PeachParts Mercedes-Benz Forum - View Single Post

MB-Dude · #28 11-15-2007, 10:11 AM

I changed all the small diameter milky-white plastic tubing as it was getting pretty brittle. During the change-out, I came across some interesting things. Picture #1 shows one of the vacuum lines I removed – you can see oil in the line! This oil is still viscous and can move along the line. Needless to say, this should not be. As I dug deeper into this particular vacuum line, I found the line had numerous sections with oil in it. I became very encouraged as this line goes from the Bank 2 intake manifold to the Bank 2 MAP Sensor (MB p/n: 011.542.06.17).

I removed the MAP Sensor and, sure enough, there was oil inside the MAP Sensor vacuum port. Picture #2 shows where the oil was found. By now I was real excited and thought for sure that I’d found ‘the’ problem! A quick call the local dealer told me the sensors would not be available until the next day. So I decided to swap them around, in hopes the original O2 Sensor problem would move.

When I removed the MAP Sensor for Bank 1, I again made an interesting discovery – the potting mixture of the sensor had somehow become soft and deteriorated. Picture #3 shows the deformation of the potting material as compared to a ‘normal’ looking sensor. Could I have two sensors bad? At a minimum, one is definitely not good and the other may be going bad.

Over the driver’s front wheel, next to the throttle potentiometer and Body Acceleration Sensor, there is another one of these Vacuum Sensors, though I am not sure what it is used for. However, it appeared in excellent condition. So I swapped this good one with the one that had oil in it. My goal was to see if the O2 Sensor issue moved or went away.

Much to my dismay, after swapping the MAP Sensors around and replacing all the small diameter milky-white plastic tubing, there was no change in my O2 Sensor symptoms. Zero… null… nada! The engine does (subjectively-speaking) run a little smoother – especially at cold idle. But the Bank 2 O2 Sensor still reports zero output, and thus, the computers are ‘Not Ready’.

The vacuum lines needed to be changed – no question. And the Bank 2 MAP Sensor was certainly not working correctly with oil in it. I still do not know how/why the oil is in the line, but as the pictures show, it was there. And the Bank 1 MAP Sensor, with the deformed and soft potting mixture is going bad, if not already defective. So the day was not a complete loss.

But this O2 Sensor problem is getting quite quite frustrating. I am now to the point where I do not know what to do next, in terms of repairs or diagnostic work. Technical information is virtually non-existent, Mercedes is zero help and the 'latest' R129 Technical DVD (which I just received) provides no information in solving this problem. I am mentally prepared to expend the $$$ for a replacement ECU, but not as an experiment. I want to be certain an ECU replacement will solve the problem as that would be a very expensive troubleshooting item since one cannot return special order parts. Maybe it’s time to simply give up on Mercedes and cave in to what people have been telling me for years - that they're crap.

I suppose I’ll continue for a bit, but have no idea what to try next. Someone out here must have some knowledge on ‘how’ the Oxygen Sensor system ties together. I cannot believe the Mercedes repair philosophy is simply to throw parts at the problem – at the customer’s expense – hoping one of them will fix the problem. (If it is, then this certainly is not the motorcar marquee I want to be associated with.) Please, if anyone has ideas, suggestions, etc., I’d really appreciate hearing from you.

Cheers,
Jeff