R170 cut out and no start

[nigxls]

Well picked up my new car yesterday and drove 30 odd mile before stopping at services for fuel. Did about another 30 mile and the engine cut out on the motorway. Managed to coast to the hard shoulder and engine was cranking but not starting.
Got recovered the last 60 odd mile late last night and this morning tried the car again, still no start. Re soldered the K40 relay and disconnected the battery for about 15 mins while I was doing this. The engine then started but cut after about 20 seconds.
Now it will start sometimes, maybe 1 in 10 but cut out almost immediately.
Guessing the Crank sensor possibly as when cranking I don't get so much as a flicker from the tacho ??
Any thoughts?

 

[grober]

A K40 HOWTO reminder https://youtu.be/70b-LJsbFqk Did it show signs of solderered joint breakdown? CPS seems a good shout next- other possibility would be a dodgy ignition switch - Is the k40 getting power on ignition switch on when the car is dead?
[YOUTUBE HD]70b-LJsbFqk[/YOUTUBE HD]

 

[grober]

A K40 HOWTO reminder https://youtu.be/70b-LJsbFqk Did it show signs of solderered joint breakdown? CPS seems a good shout next- other possibility would be a dodgy ignition switch - Is the k40 getting power on ignition switch on when the car is dead?
http://www.benzworld.org/forums/r170-slk-class/1263021-k40-relay-circuit-associated.html

[YOUTUBE HD]70b-LJsbFqk[/YOUTUBE HD]

 

[nigxls]

Thanks Graham, I've not checked for voltage at K40, just popped it out and re soldered it. Joint looked ok but I sucked the old solder out and put new in. The K40 had been replaced with a new part some time ago by the previous owner, as had the Crank and Cam sensors but I don't think he used Bosch items so I have ordered a crank sensor, should be in this afternoon. Will keep you posted.

 

[nigxls]

Ok so new crank angle sensor fitted and nothing has changed.
I can smell fuel so I'm guessing I have an electrical issue.
Just about to pop the plugs out and have a look to see if I have a spark.
Update, I have a spark on nos 1 and 4 plugs, although a bit yellow in colour, plugs were smelling of fuel however but not wet. Electrodes were quite black.

 

[nigxls]

Should read plugs 1 and 3 have a spark.

 

[grober]

If its the M111 engine it has the lost spark system where two plugs are are fired at the same time by the same coil 1+4* and 2*+3 This can happen because one of the two cylinders is on the compression stroke coming up to fire while the other is on the exhaust stroke with the exhaust valve open. Sounds as if the supply voltage to the coils is down.
* coil position

http://www.pelicanparts.com/techart...INE-Spark_Plugs_Wire_and_Coil_Replacement.htm

 

[nigxls]

The battery was in fine fettle at the start of the day, was starting to get a bit lazy by the time I got to this stage so low volts is probably right. I'll try it again tomorrow when the battery has had a good overnight trickle charge. Thanks again.
Not sure if I also have an aftermarket alarm fitted, certainly doesn't look standard to me, I have two ultrasonic sensors on top of the dash and a horn unit bolted to the top of the front N S wheel arch?? May also be an immobilizer ??

 

[nigxls]

Quick update, thought I would connect the battery back up and give it another go and voila she started first time. Disconnecting the battery must have deleted whatever code was holding it out. Seems like it was the crank sensor after all.
Battery back on charge again now until the morning when it's service time, I just hope it starts again
Cheers Graham