Car is running rough and cannot figure out why

Tiny
DILLINATOR
  • MEMBER
  • 2005 MERCEDES BENZ C230
  • 1.8L
  • 4 CYL
  • TURBO
  • 2WD
  • AUTOMATIC
  • 206,000 MILES
The engine is running really rough, small amounts of black smoke occasionally exit the exhaust, it backfires when I let off the gas, and it feels like it's struggling. There are no codes and no check engine light or anything that would indicate that the car is having issues. My car has now been this way for almost two months. Please help!
Monday, September 28th, 2020 AT 2:13 PM

11 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

Black smoke and backfire usually indicates excessive fuel to the engine. The first thing I would recommend is to check the fuel pressure. Here is a link that shows in general how it is done. When checking pressure, pay attention to how quickly the pressure drops when you turn off the pump. If it drops fast, there could be injectors leaking.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Also, here is a link you may find of interest. It discusses the most common causes of a backfire condition.

https://www.2carpros.com/articles/engine-backfires-while-running

Let me know if this helps or if you have other questions.

Take care,
Joe

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Monday, September 28th, 2020 AT 5:25 PM
Tiny
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Thank you Joe! I tried testing the fuel pressure, and everything was normal. The weird part was that afterwards, I drove the car down to O'Reilly's, and it ran perfectly fine. It's still running fine and it's been about a week since then. I don't know why it's working now, lol.
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Monday, October 5th, 2020 AT 10:45 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

It's possible there was something causing an injector to stick and when checking, you allowed it to move. Hopefully, it will continue. If it changes, let me know.

Take care of yourself and feel free to come back any time you have questions or need help.

Joe
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Monday, October 5th, 2020 AT 8:03 PM
Tiny
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That could be it, but I also remembered that I used an OBD2 scanner and cleared the codes off my car, and that the first time I drove it after that was when it started feeling fine. I wonder if the accident caused the car to go into "limp home mode".
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Thursday, October 8th, 2020 AT 12:15 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

I didn't realize there was an accident. However, it is possible that an accident could cause a fault leading to limp mode.

Joe
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Thursday, October 8th, 2020 AT 6:18 PM
Tiny
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Yes, I'm sorry I definitely should have mentioned that earlier. It wasn't really a crash though. The outer end of the lower left control arm separated and fell apart as I was backing out of a parking space. (The fluid you see is just the windshield wiper fluid. The tire hit the bottom of the container and broke it when it bent inwards) https://imgur.com/gallery/ZZB5V2S
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Friday, October 9th, 2020 AT 11:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

That shouldn't have caused this problem. However, anything is possible. Have you checked to make sure nothing has come disconnected such as vacuum hoses? Also, have any new codes resurfaced?

Joe
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Friday, October 9th, 2020 AT 9:25 PM
Tiny
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I have not checked to see if any new codes have resurfaced yet, but all of the hoses are still intact and just fine. If the weather clears up I'll go and check it again with the OBD2 scanner.
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Saturday, October 10th, 2020 AT 2:32 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Let me know if anything is different. I will watch for your reply.

Joe
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Saturday, October 10th, 2020 AT 5:10 PM
Tiny
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Hey Joe,

Sorry I've been very busy lately trying to deal with my job, high school, and college all at the same time. I haven't really had the time to check it yet but I just wanted to update you so you didn't think that I forgot or something.
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Tuesday, October 13th, 2020 AT 10:56 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
No problem. It sounds like you have your priorities aligned correctly. The car can wait. Stay focused on what is important (your job and education).

Take care and take your time.

Joe
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Tuesday, October 13th, 2020 AT 6:12 PM

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