amira

Hi all the 126 gurus,
I'm new in this thread and wonder if I can be furnished with advice as of the following fuel supply problem.
It is about my 1986 560SEC. I own it for the last 6 years or so. The car is original, 150K miles. I'm the second owner and it is pristine.
Sometimes (totally random) when I start the engine it start and die immediately. It takes it less then a second to die and it would never start again.
I have installed new original fuel pumps, still the same.
I installed a new original accumulator, still the same.
I replaced the fuel pump relay and bingo(!) the car started and it runs absolutely fine. It takes it few days and it happens again - the car would not start...till I replace the fuel pump relay. The strange thing is that the replacement relay that I use is the same one which seemed to be faulty last time it happened. The same phenomena happens again and again every few days...and sometimes three times a day. Frustrating! I still use the same 2 relays for the fix. (Btw - when I try to take the "faulty" relay out and put it back the car wouldn't start so it is not any loose contact that I could think about.)
Any ideas would be much appreciated.

Gamer_S

This sounds very similar to the heat related sensor failure my 560SEL had, not the same symptoms, but very similar in principal. Could be a heat related component failure. Meaning whatever the faulty electronic part is, it doesn't malfunction until it has reached a certain temperature threshold, and then once it has dropped below the failure temperature it goes back to working. High probability it's a sensor that's failed/failing.

amira

Thanks for the input. I'm not sure that the temperature is a factor - The problem occurs in a variety of temperatures - after few weeks of storage....after a long distance drive....after a short distance drive etc'.. It is totally random.