fuel vacuum issues on KX0404

[stoneCold.]

just bought a 2020 Kubota KX040-4 was sucking air and dying at high idle. I fixed a leaky water separator bowl, but now I’m seeing weird constant vacuum on the system. like -10 to -20 psi at full throttle

I’ve replaced the filters, swapped the pump, added a second inline pump, and even cleaned the tank, no change
the only way I can get the pressure to rise is by pinching the injector return lines, but then it just throws a fuel pressure code.
It feels like it’s bypassing too much fuel back to the tank instead of holding pressure
has anyone dealt with this? am I missing a relief valve or something in the return circuit?

 

[Orangebuffalo]

Ran into a vacuum headache with my Kubota once. I swapped out pumps, but it wasn't until I noticed an injector line clamp was misaligned that things got back to normal.

 

[Axon]

Did some digging, hope this helps.

Constant vacuum and low pressure despite new pump/filters suggests restricted fuel supply line or partially collapsed pickup tube in tank. -10 to -20 psi vacuum is excessive should be closer to 0.

Check:

- Fuel tank vent (clogged vent creates vacuum)
- Pickup tube/sock in tank (collapsed or restricted)
- Supply line from tank (kinked or internally collapsed)

Pinching return lines raises pressure because you're forcing fuel forward instead of back to tank—that's masking the real issue, which is insufficient supply flow.

Pull the tank pickup assembly and inspect for blockage or damage. That's the most likely culprit.