Yamaha Outboard Live Engine Data on Your Phone

An F115 that suddenly pulls back the rpm half an hour into a run won't tell you why. The answer is often in the values the ECU is measuring at that exact moment. With M-JET DIAGNOSTIC you see that live data on your phone while the engine runs, at the dock or out on the water.

What you can see

• Engine speed, ignition timing and injection duration
• Intake air pressure, atmospheric pressure and intake air temperature
• Cooling water temperature or engine temperature, on some engines also water pressure and the thermo switch
• Oil pressure in kPa or psi on many engines from the F115 class up
• Battery voltage, on big engines also the accessory battery voltage
• Throttle valve angle and TPS voltage, with electronic throttle and shift also the APS lever sensors and SPS shift sensors
• Fuel flow in gal/h, speed and trim level in percent
• Switch states such as engine shut-off, shift position, main relay and fuel pump relay

Anywhere from 14 to 65 values, depending on the ECU

How many values you get comes down to the ECU. An engine in the F20 to F100 class gives you 18 to 30, a V8 in the F275 to F450 class up to 65. The HPDI Z series two-strokes show 34 values, including fuel pressure in MPa, O2 sensor voltage, the firing state of each cylinder and the oil level switches. Engines with variable cam timing show the intake cam angle, V engines separately for each bank. Temperatures, pressures and speed are available in US and metric units.

How to read the numbers

A single number tells you little, the trend tells you a lot. If engine temperature climbs under load while water pressure drops, look at the water intake screen and the impeller first. If the temperature stays low all the time, a thermostat stuck open could be behind it. If battery voltage sags hard while cranking, it's more likely the battery or a cable than the starter. On engines with variable cam timing, the intake cam angle should read 10 degrees or less at idle in neutral. A clearly higher number points you to the OCV and its filter screen. TPS voltage should climb smoothly as you slowly open the throttle, with no jumps. And fuel flow helps you compare against earlier runs: if the engine suddenly burns a lot more at the same rpm and load, something is off with the engine, the prop or the hull.

What live data can't show you

Live data is sensor data. The ECU has no idea what the impeller looks like, whether there's water in the lower unit or whether compression is healthy. A tired impeller shows up indirectly at best, through water pressure, and only on engines that measure it. For readings underway, bring a second person so one drives and one watches the phone.

Related topics

• Yamaha Outboard Overheating: Check Cooling Water Pressure, Temperature and Thermo Switch
• Yamaha Outboard Oil Pressure Warning: Sensor, Wiring or Real Pressure Loss
• Yamaha Outboard Limp Mode: Tracking Down Power Loss and RPM Limiting
• All Yamaha outboard diagnostics topics

Everything runs via app over Bluetooth, for Yamaha outboards with control unit generations from 2003. Learn more about the M-JET DIAGNOSTIC for Yamaha WaveRunner & Outboard.