Experimenting with my 380SL ...

[cwmoser]

Been having some hesitation issues with my 1983 380SL.
Hesitates when cold.

My experiment is testing this and 3 days it seems to work - that is:
When the Engine is Cold turn the Ignition Switch to On, then Off
a couple times before starting. My supposition is that it builds up
Fuel Pressure. Doing this and I've noted that there is no hesitation.
Could be a fluke but so far the data is showing it to work.

[Diseasel300]

This is a coincidence, cycling the key is doing nothing to the fuel system. Unlike modern cars, these cars don't "prime" the fuel system when you switch the key. They have a pressure vessel to maintain fuel pressure, but the pump doesn't run unless the engine is actually rotating (early safety feature for the electric fuel pumps).

There are many things that can cause poor cold performance problems. Bad cap/rotor, warmup regulator issues, fuel pressure, cold-start injector problems, vacuum leaks, etc.

[cwmoser]

Originally Posted by Diseasel300

This is a coincidence, cycling the key is doing nothing to the fuel system. Unlike modern cars, these cars don't "prime" the fuel system when you switch the key. They have a pressure vessel to maintain fuel pressure, but the pump doesn't run unless the engine is actually rotating (early safety feature for the electric fuel pumps).

There are many things that can cause poor cold performance problems. Bad cap/rotor, warmup regulator issues, fuel pressure, cold-start injector problems, vacuum leaks, etc.

Perhaps you are right.
I need to collect more data to see if turning on the Ignition Switch momentarily
energizes the Fuel Pump. I had read somewhere that it did.

You mentioned several areas to look into - do you think the Accumulator
could be the culprit? My 380SL only has 45K miles on it and was tuned up
7 years ago at 41K miles. As you can see I don't drive it much and it
could have bad fuel or degraded fuel in the tank. I do though never do
a complete fill up to avoid gasoline being too old.

[Diseasel300]

These cars have a mechanical fuel injection system. The USA models had a feedback circuit for emissions and a catalytic converter, but that's pretty well where the differences end with the Euro models (some had a smog pump too).

Unless the engine is rolling, the fuel pump does not run. This is a trait common to the Bosch K-Jetronic system the engine uses and is a safety feature. Cycling the key in the ignition doesn't make the pump run. Newer cars, yes it does, these cars, no it doesn't.

Accumulator issues tend to affect starting performance. On my 500SL Euro, a bad accumulator would allow it to fire right up when cold, but sputter for a few seconds, then operate normally. Hot re-starts would usually be ok, but require slightly longer crank, but it simply would refuse to restart when warm due to vapor lock. You could crank until the battery died and that damn car wouldn't so much as fart! Let it cool back down and it was fine again. Changing the accumulator resolved these issues.

You mention that you don't fill the tank with fuel AND you don't drive it much. Bad idea. A partially full tank that's stored for long periods of time promotes condensation on the tank walls and collects water in the fuel. If you know you're going to be storing the car a lot, keep the tank full and use a fuel preservative like Sta-Bil when you fill up. I do this in the 500SL and never have problems (been doing it for over 10 years now).

I'd start with cap and rotor on the distributor, especially if old or hasn't been changed in many years. Pull the cap and check the condition inside. If it looks all burned, you see carbon, or the metal slugs are worn/ablated down, replace the cap and rotor and see if you have any improvement. When the engine is cold, humidity can cause misfiring through carbon contamination and also makes it more difficult for the spark to travel from the rotor to the plug. As the engine heats up, the spark is able to jump more efficiently AND the heat tends to dry out everything under the hood.

Following that, try to run the car out of fuel, then when you refill it, add a bottle of injector cleaner and drive that tank empty. If you have some questionable fuel in the system, that should help get rid of any varnish or gummy crap that's forming in there. It's also a cheap fix and one the car will benefit from anyway, whether it's the source of problems or not.

If you're storing the car a lot, keep the tank towards the full side and keep a fuel stabilizer in it. Sta-Bil says theirs will keep the fuel "fresh" for up to 1 year, though in my experience it'll keep it longer than that, even with our ethanol-poisoned fuel we have today.

If it's any consolation, you put more miles on your car than I have in the last 7 years. Mine does maybe 1000-1500 miles a year.