Am opening a new thread for an old issue because I want a fresh opinion. Apologies to all who have been through this. Also, this problem has several causes and maybe someone can save me unnecessary time and expense.

So, Symptom; Engine cranks over briskly but doesn't fire (anymore). No Codes. There are no problems shifting from the Park position.

History; The day starts with the engine requiring 2-3 seconds of additional cranking to start (new), but runs fine until it didn't (run fine . I had just left an automated car wash, engine on w/ no problems, down the block and pulled in to refuel. The first attempt to start (after refueling) had good starter RPM and the engine almost ran but would only idle roughly, very roughly, very, very, very roughly with no throttle response or power. Several attempts later (about ten) the engine would only turn over . . . I'd managed to get it to rough idle for about 30 seconds but it only turns over now. Vehicle Towed.

Actions; I've replaced the CrankPS with a Bosch unit (Fun) and read through some online trouble shooting info (which is why I went for the CPS sensor first Again, there was/is no engine light or fault flagged anywhere on the display but I haven't actually hooked up a OBDII reader.
4 Questions
1: Can I troubleshoot the CPS harness and plug w/ a VOMeter by turning on the ignition to "run" position? I did ohm out the old sensor, got nothing, and the same with the new sensor, no resistance shown.
2: I've read the ECU can be "reset". Does that need to happen after swapping a sensor like this?
3: Can I confirm fuel pressure (and therefore the pump) at the fuel manifold Schrader valve with only being able to crank the engine? (I have a schrader valve adaptor and a hose
4: I don't suspect water in the fuel but where's the filter? (just in case I want to check or change it
Bonus Question: Checking continuity on the ECU side of the BrakeLight Switch . . . . necessary?

Cars got 230,000 mi and all servicing other than my own has been done by Mercedes trained mech's.
I work as maint QC in the Propulsion Shop for a major airline . . . and I'm German . . . so I'm already handicapped here . . . And . . . I've got OCD with ADD . . . . . so everything's got to be in just the right order . . . but not for very long ; )

I appreciate all feedback
BW

 

The first thing I would do is read any logged codes.

It could be a number of things but my first guess and area of investigation would be the fuel system. I assume you filled the tank with fuel when you stopped for fuel. If the tank is less than 1/2 full it could be the fuel tank transfer pump. If full that would not be an issue. If you can check the fuel pressure and availability, I would do that. Again, the first step should be reading the codes.

 

Thankz Fatz, will locate my Code Reader and check for anything pertinent. I wouldn't think that fuel could transfer immediately from tank to engine on the first attempt to start. it's why I'm reluctant to suspect contaminated fuel, But there's always a first time so I'll check that too.
As I'd mentioned, I plan to connect a schrader valve adaptor with hose to a reservoir & crank her over to see what is flowing through the manifold. Maybe get an idea of how much pressure builds during cranking. I've Got a new battery to install as well just to eliminate that question mark.
Wanted to also mention I've done a search for previous mbworld threads for this same condition on both the W208 & 209. Didn't find duplicate symptoms but some helpful ideas.
That said, your input is much appreciated Fatz and I shall reply with resultz.
bw

 

I was not suggesting contaminated fuel. If you actually filled the tank when you stopped for gas, both sides of your gas tank would have fuel. There is a pump that pumps gas from the storage side to the side that supplies the engine. If your fuel gauge indicated less than half full and it cranks but w/n start it could be that the transfer pump is not transferring fuel to the engine supply side of the fuel tank. If you filled the tank, both sides will have fuel and the transfer pump is not a concern.

 

Understood you were referring to the tank xfer pump Fatz. I'm the one suggesting fuel contamination and related issues. It's just that this wasnt a sudden hard fail . . . the engine did try to run badly on my first start attempts and progressed to a no fire condition . . . . makes a case for fuel starvation . . . . the ignition is suspect too but im only 60/40 - fuel/ignition at this point).
​​​​​​ . Am here to learn my friend and the fuel tank setup is unknown to me, much appreciated! So I'm going after codes and if none shown then I'll check the fuel system at the manifold schrader valve . . . . Was almost hoping this problem would have been more intermittent or given a few . . . "Im reestarting I'm fine again" clues to help w/ troubleshooting : /
Thx again sir!
bw