With one ski, an odd noise in July is an odd noise. With eight boats at a rental base or a club, the same noise is a pattern you can only spot if every boat has been checked the same way. A short routine with a diagnostic dongle and a phone does that, with the same steps for every ski and the results written down per boat. The M-JET Diagnostic covers 37 Yamaha four-stroke models from 2002 on, the FX, VX, GP, EX and FZ series plus SuperJet and JetBlaster, and the app recognises each model itself, so a mixed fleet needs no setup per boat.
Before the season
Connect to each ski and read the fault memory first, before you clear anything, and write down what is stored. An entry from last September is information: it tells you what the ski struggled with at the end of its last season, and clearing it blind throws that away. Next read the battery voltage with the engine off and again while cranking. Weak batteries are a classic source of odd faults after a winter in storage, and a sag during cranking shows it before the ski ever reaches the water.
Then run the individual component tests. On a three-cylinder ski that is seven components, three coils, three injectors and the fuel pump. On a four-cylinder ski it is nine. The test shows that each part responds and makes a dead cylinder obvious in seconds. Keep in mind that the pump test shows only that the pump runs, not that it delivers enough. Fuel work calls for good ventilation and no ignition sources, and an engine is never run on land without a water supply.
Hours per boat, and where they sit
The hour meter on the dash isn't always reliable according to owners, and the control unit keeps its own count. The app reads total engine hours and the hours in six rpm bands up to 12000 rpm. The GP1300R has four bands up to 8000. For a fleet this is the useful part. Two boats with 300 hours can have lived very different lives, one mostly cruising and one with a lot of time in the top bands. Recording the figures at the start and the end of the season shows how hard each ski was ridden and which one deserves a closer look at impeller and wear ring. The scan can't see those wear parts. The hours only tell you where to look.
During the season
When a rider reports a beep or a loss of power, scan that boat before it goes back out. If the complaint only appears under load, record a test ride with rpm, temperatures, intake pressure and voltage, and compare the log with a healthy boat of the same model. That comparison is where a fleet has an advantage, because there is a sister ski to measure against. Where the model offers it, the app also resets the oil change interval and the maintenance or flush warning, so the display stops nagging about something already done.
After the season
Read the fault memory again before winter storage and compare it with the spring entry. A code that appeared and vanished three times over the summer deserves an hour in the workshop in October more than a breakdown in August. Hours per band go onto the same sheet. The app comes in variants for 1, 3, 5 or an unlimited number of vehicles, so a single dongle setup can serve the whole fleet, and the page on diagnostics for several vehicles gives the details.
What the routine won't do is find cavitation, a worn impeller, a stretched timing chain or lost compression. Those need hands and a trailer. There is more on the fleet side on the page about rental and fleet diagnostics. Keep the sheet simple: voltage, stored codes, component test result and hours, in the same order on every boat.
