Charging Problem

Try inserting the plug into the wall again. It should be quite stiff and the plug should be fully inserted and flat against the receptacle.
Remove and replace the adapter (not while it's plugged in--I know you know this)
And finally make sure the car end of the UMC has a good connection. I find it helpful to insert the plug somewhat slowly so that you hear two distinct clicks.

jerry33 said:

Try inserting the plug into the wall again. It should be quite stiff and the plug should be fully inserted and flat against the receptacle.
Remove and replace the adapter (not while it's plugged in--I know you know this)
And finally make sure the car end of the UMC has a good connection. I find it helpful to insert the plug somewhat slowly so that you hear two distinct clicks.

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Good advice and I bet it works.

It's either a bad master charger, or UMC. If you have a 40A+ j1772 or HPWC nearby, you could find out which it is.

"30 amps is better than 16..." Says the Volt owner with a Jesla

smsprague said:

Found a 70 amp charge point station in town - I have single charger in my Tesla. It charged at 40 amps. So I am guessing UMC issue.

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I thought each charger was limited to 40 Amps? What you saw sounds right to me with a single charger. Unless it's a DC charger, but that is currently limited to CHAdeMO or Superchargers, as far as I understand.

NO! Level 2 charging is limited to 80 amps. The wimpy 30-40 amps is what the government mandated!

smsprague said:

Found a 70 amp charge point station in town - I have single charger in my Tesla. It charged at 40 amps. So I am guessing UMC issue.

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Or adapter, or outlet, or outlet wiring (OK, the wiring probably didn't go bad if it's worked since you got the car). You changed a bunch of variables all at once - all you can definitively say is everything inside the car can charge at 40A.

Can you find another 14-50 to plug into and test? Problem goes away, I'd blame your outlet/wiring. Problem continues, you have an issue with the UMC or adapter (but that doesn't necessarily rule out your outlet/wiring). Also try another owner's UMC/adapter on your car and outlet if you can.

Is your outlet/adapter getting hot (more so than before)?

Heat at your outlet is not important. Find another source to plug your 14-50 adapter into. If the problem continues it is the UMC. If it does not, then it is your wiring.

I went on plugshare and filtered out all but 14-50's in Tucson. There are a few listed you could try (although some seem to be 6-50's, so you couldn't use your adapter on those).

Do you know how fast the charge rate drops from 40A? If you reset it to 40A, does it drop right away? What is the reported line voltage while charging at 40A and 30A. Also try dialing the charge rate all the way down and see what the voltage is.

Are there other heavy loads kicking in during charging (I'm thinking A/C compressor, especially if this is happening during the day)?

smsprague said:

Charge rate drops to 30A within 10 seconds even on a scheduled charge. My voltage is 240V - it's stays consistent. I am using a 6-50 adapter.

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"Andy M" and "Rush" have 6-50's listed on plugshare in Tucson. I'd try to head over there for a quick test. If they have a UMC you can test on their outlet as well, that would help isolate the problem. If they have a 6-50 adapter you can test with your UMC, that would narrow it down further (their UMC/your adapter and your UMC/their adapter).

smsprague said:

Nothing else is using power this is a new garage with its own 100A panel.

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If the garage panel is a subpanel off the house, it will still be impacted by a big load in the house - ie, an A/C compressor kicking on would cause the same voltage drop at the garage outlet, regardless of whether the outlet is wired directly to the main panel, or there is a sub panel between the two.

If the garage has a dedicated service entrance with its own meter and connection to the transformer, that's a different story.

But if the voltage isn't sagging when the current ramps up, this probably isn't the issue.