I finally measured my fuel pressure on my 300CE91 - 104.980, to try to see if I get some bleeding causing me this bad start when the car has been seated for more than 30 minutes (basically when I start it on the morning at about 50F, it's kind of fine, if I have to re-start after 30 min it was turned off, even if it was run for 10 seconds - so not having time to be warmed - it will start an die right away and then restart OK).

What I did is attaching the pressure gauge to the top part of the fuel distributor, this is what I got:

- engine runing and cold (60 F outside):

P = 6.35 bars (92 PSI),

- engine off (immediately after the previous test, so engine was not really warmed up, just ON for 2 minutes):

Engine off P = 3.35 bars (48.6 PSI),
After 12 min P = 3.2 bars (46.4 PSI),
After 40 min P = 3.1 bars (45 PSI),
After 80 min P = 3.0 bars (43.5 PSI),
After 2 hrs P = 2.9 bars (42 PSI),
After 17 hrs P = 2.6 bars (37.7 PSI).

Can we talk about bleeding? I don't find these drops to be big.
Is that eliminating bleeding in my bad start issue?
What do you think?

Also I wanted to mentioned that I was surprised to ear, that when I released the fuel pressure at the fuel distributor by untighting the top M8 - 1 mm screw, a kind of whistling/air bleeding noise coming from the area where the fuel pumps are: is it normal? Is it just the fuel accumulator noise when the pressure is released?
I tested a few weeks ago by pulling some vaccum through the air side of its membrane: no fuel came out so I conclude it was good, correct?

Fuel pressure regulator is new, injectors also (except cold start one).

Any ideas?

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From 300CE to SLK230K