Originally Posted by TimFreeh

Rear SAM controls the tank mounted fuel pump. Non functioning rear SAM would disable the car.

I'm not sure about newer E-class cars but in the 2005-2006 era SAM's do require version coding when installed however its not the full-blown online phone-home-to-the-father-land-for-authorization SCN coding that's required for emissions or theft relevant parts the newer models require. It can be done with a stand-alone Star system and it's quite easy. I've replaced front SAM's with junkyard replacements and the process was a menu-driven 10 or so questions/answers and then save to the replacement SAM.

The RPM signal in the CDI's is generated by the N3/9 CDI control unit and reported on the CAN where its picked up by the instrument cluster and reported to the driver. The thing that I keep focusing on is why is the CDI ECU apparently reporting an RPM reading when the engine isn't running? If you can get an RPM signal on the tach without starting the engine with the key in position 2 that's a good sign the ECU is highly confused about it's state of affairs.

This is where things get almost impossible from a diagnostics perspective. Is the ECU confused because 1) its getting bad/confliciting data from 1 of the 24 sensors that feed it information to make decisions 2) a problem with it's power source or 3) The ECU is failing and losing its mind.

And of course it's not an either/or situation - it could be some combination of 1,2 and 3 of the above.

You mentioned your independent Tech verified the crank and cam sensors are good. How did they do this? Did they put a scope on the relevant pins and look at the waveforms? Or did they just look for codes associated with those sensors?

If I were doing diagnostics on this car I think I'd try to scope the crank/cam sensors and see what kind of waveforms were on the inputs to the crank/cam sensors when the car was KOEO and exhibiting RPM bouncing round/no start symptom. You should't see anything on the input lines of either of these sensors with the engine off. Bad data or noise on these lines could confuse the ECU.

It would also be helpful to use the real dealer-level STAR tool to check for codes/data from the N3/9 control module. The after market scan tools are pretty good but they generally don't get to all the data or codes that the full-blown dealer tools can access.

I'm sure the OM61X guys are loving this thread!