NG is not consistent, now my words might come out as total bull when seen in the better metered environment of this Volvo, but... Presently running in my classic via a single-point set-up, it could easlly be the vagaries of the open-loop system, but I think not.
My gauge tellls me the fuel varies slightly from day-to-day, one fill to the next. Not by much, but it's there.
Iveco, via Tesco's fleet have observed this;
The fact that biomethane is derived from material discarded by society makes it particularly environmentally-friendly. It is of course a close cousin to compressed natural gas (cng), but Iveco is apparently not all that keen on running vehicles on cng in Britain. Why?
The biomethane supplied by Gasrec is of a consistent, high quality. However, the natural gas that comes out of the gas pipe varies from one part of the country to another. OK, you can put in driers to make sure that it’s OK — ending up with water in vehicle fuel systems has been an historic problem with cng — but when it comes down to it biomethane makes a better story because of where it comes from.
https://www.whatvan.co.uk/analysis-and- ... 2010/iveco
I get the idea Gasrec - the Biogas supplier - is using this point to justify purchase from them; but the variance, from what I've seen is real.