it for 1,500 miles approx). Looks like either the intake valves have been elongated or valve seats/guides are prematurely worn (as described on the service bulletin I shared) that result in the leakage back to the intake port under extreme pressures (low rpm/high load conditions). I cannot explain the perfectly clean looking cyl 8 intake port where the remaining 7 intake ports show some dirt and carbon deposit. The leakage from intake valves should be washing all the dirt in cyl 8 intake port, otherwise it can't happen.

PeterUbers

This is all over my head and I read the entirety of this thread and I have to commend the OP in his skills and this forum for supporting him with great info. Cheers

arsupisemnet

One of the high pressure fuel pumps. Misfire due to lack of gasoline supply

SSB3435

I have tracked the injector rail pressure with STAR diagnose, it seem stable when jerking occurs. Also I do not get 'HP fuel line pressure below threshold' DTC, I assume this DTC should be triggered if the pressure would deviate from targeted pressure. Despite the symptoms look like HPFP or more widely a fuel supply/injector etc problem, I cannot answer these two questions:
1. Why cyl#8 intake port is perfectly clean while the others are mostly black with lot of carbon deposits?
2. Why some cold starts happen with 7 cylinders only where cyl #8 do not fire but comes back to life after 2-3 mins of driving?
These two observations make me think that, cyl #8 has a compression problem caused by leaky valves.
Still working on it, will share updates asap!
Thank you!

John CC

That sounds reasonable. Does it happen on every cold start? If so, can you perform a cylinder leakdown test on it?

chassis

XENTRY has the ability to turn on/off injectors to isolate malfunctions. Do you have XENTRY?

SSB3435

Yes I have XENTRY too. The thing is, problem is intermittent on cold starts but can be repeated everytime when driving. If engine starts good in the morning, the idle is perfect, no issues, no CEL. Take it to the highway, manually engage 5th speed or higher and floor it, BUM! Engine shakes and cyl #8 shuts down with P0308 DTC recorded. Ignition off and on, everything comes back to normal until you repeat the same thing: Low rpm/high load conditions.

Regarding the injectors: All 8 has been sent to local BOSCH service center, cleaned and tested. All 8 passed the test. To be on the safe side, I swapped injectors 5 and 8, recoded them in the ECU. Problem is still at cyl #8. Swapped them back to original locations and recoded. Same cyl #8 has the problem. This proves to me that, injectors are not the actual cause of the problem.

SSB3435

I did not perform the leak down test, my bad... I focused too much on the intake carbon deposit cleaning these days assuming the problem will be solved with deep cleaning (recommended by a MB tech at the dealer), I overlooked the leak down test stage.

The problem repeats 30-40% of the cold starts, otherwise start perfect, as intended. Very rarely, maybe 10% of the cold starts, car starts normal and during heating up stage -in 10-20 secs after the start- slowly starting to shake and misfire, then end up with cyl #8 shut down by ECU and CEL.

arsupisemnet

Injectors are not, your spark plug coil or ECU is the problems. Since you still have 12 bar - which is more than enough to perform - and your chamber is clean, because being literally washed by gasoline (no spark).

SSB3435

8x spark plugs have been replaced with factory ones, the same. Ignition coils swapped, the same. 8x ignition coils have been replaced with brand new ones, the same. These were the first thing that we did, as for all misfire problems observed.

I have also ordered another engine ECU, recoded the VIN with Flex, the same. With all that effort, the same problem is there. I think, I have a cold crank compression around 185psi BUT the intake valves are leaky under extreme pressures (you know the combustion chamber can reach 2,000 psi after ignition on turbo engines).

arsupisemnet

I wouldn't conclude as a valve issue in this. I had one cylinder with burned valves (low pressure) and I drove all the way to ECU governor without misfires or jerking... Only thing was small shaking on the idle.

arsupisemnet

It is a high pressure pump malfunction, since all your miss fires goes on the same side of the engine - means same fuel ramp. Other thing could be camshaft phasers, to have engine to jerk around it is not one cylinder issue.

SSB3435

Last report about the car: Finally we have performed the leak down test on cyl 8, it shows approx 30% loss which is not good. On the other hand, I asked to a MB expert friend of mine to check the cylinder walls and piston condition with his endoscopy tools (which are much nicer and professional than mine). The result is not encouraging.. With his 15+ years of MB dealership experience, he told me the car has 99% stuck piston rings issue on cyl #8. Despite there is no scoring observed on the cylinder walls yet, the Silitec coating looks almost gone. Probably due to misfiring and non-ignited fuel continues to tear down the oil film and damaging Silitec layer. My tech said, rebuilding the engine will cost a fortune so may be better to find a salvage engine and swap it (of course there is no guarantee for the junk engine to work perfect, there is always a risk) or sell it as is. Probably I will go with the 2nd option and swallow the investment already done to rebuild the car. This is what it is...
Thank you all for the contributions so far. I am closing this chapter and start looking for a replacement GLS, probably the new body X167 with V6 engine. I had enough with M278

John CC

When you performed the leakdown test, did you positively identify the source of the leakage?

SSB3435

No, no further analysis done, when my tech guy told me he saw the very shiny cylinder walls which means the Silitec coating is almost gone (but there is no scoring yet) I lost my motivation to repair that engine. I mean, if the repair would require the engine teardown, I won't do that. Too much additional $$ and time investment required.

SSB3435

Here I attached the video of a bad cold start, where cyl #8 does not fire and engine ECU immediately shuts off the injector. Besides all of the possible mechanical issues, this is really weird to me. I have the 185psi cold crank compression, brand new injectors/spark plugs/ignition coils installed, wiring harness is good (even I wired external lines to try, nothing changed) so what is missing for cyl #8 to work at cold start? Maybe the timing information from crankshaft sensor is bad at certain rpm range?

Years ago I was working on a Maserati Quattroporte on which CEL comes on intermittently with misfire on cyl 5 DTC P0305. We did everything possible but problem was still there. Later I investigated the service history of the car and I saw the starter motor has been replaced 2 times. With further investigation we saw the bad starter motors damaged the toothed wheel on crankshaft (starter gear lightly grinded some teeth already) and we concluded that would cause of the misfire, making the crankshaft position reading bad at certain rpm’s. Do you think that may be my problem too? I have replaced the complete transmission (flooded one was having a bad hydraulic block) and this job was done by a butcher mechanic. I am afraid he already damaged the toothed wheel while turning the engine with metal stick from the toothed wheel, to be able to fit the torque convertor bolts. Does that make sense?

An example of what I am talking about:

John CC

I only mentioned that because when preforming a leakdown test it is no more work to identify the source of the leakage, and that would give you one more data point to confirm the diagnosis.