HPDI Excessive fuel consumption

Newby here , I found this site thru web search , Using local search, I was impressed by the technical knowledge of it's members. Great site........
I'm actually posting for a bud who purchased an older Edgewater 20cc with a 200 HPDI. His fuel consumption has been twice what was expected, managing only 2 mpg at cruise. A boattest site had him expecting 4 mpg at 25 mph.
Compression tested fine prior to purchase, prop is original and the engine runs fine. Can anybody offer any insight before he starts spending at the Yamaha dealer ?

Especially when you are talking about a direct injected engine you really need to get it hooked to a diagnostic computer to see what's going on.

The engine computer uses the input from multiple sensors (which read everything from air and water temperature to manifold pressure) to determine "how much fuel" to send to the cylinders.

Even a minor sensor failure, or a vaccum leak can result in them "drinking" gas.

Your buddy should have made "a satisfactory tech check" a condition of sale - some of the electronic components on these can be quite pricey.

So, assuming that the hull has not soaked up a few hundred pounds of water due to cracks or breaches in gel coat, the motor was correctly propped in the first place, there are no "cooties" on the hull causing excess drag and the boat wasn't overloaded or anything else except for the engine itself to explain the poor fuel economy, it's time to "plug it in" and see whats going on...

And yes, real life tests from boattest.com does show that this combination is capable of getting 4 mpg at about 25 mph with 2 persons on board, 1/4 tank of fuel, minimal gear and no water in the wells running a 15 1/4D 19P stainless prop in relatively calm water...