Liquid engine not working

[exxaminer]

Hey, I am trying to create a 2-stage rocket with boosters but the upper stage does not work.. I have liquid fuel and oxidizer, but engine status says zero delta v and when the stage is activated, nothing happens.. what is wrong?? 

 

Please help!

 

Screenshot: https://drive.google.com/open?id=13nDr6nYEebzWjP9jms5OwNIkLdv3I-jY

[Geonovast]

Welcome to the forum, @exxaminer

Any chance you have the two circled decouplers swapped in your staging?

[RoninFrog]

Are you enabling crossfeed on the decoupler?  If you are, turn it off.

[exxaminer]

thanks for advice - yes, crossfeed is disabled and decoupler staging double-checked.. i think i figured it out - it seems to be bug (or feature??): if you build the rocket from top to bottom (later stages are attached first), everything is fine.. but if you start from the bottom, upper stage seem to ignore fuel above it.. the same components only the build/placement order is different.. anyone had the same issue? this is second time this happened to me..

[Gargamel]

1 hour ago, exxaminer said:

if you build the rocket from top to bottom (later stages are attached first), everything is fine.. but if you start from the bottom,

I don't think I've ever tried to build a rocket from the bottom up, as you're describing.   I usually design my payload, whatever it might be, and then build the rest of the rocket below it.   Each stage you attach to the payload becomes the payload for the lower stage.  That way you can know how much rocket you need for the payload, not building a rocket and then limiting the payload. 

I do, however, build boosters specifically for certain payload ranges.   Ie, I'll build a series of rockets that can handle, lets say, 20-50, 50-80, and 80-120 ton ranged payloads to LKO.  I use large fuel tanks as the test payload to make sure they can get there.   Then I save them in the sub-assemblies category.    So when I build my payload, which might include transfer stages, I can know I can just drag and drop the premade booster of the appropriate size onto the vessel. 

[Geonovast]

Which part of the rocket is the root part might be tripping it up.  You can use the re-root tool to set the command pod as the root part and see if it makes a difference.