Sequence to start a M104
I have searched several archives and I cannot find what I'm looking for.
Having read everything I can on hard to start engines, here is my case and question:
1991 300CE (Euro) M104
Sometimes the care starts fine; occasionally it stalls on the first try, but starts on the second. It has done this most of it's three year life with me and from what Iíve read is not that uncommon.
In our second year, we developed a bit of a hum from the back seat. (Fuel Pumps), I opted not to change them right away.
Lately the car has become very difficult to start. Sometimes it may not start for 10 or more minutes or at least until some very specific things happen when I turn the key. My first response was to run down and buy a fuel pump and filter; yes, I only changed one. (I didn't realize there where two. Bad Chris, Bad Chris, read the forum...) Anyway the hum is gone but the starting issue is still there. Iím trying not to throw parts at it and try to isolate the exact problem or problems. Here is what I have noticed.
When I first turn the key, I can hear the fuel pumps run for a couple of seconds but there are two other noises. The first is very similar to the fuel pumps. Like a motor or actuator setting it self in place. If I don't hear this noise the result is always the same. The engine starts, stalls, and then will not start. If I cycle the key several times, the mysterious noise will appear and the car will start perfectly like nothing was wrong. I have not been able to isolate this noise.
The other one I notice is the fuel pumpís noise. Before the hum developed, they had a very smooth sound and stop. After I changed one, the sound is more like a smooth motor that runs for a second, stops then a tap more, stops, a tap more. I donít notice these additional taps (there are only three of four) when I hear the mysterious noise, perhaps because it is masked, but I canít rule out that they may be mutually exclusive.
One other important item, the car never stalls once it is running, if it starts, it is very reliable.
I have read several hundred posts on hard to start cars, but I still donít quite have the sequence of events leading up to a smooth start. Would someone mind going though the steps with me? Iím curious what sensors and relays come into play prior turning the motor over.
Sorry this is so long and I appreciate any help provided.