Serious inconsistency with fuel tank vs usage

[v8vroom]

Hi all.

Car - 2000 Jaguar XJ8
System - Romano with Romano ECU.

I filled in 32L (7.03 gallons) of a 42L tank (The tank capacity is 50Lish. I struggle to fill above 35L)

I was able to drive 5.7 gallons (160 miles) before my car choked and could no longer continue on gas.
That's around 26L, almost 6L short.

Where do I even begin with troubleshooting?
I did mention this point on a previous post - viewtopic.php?t=19462

I will identify what tank I am running, 4 hole or single hole.

[Gilbertd]

Not sure I follow what you are asking. 160 miles on 5.7 gallons is 28mpg so what is the problem? Where does the 26L come from?

[v8vroom]

Not sure I follow what you are asking. 160 miles on 5.7 gallons is 28mpg so what is the problem? Where does the 26L come from?

My problem is I topped up 32L and I was only able to get 26L out of my drive (this is assuming the cars ECU is accurate for miles driven/petrol used)

[LPGC]

Or you got 32L out of your drive but your fuel computer isn't accurate.

We've recently discussed fuel computer accuracy (and what can effect it) on another thread.

26 versus 32 is around a 20% discrepancy. 20% Was mentioned on the other thread.

[Gilbertd]

My problem is I topped up 32L and I was only able to get 26L out of my drive (this is assuming the cars ECU is accurate for miles driven/petrol used)

It won't be as miles driven on LPG equals no petrol used. The trip computer is calculating how much petrol it thinks you have used not how much you actually use. As previously mentioned, the trip computer will never be right when on LPG. If the LPG system is calibrated correctly so the fuel trims do not alter between petrol and LPG, it will show an MPG figure when on LPG as when on petrol but you won't be doing that, you'll be doing less.