DIESEL FUEL METER

User Manual

Twin-sensor, temperature-compensated diesel consumption measurement — on your chartplotter, in your browser, and on the record.

1 · How it works

Diesel engines pump more fuel than they burn: the surplus returns to the tank, warmed by the engine. The meter measures supply and return with two positive-displacement flow sensors and computes:

burn = supply − return × (1 − 0.00083 × (T_return − T_supply))

The temperature term matters: with a typical 20 °C difference between lines, ignoring it under-reads consumption by roughly 3–10 % depending on your return flow — a bias no averaging can remove. Two temperature probes on the fuel lines correct it continuously.

The Fuel Meter is designed for mechanically-injected diesels — the classic sailboat engines that report nothing. Modern common-rail engines (Yanmar JH-CR, Volvo D2 EVC and similar) already transmit fuel rate from their own ECU and don't need it.

2 · Installation

Fuel system work. Install sensors in accessible, ventilated locations, use fuel-rated hose and clamps, check for leaks before and after the first engine run. If in doubt, have a professional plumb the sensors.

Plumbing

Supply sensor: between the primary filter and the engine's lift pump inlet, arrow in the flow direction.
Return sensor: in the return line to the tank, arrow toward the tank.
Temperature probes: strapped tightly to the metal fuel line right after each sensor, insulated with a wrap.
Bleed the system per your engine manual after installation.

Connections

The device connects to the NMEA 2000 backbone with a standard drop cable (bus-powered) and the sensor leads plug into the labelled terminals. An optional pulse output can drive an external totalizer (one pulse per configurable volume step).

3 · First start & WiFi

Power the bus. The counter starts its own WiFi network FuelMeter.
Connect and open http://fuel-meter.local (or 192.168.4.1).
WiFi tab → Scan → pick your boat network, enter the password, Add network, then Reconnect. The meter joins your network; the setup network returns whenever yours is unavailable.

4 · The web interface

Tab	What's there
Live	Burn / supply / return L/h, line temperatures, trip & lifetime litres, 30-minute consumption graph, trip reset, sensor warnings.
Economy	RPM, speed, engine load, litres per nautical mile, the datasheet-burn comparison, and the sweet-spot table (see §7).
Settings	Calibration K-factors, engine instance, smoothing, pulse output, and the engine-curve editor with graph, presets and sharing (see §6).
WiFi	Network scan, stored networks, reconnect.
Firmware	Over-the-air updates. Counting continues during the download.

5 · Calibration (do this once)

Each flow sensor has a K-factor — pulses per litre. The default is a nominal value; calibrate for real accuracy:

Run a measured volume of diesel through the supply sensor (hand pump into a 1 L measuring cylinder works well).
Compare the volume the Live tab counted against the real volume.
Corrected K = current K × (shown ÷ actual). Enter it under Settings and save.
Repeat for the return sensor.

Sensors vary a few percent unit-to-unit, and the burn figure is the difference of two large numbers — calibration is what turns good numbers into trustworthy ones.

6 · Engine curves

Two reference curves live in the device, editable as point tables (Settings tab, with a live graph):

Full-throttle line — the most fuel your engine can burn at each RPM. Used to compute engine load % (transmitted on the bus, shown on your plotter).
Expected burn line — the factory propeller-law curve: what a clean hull should burn at each RPM.

Ships preset for the Yanmar 3YM30AE; more presets download from the server (Refresh from server). The device also learns: sustained full-throttle bursts raise its max line, revving in neutral teaches the no-load line — the learned points appear as dots on the graph and survive restarts.

Calibrated a different engine? Share my configuration sends your tables to us for review — published presets become available to every device.

7 · Reading the Economy tab

With engine RPM (PGN 127488) and GPS speed (PGN 129026) on the bus:

L/nm — litres per nautical mile, live.
Sweet-spot table — every running second is filed into a 100-RPM bin; after some motoring the table shows the RPM band where the boat travels cheapest. Motor both directions to cancel current.
Datasheet burn — expected clean-hull consumption at the current RPM, with the live deviation. Consistently +15 % or more over the line usually means a fouled hull or prop.
Engine load — your burn as a percentage of the full-throttle line. At wide-open throttle a healthy, correctly-propped boat reads close to 100 %.

8 · On your chartplotter

The meter transmits standard engine PGNs — fuel rate and engine load (127489, twice a second) and trip fuel used (127497) — under a configurable engine instance (default 0). Raymarine, Garmin, B&G and Simrad displays show them in their standard engine pages with no setup.

9 · Pulse output

Settings → Pulse output: the output terminal emits one 50 ms pulse per N millilitres burned (your choice, e.g. 5 mL) for external totalizers or logging systems. 0 disables it.

10 · Troubleshooting

Symptom	Meaning / fix
"SUPPLY/RETURN sensor: no pulses"	One line flows while the other reads zero for 60 s — check the sensor connector and that the valve/line isn't blocked.
"temperature sensor invalid"	A probe reads outside −10…100 °C (disconnected/shorted). Counting continues uncompensated until fixed.
Economy tab shows "--"	No RPM or GPS on the bus — the engine gateway or GPS isn't transmitting PGN 127488 / 129026.
Burn reads 0 at idle	Normal briefly: burn is smoothed over the configured window (default 30 s).
Trip won't survive power-off	Totals save every 5 minutes while running and at engine stop — pulling power mid-run can lose the last minutes.

11 · Firmware updates

Firmware tab → Check for update → Apply. The download runs in the background — the meter keeps counting and transmitting — then the device reboots into the new version. Requires the boat WiFi to reach the internet.

12 · Support

Questions, calibration help, preset submissions: bad040@gmail.com