560SL will just stop running
 

My 560SL has been in the shop for 2 weeks and they can't find the problem. Sometimes at low speed ( under 20mph ) it will just quit as if I turned off the ignition. Usually it will start right back up, but last time I turned it off for about 1 minute, it finally started after a 20 minute wait. It turns over normally, but it doesn't even try to fire. It has never happened when I've been going 35 mph or more and I'm guessing at the under 20 mph, but it is only at slow speed or stopped at a light. When it starts back it runs great. It is not time or distance related as it might go several days without incident. There is no warning such as a miss or stumble. When it starts back up its as though nothing ever happened. Perfectly normal until the next time it decides to stop.
Any thoughts will be appreciated. The shop that has it only works on Mercedes, and so far they can't locate the problem.
Tom

Most likely you are loosing fuel or ignition. When it wont start you need to check for spark. If you have spark check to confirm that the fuel pumps are running. This is a starting point on the tree of diagnosis. There are many branches to follow. Once you eliminate one of these two possibilities we can preceed from there.

unless you've replaced it i would replace the flywheel pickup for the ignition unit.these things have been falling like flies with exactly the symptoms you mention.

I'ts got to be spark related- if it was fuel then it would die slowly. Anything that has to do with ignition is the logical starting point.

Two weeks?
 

It would help if you would tell us what your shop has done. Hard to believe that they would not check for spark or fuel problems.

And, losing fuel pressure will kill a 560 as quickly as turning off the key.

Does this happen only when the fuel tank is about 1/4 full or less? In that case it could be a clogged fuel pickup screen.

I second this...plus it is cheap and easy to replace...try it out and see what happens.

just for the info of all,the fuel pump is kept alive by the "td" signal from the ignition unit,so when spark dies the pump stops.

Thanks for all the responses. The Mercedes guy called earlier today and said it is fixed !! The German owner of ******** Of Union, where I took the car, had been driving it whenever he could, to see it would quit on him so he could find the problem, and it finally quit running while he was driving it. Problem solved or so he says.
It was what he called the ignition module. It was actually what looks to me like the back half of the ignition switch. The part only cost me $20. and he gave me the old part. Labor was considerably more, but if the problem is indeed fixed, I'm happy.
Thanks again for all the responses.