Im not much help without a wiring diagram to look at but does the ECM use a power up relay external of the ECU to send 12 volt power to wake up the ECU? Im thinking back to my DSM days or even the 109 relay in VWs would do something similar when they would start to die. fuzzy or burned contacts in the relay would give enough power to turn on the ecu but supply power was iffy and caused all kinds of random issues.

 

So those are the same questions I have. I have some wiring diagrams I downloaded for the sensor connections. I don't know what all might be missing that would cause that low voltage. I need to check some voltages on some other locations and see if I see anything similar. I just thought about a code I've been getting for a while.... code 1611-2 on the ECM. That code says "check supply voltage(1) of sensors, readout too small". I researched this sometime back and was led to believe it was due to me running the battery down by cranking it so much. I may have been mistaken to believe that. The more I think about it, the more it seems to be highly connected. The question still stands... what's the root cause.

 

 

PROGRESS - but not total success... here latest.
Went old school with my Simpson 260 meter measuring ohms from the cam sensor supply wire (pin 3 at the sensor itself) to ground. I had about 70 ohms to ground. That seemed low to me and I suspected a partial short to ground somewhere. I started moving wiring harnesses around and disconnecting other sensors one at a time while watching my meter. No luck. But then I thought about the throttle pedal (B37) - which had been my issue from the start. I removed the pedal and the 70 ohms went to infinity (no short). I then checked power on pin 3 at the cam sensor and it was restored to 5v and the car cranked right up!!!!!! Wonderful, I'm back to where I was 4 weeks ago

Now then, I have to solve the issue with the pedal which is puzzling. When looking at the pedal on the wiring diagram Its hard to know what it really is. The picture causes it to LOOK like its more than a potentiometer - meaning it looks like a Transistor symbol indicating some sort of electronics inside. My wiring diagram is fuzzy so its not real clear to me what it is. Here's what I can say...The pedal has 2 sensors built into one, labeled #1 and #2. There are 5 wires and pin #1 on the pedal is +5v. Pins 3&4 are the signals for sensor #2 and pins #5&6 are sensor #1.

Without knowing what's inside the black box its hard to know how to test. But making assumptions that it could be 2 potentiometers inside I made several checks on each sensor. I also got the other bad pedal and did the same. I'm not going to try and document all the combinations here but the bottom line is:

1) While disconnected on the bench, moving the pedal produces NO ohm variation from any pin to any pin. (on either sensor on either pedal). This causes me to believe that the sensors are not potentiometers... but I could be wrong.
2) Resistance from associated pins of sensor 1 and 2, on both pedals, are not the same. Since I don't have a known good pedal to compare it to, I don't know what the readings are really telling me and if one is better than the other.
3) I've posted a photo of the wiring diagram.

So questions going through my mind, given that my problem started with the pedal failure (or at least seemingly) is:
1) How does the pedal work. Is it simple potentiometers or something else, like pulse train or pulse width modulation?
2) Why did buying TWO used pedals result in the appearance of correcting the problem but then leave me on the side of the road within minutes of replacing them? Note that the last pedal apparently failed in some manner that drug down the sensor voltage to 2.3v.
3) Is the pedal (any of the 3) really bad or is it something connected with wiring or the ECM? Although the two I have here are reading differently and I don't have a known working pedal at the moment to compare them to.
4) Is it possible that I purchased TWO sensors off ebay that somehow do not match my car ECM and they are failing? Note that the pedals I purchased SAID they fit my car and they look identical but that's not 100% guarantee. I'm confident that if I order another used pedal and put in on that it will work. I'm equally confident that 3 minutes down the road it will fail on me.

So that's where I am guys... this thing is kicking my butt but I'm not giving up

The secret is somehow connected to this pedal... just don't know what it is.

 

Good job your getting somwhere. I know for a fact with VW diesels the pedal from a gas car wont work although they look identical. Can you see what pedal position is with key on using torque pro or similar? I would compare your pedal part numbers and confirm your dealing with the CDI pedal.

 

For those who've followed and helped on this, I wanted to give an update.

I got her running!! Put the new Pedal on it and it's running. I've been watching the pedal signals on the scanner scope while exercising the pedal up and down. The two sensors don't appear to be opposite each other, as some told me, the run together up and down the range. All codes are gone for the moment. After all I did, It's impossible to reverse engineer everything that might have gone wrong on this car, as a root cause. My best guess is that the oily substance I found in the ECM connector created one or more shorts in the system and caused the pedal to go bad in the first place. Its hard to know what the next issues were but two more used pedals off ebay also failed. The 2nd one failed and shorted internally enough to pull the sensor voltage low (2.3v). This led to the Cam sensor not functioning and prevented the car from starting even though it would crank. Over the journey, I had the ECM rebuilt, put new Cam and Crank sensors on, and I purchased an OEM pedal on the 3rd try to make sure I eliminated that from the equation.

I changed the oil cooler gasket that's been leaking for a long time, what a pain in the butt to change. I'll never be able to prove it but I feel there's a likelihood that the leaky oil cooler contributed to oil getting into the ECM connector because the oil traveled up the wiring harness from the engine compartment. I didn't realize the oil leak was as significant as it was but I feel that all the excell oil in the engine compartment may have been the source of oil that traveled up the harness.

I made several mistakes along the journey as well that contributed to the length of time it took to resolve. I listened or took advise from folks who were trying to help but may not have the experience to provide the guidance. This was my fault, not theirs. One example of that is some folks said the Cam sensor would NOT prevent the car from starting. That was wrong. It will ABSOLUTELY prevent the engine from starting. Micha / AF1 Rac was one of those that gave the right advice on this. I should have spent more time working that angle than I did. The story I told myself was that since I had changed the Cam sensor that it must be something else. Ultimately, getting over that stumbling block got me on track to solving the original problem, the pedal. Other mistakes I made was not taking my Scanner more seriously. I dismissed certain indicators that cost me time and money. I should have also gotten wiring diagrams sooner than I did. These are not the easiest things to come by but they proved invaluable in helping me understand what I couldn't see. While I do not own a STAR scanner, my Launch scanner did (and does) a good job typically and was giving me the guidance I needed. Over the threads I engaged in, there was advise ranging from the main battery, aux battery, fuel pressure, battery controller, front or rear signal acquisition module, jumped time, crank sensor, and more. Again, this is my fault for not being more diligent about following the signs I was given. I realize that, like me, folks who lend help on these forums are all trying to do the right thing, for no money, and I appreciate that.

I haven't had to do very much to this car since I've owned it and it now has almost 300k miles. If I were to give advise to those who are DIY types, I would say
1) Purchase a good scanner and learn how to use it well. Anyone considering this should inquire of the Mercedes community for suggestions of the minimum scanner to get. If you pay $1000 for one, it'll save you $5,000 over the long haul. BTW, good professional scanners also have the capability of being an Oscilloscope and DMM mentioned below. So one good purchase here could avoid the need for others.
2) Acquire workshop manuals of your car class and make sure you get one with wiring diagrams. No telling how much time & trouble this will save you if you plan on owning the car a few years like I do.
3) Get a decent DMM (digital multimeter) and I also suggest an old school analog meter like a Simpson 260. Get an Oscilloscope unless you get a scanner that has one included.
4) Get back pins for stabbing into the back of connectors easily to check voltages.
5) Learn how to take all these and perform good root-cause diagnostics to avoid being a parts changer (I did this too much in my recent issue).

Ok, that's my input for this evening... thanks to all those who helped me on this journey!