lpg how far out is the mpg reading on p38 if setup properly

[clj]

Just wondering if anyone has done a check to see how far out the figure is when running on gas, or how close it is.

[Gilbertd]

I assume you mean the mpg reading on the trip computer? If you do, then if the LPG system is set up correctly the mpg reading will be the same on gas as it is when on petrol. It's not correct and won't show what you are actually doing as it calculates fuel consumption from the length of the petrol injector pulses not by measuring how much fuel it is using. As the petrol injector pulses are still there, just not doing anything, it will continue to calculate how much petrol it thinks you are using.

If the LPG system isn't set up accurately or working properly, the petrol injector pulse length will be altered to correct for any variation in mixture so the computer will show a different mpg figure while running on gas. As mine is poverty spec ex-Plod, it doesn't have a trip computer.......

[clj]

Was convinced that was the case.

[clj]

Over a 380 mile trip, 70 mph fully loaded, trip computer said 20 mpg. My gas usage worked out to be 15.9 mpg.

Oh its definitely way out.

[Gilbertd]

But that's about 1mpg on gas better than I get. It's still the cost equivalent of 30 ish to the gallon though compared to doing the same run on petrol, depending on how much you pay for the gas obviously.

[mat_fenwick]

Do you know what the real petrol consumption normally is versus the trip computer? It's not unknown for the display to paint a better picture of the car's economy

[clj]

I have no idea if the mpg on petrol is true to the computers indication. Next challenge hey. But to do it accurately I should really fill it right up then just run it on petrol and fill, do the calc (expensive test).

Your on a single point are you not gilbertd and a 4.0, Looks to me like its running well then.

It was just motorway. Cruise control set so that the sat nav said 70. Which is just over what the Speedo says, and sometimes a little bit quicker if overtaking. The engine has just been rebuilt too, infact its only just done 3k since.

The gas is 77.9p liter at the mo. Was 80.9 when I travelled down to Cornwall. Gas has dropped in price and petrol has gone up, madness, think I might join the fuel protests outside work when they happen (hope I don't get the sack).