Hey everyone. New here, just picked up a 2014 E550 4Matic with 80,000 miles as my daily driver.

I’ve recently developed a “thump” or a slip from the rear end when I’m pressing the gas 35-50%. This happens intermittently in all gears, while holding a gear, and never during shifts. I never have issues at WOT, so I’m a little confused. Sometimes the thump happens 2-3 times until I let off the gas.

From the advice of this forum, I had the car in for a fluid change at the dealer to see if it was simply just a fluid issue, but no change.

Before I take this back in, has anyone experienced this before?

 

So you had the rear differential fluid changed, correct? Did they check the drive shaft while under there, and I assume you asked them to check out the thump noise? What did they say?

 

Probably the rear driveshaft flex plate.

 

I should have clarified, I had the transmission fluid changed to see if it would correct the issue. I have the car scheduled to go back in, but they are 4 weeks behind in their service department... so I have to wait.

I was able to easily replicate the issue when I hold the car in 7th gear on the highway, and give it 50% throttle. I feel several slips from the driveline in a row, which feels almost like hitting bums in the road. When I floor it, no slipping occurs, and when I shift gears, no issues. You'd think if it was an axle, transmission, or clutch, it would be slipping at WOT more than anything. The axles don't appear to be leaking, but that's not always an indicator that they are good.

I have yet to look at the flexplate on the drive shaft. Could this create a bind at only moderate torque, and seem fine when all the torque is applied to it?

 

Could it be the thump you're feeling under load is the TCU releasing the TORQUE CONVERTER CLUTCH ?
These transmissions have multiple level of TCC, no longer just a single clutch.

 

I wouldn’t believe so as sometimes it will have multiple slips at a time. If it’s a torque converter issue, it’ll probably cost a fortune to fix it.

 

So it appears that it was not driveline related at all, but instead misfire-related.

I had opened it up to pass a string of cars on a back road when the car started stumbling and the CEL began flashing. I am mid-pass at this point, so I'm committed to it, and end up just powering through it and pulling off afterwards. I shut the car down for a few minutes, start it back up, its running smooth as glass, no CEL. I hook it up to my scanner and find that the CEL was a P0303. I order a set of spark plugs and one coil pack (just in case), and as soon as I pop off the insulator on the passenger side, I see the coil packs are wet from the back side. I popped all of them off to find that they all are drenched in oil. I get more curious and start unplugging the injectors, but they were dry, and so was the whole driver's side and main ECU (whew).

So I follow the the harness down to the cam sensors and unplug them... bingo, that's the issue. All 4 of them were leaking, as well as the solenoids. I had no idea this things had oil harness issues, and think I've only ever heard of this issue with one other vehicle in the past. I've ordered all new Cam Sensors, Cam Solenoids, and will report back once I get it back cleaned up and back together. Although I'm a little upset that the M278 has such a large weakness, I guess I'm somewhat elated that I figured it out before it got worse... I priced a new harness, ECU, all new coils, injectors, and O2s... it was $5,000 in parts alone, instead of $450 worth of parts and expedited shipping from FCP Euro.

 

I'm glad you found this before it was "too late"

And, yeah, the M278 has this issue also as a number here can attest