Re: 1980 300SD cold starting problem

Good news, I've solved the cold start problem and it's hard to believe
what it turned out to be.

I replaced the leaking fuel primer pump and then drove the car some
more. On this drive, I noticed that it seemed rougher at even warm
idle. Then later, when trying to accelerate from a stop, for a few
seconds after I pressed on the accelerator, there was no response.
This only happened once, so it was one of those things where you're
left asking yourself "Did that really just happen?".

After that I noticed that each time I stopped, at warm idle it was now
running rougher as well. Over the course of a 12 mile trip with some
stops at lights, it got so bad I had to put it in neutral or apply
throttle to keep it from stalling. Now I started thinking it's some
kind of fuel problem. On the way back, I took the highway and she
went easily to 85 and stayed there with no problems. Which I would
not expect if it were fuel, right?

I was planning on changing the 2 fuel filters as they were over due.
It's probably been 25K miles since they were changed. However,
given the symptom at the time was only a running rough at cold
starting problem, I would never have thought they could be the
culprit. I replaced the 2 filters as well as the short hose from the
metal fuel line to the fuel filter, which showed signs of cracking.
Started right up and ran perfectly smooth. Smoother than it's been
in quite some time. It past several start tests and driving around.
As a final test, I left it outside and got it down to 21F. Started
right up and idled fine.

So, I'm very happy that it's fixed, but really amazed at what it
was. Other than that brief failure to respond from a dead stop,
there was no indication of what I would expect a fuel problem to
exhibit. I would have thought I'd see problems on the highway at 85,
rather than at idle. But maybe it's because with a partially clogged
filter the fuel pump doesn't have enough power at idle to force fuel
through, but as speed picks up it does? Or I guess it could be
something in the filter that maybe came apart or wasn't made right to
begin with that somehow blocks flow at low pressure, but gets shoved
out of the way again as pressure increases? Or maybe that the fuel is
thicker at lower temps, so it cools off with the car, but then is OK
for warm starts?

Anyway, it shows the importance of the basics. I would have replaced
the filters right away or even months ago if I had one on those damn
metal washers that goes on the spin on type one. That's a major
annoyance. The filters don;'t come with the metal washer or the
rubber O ring for the bolt either. One would think they would
package them in. The oil filters always have several washers of
various types for the oil pan drain plugs, which aren't even part of
the filter housing. I've only found one online place that I think has
the metal washers. And a couple months ago, prior to this problem, I
ordered the washers at the dealer and they never called back to tell
me they were in.

And thanks to all here who offered help!
.

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