Having had some time to go over our experiences of the last week or so it seems that yet more “tweaks” will need to be made to the fuel system although, thankfully, nothing too painful.

The good news was that with the 90 fully loaded in “overland” mode the new MAF sensor I fitted just before we left has brought the fuel consumption back into the realms of “reasonable”. With a mix of motorway, dual carriageway, narrow B roads and some town driving we were getting just above 24MPG during the trip. Having the twin tanks really let us push the limits on range without having to worry about running out of fuel. The main tank gave us a range of just over 430 miles without running out – I’d have let it run out just to see how far we could have got on it but we were on the motorway at the time and I didn’t fancy having the engine stop in that environment. We haven’t taken the front tank more than 200 miles yet but it’s looking as if the combined range is going to be in the region of 750 miles.

The only problem we’ve encountered is that the fuel gauge isn’t directly connected to the sender on the TD5, instead it’s controlled by the Speedo… really, it is ! The speedo prevents large changes in the gauge reading which probably serves to stabilise it off road. The problem is that when you change tanks, if the fuel levels are very different, the gauge takes 30 mins to adjust unless you turn the ignition off and back on again.

As a result I’ve been pondering on a way to resolve this and also to give a more believable fuel gauge reading for the current selected tank. The battery/fuel monitor will now drive the dashboard fuel gauge directly, bypassing the normal speedo circuit. The monitor will be connected directly to the two fuel tank senders and I can then calibrate the sender for each tank in the firmware. It will also light up the dashboard “low fuel” warning light (another job the speedo does at the moment). I got the gauge driver hardware/software working today, I just need to change the display to a smaller 2 rows x 8 characters display to make it easier to mount it somewhere in the dash.