Another female desperately needs help with..... ML320
 

I have a 1998 ML320 with 100,000 miles on it. The check engine light came on recently. I took it to a mechanic and he read the code and said there are several instances of engine misfires howver he was not sure if that was causing the check engine light to come on.
He changed the spark plugs and air filter. I also recently replaced one o2 sensor.
Now my truck is running badly, when idling it is really rough, sometimes there is a rattling sound that seems to come from under the car and the check engine light is still on. The mechanic thinks the rattling might be because of the catalytic converter or fuel pressure?? He says at this point he is just guessing because he cannot tell for sure what the problem is. I don't want to keep paying for useless repairs. It is getting really expensive. Any suggestions?

Crawl under the vehicle and put your ear under the catalytic converter. If that is what is rattling, you will be able to tell. Just don't touch; it gets real hot, real fast.

Hey. Best thing you could do it take it to a Mercedes specialist independent mechanic. Those guesses being made are really expensive (and a real pain). There are experts who can test to figure out exactly what's wrong and replace only the necessary parts. Good luck and enjoy.

Yes, it is sometimes difficult to diagnose a check engine light over the internet. Do you know exactly what the codes that were pulled are?

Whats with the multiple postings?

Find a boyfriend who's handy around the car!

That's who I take the car to. Which is why it is so frustrating to hear him say that now all he can do is guess!

No, he did not tell me the codes. He just said that the codes showed that the engine was misfiring. It did not show problems with any specific parts. I am planning to take it to Autozone and see if they can give me the codes.

I was not sure which forum to post to and did not think that ANYONE would have an issue with two postings.

As for your advice, all I can say is............Thank-you to all of you who took the time to be helpful!

From what I hear ML's are not Mercedes finest effort. With 100K on the clock it might be a good idea to start shopping around for a replacement. Your probably just getting a taste of what's to come....

I wouldn't sell off the car just yet at 100k miles. Sure there were teething problems, but I wouldn't necessarily put off the vehicle solely because it has 100k miles on it. If you could ask the mechanic about the specific codes he pulled it may be easier for someone here with more knowledge on your specific problem to narrow down the possibilities.

Since the "expert" MB mechanic can't seem to tell what the problem is, I can't do much worse by guessing.

Things that are in need of replacement at 100K...spark plugs at least. You may also have a bad coil or two. The tech can check these easily.

Also, a bad MAS and an ailing fuel pump can set off misfire codes (as was in my case).

Bottom line is this could set you into just under $2K if you let the tech just start replacing all of what I mentioned. For starters, if the plugs and MAS are original, I would get those done first.

Did these symptoms just start out of the blue, or was it a gradual degeneration in performance?
How did the plugs look when he pulled them?
What made him think that one O2 sensor was bad?
Are you using the correct grade of fuel/using a quality fuel?
You say it idles rough...what about when you accellerate/drive at a steady speed?

Only one person has hinted at what seems fairly obvious to me, that her mechanic lacks necessary skill. A trained Mercedes mechanic should be able to provide a correct diagnosis, or at least much better than what she got from this mechanic. I admit that it can sometimes be difficult to find a mechanic both skilled and honest. Also, I wouldn't be surprised if G-benz's diagnosis is correct.

Mike

I talked to my mechanic and he said that they did not note down all the codes because there were so many and they all basically were that cylinders 4 and 6 were misfiring. So they changed the spark plugs, thinking that would fix the problem.The car was due for a service anyway and it needed to be done.
Since the CEL is still on, I took the car to Autozone and when they read it the only code that came up was 'P0306, Cylinder 6 misfire detected'.
I talked to the mechanic again and he thinks that the catalytic converter on the driver's side might be causing the problem and should be replaced.

The check engine light came on a couple of weeks ago, till then the car was running fine. The O2 sensor was changed a little over a year ago when the CEL light had come on then. I have only used premium fuel in the car. The car runs fine at a steady speed but occassionally I can feel it "skip a beat" (probably when one of the cylinder misfires!)