Why does dV not display for Nerv engines in VAB?

[Poppa Wheelie]

I did a little research, and found a few people asking the same question, but I never saw an answer.  I've addressed some of the "try this" items I've found, specifically:

• Make sure the root part is not below the Nerv engines in the staging stack.  They are not.
• Make sure the dV calculating tool at lower right is set to vacuum.  It is.
• Turn the MechJeb dV calculator on.  It is.  Is also shows zero.
• KER info window in lower left also shows zero
• You can see plenty of fuel in the tanks

Is this just standard behavior, and I just need to work around it?  Or do I have an issue here?

Here's a much simpler craft, which I did in case other parts were somehow contributing to the issue.

[HebaruSan]

Looks pretty heavily modded. Wrong fuel/propellant, maybe?

[Superfluous J]

If you launch it and Alt-F12 it into orbit, does it fly?

i.e., did you confirm that it actually DOES have > 0 m/s of dV?

[Poppa Wheelie]

Yes, it flies.  Yes, it has the correct propellant.  See in the photo that it has Liquid Fuel.  Once in orbit, the correct dV numbers show up.

[king of nowhere]

I have many instances of nervs displaying deltaV correctly. sometimes the game gets it right, sometimes not. I never figured out how and why.

So I just do the calculation manually. Really, the rocket equation is not difficult to use. It takes a minute to check total mass, propellant mass, and calculate a deltaV. It's a lot faster and more reliable than trying to get the game to work properly.

[Poppa Wheelie]

5 hours ago, king of nowhere said:

So I just do the calculation manually.

Yes, this is what I've been doing.  It's inconvenient to have nothing in the VAB (or SPH) though.

[miklkit]

For me it is about staging with the NERVs in the 1st stage.