OK, am working through issues on this recently-acquired, somewhat neglected ol' girl...

With lots of misfires, have now replaced all plugs, isolated/replaced a bad coil and - importantly - have replaced both camshaft and crankshaft positions sensors.

Engine runs beautifully now; it's like a new car - except...

Still experience frequent hard starting. Typically takes 2 or 3 attempts at turning over, then always starts - and runs fine thereafter. No shuddering, misfires, power seems excellent. Hmmm...

Did I get a bad - brand new! - crank position sensor? Are findings consistent with same?

__________________
'83 300 SD
'05 E320 4Matic
'06 BMW 530 xi
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr

No I would look more toward fueling system.

How many miles are on it?

__________________
Jim

170k+ on the mileage...

Help me on the fuel deliver thought experiment... Important points are: Once running, car runs tremendously well. Absolutely no hesitation, and power production is robust, to say the least. Actually a very impresive engine, now that I feel it fully.

So by what mechanism would fuel be shut off (presumably?) while cranking, then turn on suddenly and fully after the third crank?

I mean, I was fully ready to blame injectors/fuel pump for my misfires, but these seem to not actually be in play. Or are they, in ways I don't understand?

__________________
'83 300 SD
'05 E320 4Matic
'06 BMW 530 xi
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr

See what the fuel pressure is on the fuel rail prior to the first start of the day before you try to start the car.

__________________
Jim

yeah, time to invest in the fuel pressure gauge...
Fuel pump was replaced only a couple of years ago; luckily have records for this car. Are these pumps known failure items?
Before I get the gauge on it, is a 'manual' test at the schraeder valve of any value?

__________________
'83 300 SD
'05 E320 4Matic
'06 BMW 530 xi
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr

X2 check fuel pressure. Could be an internal and or external (less likely) leak.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

It will at least tell you there is some fuel in it.

__________________
Jim

OK, before a couple of starts today - in all cases (today) started up immediately...

I've been turning key to 'Position 2' and waiting a few seconds before attempt to start. In all cases, depression of schraeder valve released some fuel under pressure - nothing shoots out after the first second.

Then car starts AOK. What does this tell us?

__________________
'83 300 SD
'05 E320 4Matic
'06 BMW 530 xi
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr

"Nothing shoots out after few seconds" sounds right. You are looking at residual pressure without the pump running. Sounds like system is holding pressure. When you checked it how long had it been since it had run?

__________________
Jim

RESOLUTION! - perhaps...

In case anybody is still reading this(?), a bit more data may be of use to someone...

Tested fuel pressure at schraeder with proper gauge - it's about 50 psi and the pump maintains this pressure. Further, with key off, pressure does not bleed down appreciably, so it doesn't feel like any kind of injector leak (though re-sealing the injectors is on the Project Plan.)

No, it's worse - 'cause I've wasted a lot of time on this. As part of general new-purchase maintenance, I replaced the camshaft and crankshaft position sensors. Stepping back through/testing everything, I put the old (Mercedes-branded, fwiw) camshaft position sensor back in, and the car has started reliably ever since. Replacement was a Hella (made in China) part. Draw your own conclusions.

Problem (perhaps) solved. Fingers crossed.
-----------------------
OK - still trying to diagnose...

Latest 'test': Car sitting for over a day; hadn't been started.

1) Attempt to start 'cold': Takes 2 'turnover' cycles to start. IE; position 2, engage starter, back to 0. Almost always starts on the 2nd try. 3rd at most.

2) Release of pressure at schraeder valve: yes; verified; some residual pressure in rail. Makes sense...

3) Holding key at position 2, definitely hear the whirring - I think? - of fuel pump, though hard to differentiate from SBC unit, which always seems to be pressurizing itself. Again, release of rail pressure produces a 'shot' of fuel.

However, car still starts immediately, even after release of rail pressure.
So, am I proving that I have a good fuel pump? Or that there may be some issue with pressure shutoff switch or sensor?

Again, car runs perfectly once running; no hesitations or evidence of fuel starvation under way. So it doesn't feel like an injector problem.

Thanks, Jim/others - Any experience/insights appreciated.

__________________
'83 300 SD
'05 E320 4Matic
'06 BMW 530 xi
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr