I have been having intermittent starting problems. In brief:-
1) Started about 3 weeks ago - car won't start (merc 1999 e240 - location UK) when petrol was low (red on).
2) Topped up petrol - about 2 gallons - tried car and it started. So thought must be out of petrol but found out on forums that when red light is on there is still about 8 gallons in reserve.
3) Carried on using car - car failed to start another day while it showed 3 gallons - opened petrol cap air came out - started car. Thought must be some problem with air in fuel tank (note I'm not a mechanic so I can only assume things as per my knowledge - I am an IT expert so mind my logical thinking)...
4) Another day car won't start on 5 gallons - son kept on trying and flattened battery! Called AA (very nice man - joke for UK only) jump started car. SO THOUGHT IT'S been battery all time since low battery can cause all sorts of problems...
5) week later car won't start on 7 gallons - DAMM MERC - son tried it few times but waited about half hour each time GAVE UP and called AA. AA guy comes and tries and guess WHAT car starts!
6) Took it to our work place (college) we have motor vehicle tutors (full garage facilities) - asked tutor to replace Fuel Filter.
7) Fuel filter replaced by tutor - he phone me and says it won't start! Tried a few times and left him to it - he rang other mechanic mates of his also found that no power to fuel pumps... I told him about when before I topped up petrol it would start - tutor gets angry! Left him. Later after half an hour he phones it's started! Run over how? Eh - did nothing just looking around then tried it! I said might be faulty relay - he said might be get it from MERC DEALER. I said not yet I just want to see if it was filter that was problem...
8) Now I have had the car starting OK since Friday - Friday started car 3 times on separate occasions - SAT started car once - WILL keep trying/checking all next week. Hope to GOD it's all ok now. Will post any news since it may help the next guy...

PLEASE can anyone else who had similar problem post here plus any tips...

Another question can I get a Key Fob from eBay and programme it to work with my car - can anyone who knows how to programme these fobs please help (maybe a merc mechanic who has a soft heart for us poor people with merc problems)...

 

Would you have a spare crankshaft position sensor in your tool box?
Blue

 

Don't have a spare one (CPS)...

 

Just done a test... It's taken me over 2 weeks to locate the CPS (and think it's that at fault)... Got confused with some American versions of Mercs and different models showing the CPS looking much different to mine. Used Autodata to locate the postion... Still wasn't sure since my mechanic wasn't sure if it was the right part we were looking at... Decided today to take this chance UN-PLUG THE CPS (THE PART THAT I THOUGHT WAS THE CPS) and try to start the car... Turned the key WITH SWEAT POURING DOWN MY FOREHEAD (THINKING WHAT IF THIS PART IS NOT CPS AND SOMETHING OTHER - I COULD DAMAGE THE ENGINE) to start potion...

Yes start position and closed my eyes expecting to hear some sort of a BANG (note I am not a mechanic so you can understand my thoughts)...
Car did exact same as when it would NOT start - HENCE FOUND THE PROBLEM!!!!!!!!!!!!!!!!!!!!!
Thanks to ALLAH/GOD I found the problem AND NOW I CAN HELP OTHERS!
Will order a new CPS and test car if still any similar problems then I would need to either change the plug that fits the CPS or just make it a more tighter fit SINCE I KNOW IT'S THIS AREA THAT'S AT FAULT.

Let me now explain why car would not start on low petrol.
Basically one fills tank to requirent and goes on his/her journey.
Come back and petrol is lowish - car is very hot near all engine areas as they are.
Temperature drops from one extreme to a certain temp THE CAR WILL NOT START.
So you think it's petrol starvation and put in some more.
In this time the temp has gone down say if it took about an hour.
Now start the car - it starts - so you think it is the petrol problem.

BUT all the time it's been the CPS at certain temperature totally fails and at certain temp take longer to start! By the way CPS is NOT temperature sensor AS MANY PEOPLE on forums start thinking it is. It can be affected by temp but it actually send a signal for every turn of the engine (without going into too much technical details). There should be a certain resistance on a good CPS about 1K ohms.

If you had same problem as mine do what I have done!!!!

Anyone want help I've got access to Autodata to locate your CPS - I WANT TO HELP YOU ALL AND NOT SUFFER AS I DID...

Great forum!