So I'm leaning towards crank sensor but I'm far from certain at this point. I went out a couple nights ago and at about 11pm hopped in the xfire (2006 limited with the tvt265 kit). Turn the key to "on" and let it prime the fuel pump for a min (I only drive the car about once a week), then go ahead and give it a solid flick and it cranks right up. As soon as it's running, however, it stalls, and all power is gone from the dash. Tried to crank it again to no avail (dead, zero power to anything from what I could tell, no starter click or anything).

I turn my headlights on and after a fraction of a second they click on and it's like the old girl got water thrown in her face, all power came back across the dash and she cranked back up fine. Took her for a drive with no problems at all and haven't had a problem sense.

I've had random crank sensor problems on other vehicle so I know they can be beyond intermittent but I'm not familiar enough with the starting circuit on the Mercedes to know if this is something that could happen. If it throws a red flag to anyone out there please chime in!

edit: Once she cranked up fine there was no CEL or anything, don't have access to a scanner to read any hidden codes.

 

I'd check for corrosion on the battery terminals, battery leads and grounds first. May also want to check the battery leads for any internal damage/corrosion.

 

Battery is my choice. Woody

 

Thanks for the quick replies, The battery is about a year old and had no problem starting the vehicle (and never has). I checked all my leads to the battery but not at the starter, I run aftermarket audio so I have a stout battery, upgraded terminals, etc and take good care of the battery side just because I don't like the possibility of ruining an amp.

I'll be switching amps in the next week so I'll triple check all my wiring when I do that and be sure of my floating voltage since the car rarely gets driven.

 

Ok so the car is still acting up, I went ahead and cleaned my terminals again and checked the wiring (still haven't gone to the starter but I don't see a reason to now.

The behavior: a couple of days ago I ran out to grab some dog food, 15min drive. No problems at all but when I come back out to the car it cranks up and immediately dies, this time though, it retains 12v power through the dash and headlights and I can crank it back up with no problem. But, it dies again. The car will crank up and almost come back down to idle when it's like someone just shuts the key off. After starting it and watching it die about 5 times it finally stays idling and I drive home with no issues at all.

--this is where I pulled the terminals and cleaned them again, they were a little corroded but not even close to enough to cause a problem.

This morning I hop in the car (to go to a job interview of all things) and it immediately dies again, and this time, like the original, it completely loses power across the dash including the headlights. I have no radio, no lights, no dash lights or lcd readout and absolutely no response to turning the key. I left the car as it sat and took the jeep to the interview.

Just got finished checking voltages and as the car sat remember I had zero power inside, but I did get a dome light when I opened the door this time. Solid 12.5v (ish) at the amplifier, 12.5v across the battery as well and I also checked at the fused block beside the battery(Engine Fuse Block),and all was good there.

After screwing with it and checking power at a few different places I go open the car door and voila...power again(no idea when it happened as I was under the hood). I crank the car up about a dozen times and it behaves 100% normal. The clock and my radio settings had all reset though so power was definitely lacking.

At this point I am lead to believe it's something from the "Engine Fuse Block" to the "Splice Block 100" (glad I found the online wiring diagram, I at least know what I'm looking at now). Next time I lose power I'll be able to verify that the problem exists here by probing the Splice Block and before/after if necessary


So, more of an update than anything but if anyone has any input I'll gladly accept.