"The (Gill Sensors) device has obvious fluctuations," Red Bull's Dr Helmut Marko has now told Austrian television Servus TV.
"It does not give precise measurements, when in our opinion we were within the (100 kilogram per hour flow) rules," he insisted.
But Gill, a British company, said in the wake of the Melbourne controversy that it has the backing of its client, F1's governing body.
It said the FIA "provided Gill Sensors with positive feedback on the performance of the fuel flow meter (in Australia), confirming their confidence in the development and stating the meters meet the FIA's accuracy specification."
Red Bull is expected to follow through with an appeal against the Ricciardo ruling, but the fuel flow saga may only be a blip as the champions continue their chase of dominant 2014 team Mercedes.
"The speed with which Red Bull has caught up should make everyone worry," Williams' Pat Symonds is quoted by Germany's Auto Motor und Sport.
Red Bull boss Christian Horner confirmed that the team and its struggling engine supplier are making clear progress.
"At the Bahrain test the Renault was at 10 per cent of what it can do," he said. "In Melbourne we were at 60."
Renault chief Rob White, however, warned: "We are not out of the woods yet. In our steep learning curve, further setbacks are inevitable."
But the huge progress since Bahrain means car designer Adrian Newey can now get down to the real challenge of 2014.
"I have only now begun with the development of the car," he said. "If you can't drive, you can't try anything."