xjmoe83

I don't recall mentioning the reinitializing of the crank sensor, but the way I have done it in the past is with the MB Star Diagnosis machine, "Resetting rotor adaptation". Without the Star Diagnosis machine, I'm not sure how to go about it.

Can you verify the coolant temp sensor is working and accurate? Also, make sure the air box is properly installed and the main, rear seal (to the air box is properly installed.

Also, check fuel pressure. Should be about 55psi. While you are there, take a fuel sample in a clear bottle, take notice to any separation (water in fuel)

Without checking it out with the computer, I'm not too sure. Heat should not be an issue. The ECU's on these are not that problematic imo.

the1donald

Perhaps you could explain your logic on the fuel press and coolant temp?

xjmoe83

You mentioned you were having issues with the coolant temp sensor. The coolant temp sensor has the ability to change the fuel trim (rich/lean). It's very easy to verify that it is accurate, so check it.
Same goes for fuel pressure. If the correct amount of fuel is not being delivered, the engine would obviously run different (lean) and could give you the rough running condition.

I'm not saying those are the problems, but you need to check the basics and any previously know problem that could be causing this.

the1donald

XJmoe83: There seems to be a lot of esoteric idiosyncracies with these Mercedes cars and I'm not sure what to expect. I won't argue with your logic, but you said the same thing about the crank sensor job. The coolant temp sensor is located in back of the engine next to the crank sensor on this model.The crank sensor job was a real PITA. Taking out the temp sensor would be even worse as some coolant would have to be drained. I have learned that this is a dual sensor-with one element driving the temp gauge in the instrument panel and the other to the ECU. Wouldn't the temp reported from the OBD indicate the ECU sensor status? As long as the instrument panel gauge and the OBD data correlate, and behave normally, shouldn't that be adequate verification of the temp sensor/s? The temp gauge did indicate normal temps, but I didn't read the OBD temp before this catastrophe. As far as the fuel pressure, as I said, I'm not a pro with access to all that equipment(and know how), but I'm willing to learn. The fuel pressure is something that I'll have to research in WIS. It sounds like a major ordeal, but it is something that I will consider. But back to the other sensors. You may recall that I mentioned the horrific air filters that appear to have never been replaced in this 7yr old car. I dumped about a cup full of dirt, sand, leaves, bugs, etc. out of the air filter housing as I dismantled the engine covers. It was very discouraging to see this. Do you suppose that the air filters were so badly clogged(and they were terrible), that the sensors could have been damaged as the ECU tried to compensate for lack of air/oxygen. I'm thinking that the MAF sensor may have overheated as well, from lack of air flow? Considering all of this, there is one other thing that has been haunting me - When I took delivery of the car, I recruited a friend to drive it home for me. When I gave him the keys, he immediately rev'd up the engine to near red-line(over 6K) for several seconds. I yelled for him to stop but he was an idiot who has no in-depth knowledge of cars, and certainly no appreciation for the delicate state of a used Mercedes with so many unknowns. I had scanned the OBD before the purchase, but not again until about 50 miles later when everything went haywire. Thanks for all your time, and I appreciate any detailed info and especially any knowledge you will share.

the1donald

Can anyone explain the up-stream O2 sensors reporting 0V/0% trim but doesn't throw a code. I'm scanning with "OBDcom" scan tool/software that I purchased several years back. The down-stream sensors report a typical voltage between 0.4 & 0.8V. I realize that these 6-wire up-stream sensors are more complex and sophisticated than the average 4-wire sensor. I found other posts indicating specific codes for too rich and too lean. I've scanned another 08 C300 which reports the same-0V/0% trim through my scan tool. Both cars seem to be running OK, so I'm guessing that this is a Mercedes thing. Would be grateful for any specific tech info on the Mercedes up-stream O2 measurements/reporting.

jpminou

Did u changed ur spark plugs?
I had a problem with o2 sensor and replacing spark plugs with new one fix it. So maybe give it a try.

the1donald

What I'm was getting at is maybe there's nothing wrong with the O2 sensors. It's not throwing any codes. Just the up-stream voltage as reported from my scanner is 0V. Maybe it's just the software of my scanner. Was hoping someone out there might have some more in-depth MB knowledge.