TherealJT

This one has me worried. Was out for a drive tonight and did a couple red light blasts and the car felt like it was down about 100 hp - it was way slower than usual. No alarms, no smoke, no fluid loss, nothing abnormal, no excess weight, sport mode engaged, ESC off, A/C off. Anyone ever experienced this? Is there some kind of safe mode, or limp mode that can get engaged? This wasn't a slow gradual drop in power over weeks and months - I had it out last week and it felt normal. But tonight, it suddenly had far less power.

WIN ER

Maybe just a heat soak? Or got some crappy gas filled? Anything else would be indicated on your dash.

TherealJT

It felt more electronic than mechanical. The torque was okay off the line, but then it just wasn't accelerating. It felt exactly as if I was only giving about 50% throttle.

Think I might try lifting the battery terminals to reboot the system.

Any other thoughts? Konigstiger?

TherealJT

I lifted the negative terminal and left it for about 20 mins but it didn't seem to reboot the ECU. Do you have to lift the positive terminal as well? Drove it again today and it felt the same - low power.

Would like to avoid taking it to the stealership.

Bad gas is definitely a possibility, but it's not hesitating or idling rough or anything, it just won't accelerate.

WIN ER

Disconnect both terminals for a couple of hours.
apart of the ECU
It could be either knock sensor or bad spark plugs, in last case you would feel it at idle as well.
Good luck!

TherealJT

Here's a thought. What about the variable valve timing? If the timing isn't advancing properly it would greatly affect hp. Anyone experience issues with this?

Chevota

I have the same problem! 2016 E550 Coupe which sometime over the last couple months lost a ton of power! No codes, nothing abnormal, just less power across the board.
Originally I thought the intercooler pump failed because they say expect failure about this time in it's life and my intake temps are high, but a new pump changed nothing at all, same temp, same low power.
To give an idea on power I had a '13 E350 before this and that's what it feels like. One member suggested I may have a leak bleeding off boost, but I can't find anything. To check for that I did a visual and felt around, then I pulled off the air boxes and put my hands over the two intake pipes. At idle it just about sucked my hands in! Not the best test since a cracked part or loose/missing hose clamp in the system would hold a vacuum but vent under pressure. So I think tomorrow I'll (try to) pump shop air into it with the eng off and see what that does.

But whatever it is it sounds like have the same problem... So please share if you find it and I'll do the same.

Siegmann

OP, did you ever figure this one out?

TherealJT

Yeah it was gas - not bad gas, just me not realizing how much power is lost with lower octane gas. The knock sensors are very sensitive on these engines so it will pull timing to prevent knock. I took it to the dyno and you could visually see the timing being pulled back during the pull. I came back a month later with 95 octane gas and the power increased to what it should be.

Chevota

Fascinating. I've never had timing make much difference so I'm curious how much difference we're talking about. Not 100hp obviously but enough that you thought it was 100 is pretty extreme. And of course what ambient air and intake air temps were during each test because imo that makes a bigger difference so you have to consider it. Not sure if you recorded those but I'd imagine the dyno shop at least had the ambient?

Fyi I tried much higher octane on my car to see if the issue was timing related, it was not Never found my issue, probably never will...