JPnorthSouth

Hello everyone! I have a 2014 Mercedes-Benz GL450 4Matic V-8 x166 with 175,000 miles. Just had dealership fix a valve cover oil leak and complete tune-up, but now I have an engine light, knocking and power loss from cylinder 2. Dealer scoped and there is some scoring. All dealer could offer was $37k engine replacement. I'm currently in Fayetteville, NC and moving to the Macon, GA area for the next 3 months. I've considered swapping in a used engine. Any suggestions on how best to fix the problem or a reputable mechanic to bring it to?

Ricardoa1

What were the codes you got. Are you getting misfire codes? At that mileage you might try sending it to auction if you have one available. Fixing will likely exceed the value of the car. And that’s just not smart. You will probably run into the same issue with a used engine. The pool is too risky. Unless you find a shop that will do it cheaply and you find a used one in good shape that is not overly expensive, you can try rebuild but that would require a core of some sort and a down car for months at a time. You might need to sell as a parts car and cut your losses.

Scores can happen as early as 80k. Most original engines past 100k probably have scoring but functional to where no issues are present. What are your symptoms and codes be more specific to properly assess.

Whatever you decide good luck with the outcome.

JPnorthSouth

The dealership did the diagnostic and reported that it was a misfire code. They supposedly tried swapping spark plugs and still received the code on the same cylinder. I bought the vehicle from an auction and there was some scoring then, but the oil was clean and we had no problems except a small oil leak. We learned of this engine defect and recall when we first had it serviced after purchase. I use it to pull my travel trailer and noticed the oil leak from the top when pulling uphill. So, we fixed it. The valve cover was off when we picked up the vehicle from the dealership the first time, so I'm a little suspect about the quality of work and upon return with this issue another customer was giving them the business about their vehicle running terribly after repair. A $3-4k fix outweighs a purchase for me, especially since we have no other issues and have added over 30k miles in 9 months.

chassis

A replacement engine, assuming it’s preowned, will have equal probability of scoring as your existing engine. Therefore it is a risk-reward and cost-benefit scenario for you to evaluate.

The M278/M157 has a host of other issues at 80k+ miles which are not inexpensive (e.g. turbo cooler lines, oil in harness, valve guides, intake valve deposits).

I wouldn’t participate in the replacement engine scenario above and would sell the vehicle and move on to something else.

Ricardoa1

Misfires could be from a bad fuel injector or ignition coil or bad spark plug. But to check the cylinder mechanical integrity you must do a leak down test and or a compression test. If this passes then try any of the three items mentioned. Spark plug, ignition coil/boot and spring, and a fuel injector. But if you have valve issues or causing excessive oil ingress and fouling the plug that’s another issue worth looking at as plugs will only last so long before they foul again.

Finding and paying for proper diagnosis to eventually get bad news means very few will do the lengths and just go with worse case scenario and start over with a new engine or new car.

scoring and good compression means you can keep driving. Assuming all else is in good order.

mcoady1

This sounds like a bad valve. Depending on the repair price of the valve job on that bank, I'd just repair it and keep driving it even if there is scoring. arsupisement had scoring and only learned about it from a loss of compression, which was from a bent valve.

tadiguy

Check if compression and leak down tests are good then misfire is not due to mechanical damage. In that case don't discount a bad fuel injector that others mentioned. I fixed one for someone recently that needed two bad injectors. The irony is that he bought it at auction through a dealership and an insider from the dealership told him not to buy it because the engine is no good. Yes, it had scoring in the cylinders but it didn't affect compression or leak down test. After diagnosing and replacing the two bad injectors it run fine with no other issues. Bench testing the injectors per WIS resistance spec passed but they still turned out to be defective injectors.

BTW: it's odd that after the dealership swapped the spark plugs and the problem stayed with the cylinder #2, they didn't proceed to do compression and leak down test to check integrity of the cylinder and valves on cylinder #2. Let them know they didn't deliver on their diagnostic charge and find another dealership or indy to do proper diagnostics.

Ricardoa1

I agree with tadiguy. I said the same in the other thread with engine issues. If the valves are sealing during the leak down test. And there is enough ring seal during the compression test then move to, plug condition, ignition coils and testing replacing injectors.

Cam and follower damage can be inspected with valve covers off.

Timing chain and tensioner noise should be easy to investigate with a scope.

rod knock increases with rpm

piston slap is possible but doesn’t seem common on these engines usually iron sleeves aluminum pistons do this more frequently. Most ignore when their engines are prone to it as it only lasts till engine warms up and piston expands enough make it quiet.

tadiguy

@Ricardoa1 Do you have experience with rod know on the M278 engine? I have nasty knocking on my '14 GL550 that I've described in these threads below. I'm still looking for insights into what to check next short of pulling the engine.
https://mbworld.org/forums/gl-class-...ml#post8693205
https://mbworld.org/forums/s-class-w...ml#post8690244

Ricardoa1

not with the M278, but same principle applies any engine.
Bad bearings and rod knock will be picked up on an oil analysis. You might even be able to see it in the oil or oil filter if bad enough. A rebuild or replacement is needed if so noise will just get louder with time and the metal in the oil will do damage to other bearings and parts.