Cannot solve oxidizer-starved engine

[athalon020]

Hey everyone,

I built the Saturn V in my sandbox save for grins and have flown it a few times without the Lunar Module with everything working perfectly.  However, ever since I added the Lunar Module, the engine for the Service Module has stopped working and I cannot figure out why.   To begin, here's an image of the craft as it is, and below that is a breakdown of the parts that aren't working correctly:

 

Parts list (top down):
- MK1-3 Pod
- TD-25 Decoupler
- SM-25 Service Module (Following four parts are within the SM)
---FL-T200 Fuel Tank
---FL-T400 Fuel Tank (Both tanks are in the center)
---Stratus-V Monopropellant Tank (4x around the center tanks)
---RV-105 Thruster Block (4x on the outside of the Service Module)
-RE-J10 Wolfhound Engine ***This is the offending engine***
~~~Below are the Lunar Module Parts~~~
-Clamp-o-Tron Junior
-Munar Excursion Module
-48-7S Spark Engine
-TD-06 Decoupler
-FL-TX220 Fuel Tank
-48-7S Spark Engine

The issue comes whenever the Pod and Service Module are disconnected from the rocket. I can imagine I'm doing this improperly (but it's the only way I've figured out how to do it), but I'll deploy the shroud, then I have to decouple the Clamp-o-Tron Jr. which frees up the two craft.  At this point, I can start the Wolfhound which immediately says "Oxidizer Deprived" and will not run.  The tanks inside the service module are both full at this point, so the rest of the rocket isn't draining the fuel from these tanks for whatever reason, it just isn't giving fuel to this engine.

I've tested the rocket on the launch pad by fixing support structures to the top and going through the entire sequence and it always results in the Wolfhoud being starved of oxidizer in this configuration.  However, if I run the exact same test without the Lunar Module on the rocket, the engine works just fine and will pull fuel from the tanks inside the Service Module.  Also, if I build the two craft in a new build, the engine works by going through the same steps as with the full rocket.

So with all that known, is my rocket bugged and I need to just rebuild it?  Or have I got a combination of parts that are preventing this engine from working?  I've been trying to work this out for a few days and I'm just at a loss now...

Thank you!!

[Foxster]

It might be saying starved of oxidizer but it might be starved of LF too. 

You have your fuel tanks clipped inside the service module (after being surface mounted?) and so it's not obvious just how the fuel flow will be working from those tanks to the engine. You could try adding some fuel ducts from the tanks to the service bay or the engine and see what happens. 

[Espatie]

Turn on the fuel flow diagram and screenshot that for us.

[Daveroski]

When you took all the fuel out to check it's COM fro the RCS did you remember to put it back?

D.

 

 

[HvP]

Right click on the tanks inside the service module and look for a little green triangle beside the fuel bars. If you see a red circle crossed through in that box then that means the tank has been locked and the fuel won't flow.

Edited January 18, 2019 by HvP

[athalon020]

 

20 hours ago, Espatie said:

Turn on the fuel flow diagram and screenshot that for us.

This actually seems to be the problem!  I was unaware this was a feature but here it is (arrows are pointing upwards):

 

Foxster's suggestion of a fuel pipe to the base of the Service Module has solved the issue!

Edited January 18, 2019 by athalon020

[Espatie]

By the looks of it Fuel Crossover is disabled for the Service Bay.

[HvP]

@athalon020 Is it possible that when you placed the tanks into the service bay you actually surface attached them to the side of the TD-25 decoupler above it before sliding them into the service bay?

Decouplers don't allow fuel to flow across them by default and if you stuck the tanks to the side of that decoupler the game might be reading them as being on the other side of the decoupler and blocking the fuel flow. Try removing the tanks and attach them to the sides of the lower part of the service bay instead and then use the slider tool to move them into position.

Or even better, if you hold down the ALT key while placing the tanks it should make it a lot easier to stick them to the green node positions inside the service bay.

Edited January 18, 2019 by HvP

[bewing]

There is a known bug in version 1.6.1 with fuel flow in the SM-25 module. Yes, fuel ducts are the best workaround for now, if the bug bites you.