austin814

I wanted to make a post about this in case anyone else has the problem. I couldn't find anything where someone had reported this problem, so I wanted to put the information out there for others. I have a 2012 E550 M278 with no tuning. 120K miles. I began to feel a very minor engine vibration at idle on Tuesday when parking the car, and then again on Wednesday when backing the car into the garage. On Wednesday the CE light came on as I was backing into the garage with codes for misfire on Cyl #8 and lean fuel mix on the bank. The M278 doesn't have a mass airflow sensor so I replaced the Mass Presser Sensor on the side reporting the problem and it didn't make any difference. The minor vibration turned into the ECU turning off cylinder 8 and 6, so I took it to a Bosch certified indy shop as I didn't have tools to check fuel pressure etc. I told them what I had done and the codes I had pulled. They diagnosed the problem as needing all new plugs, so replacing all spark plugs cost $550, but that didn't resolve the problem. Then they suggested replacing the injectors on #6 and #8, saying that compression was fine on all cylinders but those to injectors were failing. I approved that which made the bill $1,500, but that didn't solve the problem either. Now they want they want to replace the high pressure fuel pump and all 4 injectors on that side of the engine because they have said the HPFP is failing and is somehow leaking oil into the fuel and has damaged the injectors. The bill is at $3,500 now, and I hope this solves it. Just wanted to let everyone know my experience, in hopes someone else troubleshooting in the future! I'll post a followup when I know from the shop of this solved the problem!

atraudes

Sounds like they're throwing parts at it. They checked for vacuum leaks already, I'm hoping?

austin814

I'm not sure if they have checked for a vacuum leak but I do know it was throwing misfires (specific) and multiple misfire (random) codes. From what I understand a vacuum leak can cause the rough idle but does not throw codes? It seems odd to me that the High Pressure Fuel Pump is causing the problem, but it was ad idle that I felt the problem. You'd think the HPFS would cause a CE light at higher speeds, not idle?

davidjohnbamber

I would ask the shop doing the work if they are using M-B Star, or?

austin814

Update:
Talked with the shop on the phone about 20 minutes yesterday. They have done due diligence in troubleshooting this problem (involving Mercedes USA, reprogramming the ECU with a software update etc) and after new plugs, new injectors, new high pressure fuel pump and new engine control unit software the problem (misfire on 8, 6 and sometimes 5) would still came back after the vehicle was up to running temperature. They decided the next thing to check would be the exhaust. They got the vehicle up to temperature and then used a infrared temperature gun to check the exhaust manifold temperatures. On one side of the engine it was around 280 degrees (normal) and on the other side of the engine it was over 600 degrees. So this leads them to believe the catalytic converter is plugged, causing back-pressure and heat buildup on the side with the misfire.

I'll update on where things go from here

Mud

I'm not saying this to insult you, but where the shop is concerned, that's a ridiculous use of the parts cannon. Even a generic obd2 scanner typically can show mode 1-4 data, which includes real-time run data. Often when CEL may not be lit, that run data can show anomalies in sensor inputs, fuel trim, O2 sensors, etc. I'd be curious to see front and rear O2 sensor data for both banks. They should read very similar on both banks, meaning the front O2 voltage should be close on both B1 and 2. Same for the rear O2 sensors. The rear O2's are in place to verify catalyst efficiency. If there's a clogged cat I would expect to see a. very different voltage reading on that particular sensor.
Note also that a misfunctioning O2 sensor can cause poor running, so the sensor itself needs to be verified before going further. Usually rear sensors are a bit easier to get to and can be swapped to verify.
I would also suggest they check the 4 pigtails at the camshaft adjusters (magnets) on the front of the engine, 2 per bank. In some instances oil has leaked through the adjuster and into the wire harness, causing substantial and very expensive damage to ECU and sensors.

jonUF02

The last temp thing is interesting. I has a slight vibration maybe 3 times in the past 4 years and 40k miles of ownership. Each time I got a catalyst code and cleared it. I believe each time I happened to need gas and stopped somewhere other than my usual Shell. Since then I avoid getting any other gas. Once I gassed up with my usual Shell 93 the vibration went away, and code didn't come back.


If the cat is choked, you would definitely get a catalyst code, and it would be pretty easy to remove the exhaust and see a totally choked car. Also you could just tap it with a rubber mallet and hear the broken choking bits rattle.