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Fuel Flow Monitor

FFM100 Overview

Maretron's FFM100 provides precision fuel flow information to help optimize fuel consumption, which can save thousands of dollars in fuel operating cost. The FFM100 uses state-of-the-art, positive displacement metering technology for unprecedented accuracy. In fact, the accuracy of the FFM100 is nearly that of commercial vessel systems costing tens of thousands of dollars, yet the FFM100 cost less than existing recreational systems found on the market today. Additional benefits of the positive displacement metering technology are the elimination of flow conditioning components such as straighteners and pulsation dampers. Other flow meter technologies require flow conditioning components that increase system and installation cost. The FFM100 also uses true temperature compensation with embedded temperature sensors within the meters. The returning fuel is generally hotter than the supply fuel and if not properly compensated, inaccuracies as much as 5% can occur in computing the engine's fuel consumption. The FFM100 also detects momentary reverse flow in the fuel lines due to fluctuating pressure caused by the injection pump. Less accurate systems count the reverse fuel flow as part of the consumed fuel where the FFM100 properly accounts for momentary reverse flow.

Lastly, the FFM100 can be used for fluid types other than fuel (e.g., water, oil, etc.) by ordering the appropriate flow sender.

The FFM100 is NMEA 2000® certified so you can view any and all information anywhere on the vessel using a compatible NMEA 2000® display. The FFM100 is a key component of Maretron's N2KView® vessel monitoring and control system.

FFM100 Features

  • FFM100 converts a variety of flow senders (e.g., fuel, water, etc.) to NMEA 2000® Network Data
  • All flow senders ordered separately depending on application (i.e., single fuel flow sender for gas engine, dual fuel flow senders for diesel engine, water flow sender for sea water, etc.)
  • Fuel flow senders facilitates fuel consumption optimization for reduced fuel operating cost
  • Fuel flow senders use positive displacement metering technology for superior accuracy over other measurement technology such as turbine meters
  • Fuel flow senders do not require costly fuel conditioning components like flow straighteners and pulse dampers
  • Fuel flow senders implement true temperature compensation with precision built-in thermistors for increased accuracy
  • Fuel flow senders automatically detect reverse flow due to fluctuating pressure difference from injection pumps
  • Fuel flow senders pass particle sizes up to 70 micrometers (diesel fuel filters normally filter down to 2 micrometers to prevent clogging injectors)

FFM100 Applications

  • Diesel Fuel Flow Monitoring
  • Gasoline/Petrol Fuel Flow Monitoring
  • Cooling Water Flow Monitoring

FFM100 Application Diagrams

FFM100 Accessories

Visit the Sensor Select Guide section for installation instructions and to determine the correct size and quantity needed. The following accessories are available for the FFM100:
Fuel Flow Sensor 0.033-1.67 LPM (0.0088-0.440 GPM) Part Number: M1AR Flow range : 2 to 100 LPH (0.53 to 26.4 GPH)

Fuel Flow Sensor 0.417-8.33 LPM (0.110-2.20 GPM) Part Number: M2AR Flow range : 25 to 500 LPH (6.60 to 132 GPH)

Fuel Flow Sensor 3-25 LPM (0.79-6.6 GPM) Part Number: M4AR Flow range : 180 to 1500 LPH (47.6 to 396 GPH)

Fuel Flow Sensor 8-70 LPM (2.11-18.5 GPM) Part Number: M8AR Flow range : 480 to 4200 LPH (127 to 1110 GPH)

Fuel Flow Sensor 10-100 LPM (2.64-26.4 GPM) Part Number: M16AR Flow range : 600 to 6000 LPH (158.5 to 1585 GPH)

FFM100 Sensor Select Guide

The following process exists as an aid for selecting the appropriate size fluid flow sensor(s) for your motored application. We highly encourage consulting with the Engine’s manufacturer for their recommendations before implementing any 3rd party solutions.

Maretron/Carling Technologies/Littelfuse will not be held responsible for any improper sensor selection or installation. Please consult with a local manufacturer and/or certified marine mechanic.

* If you are wanting to monitor a fluid other than a Fuel profile (Diesel, Gasoline/Petrol), please consult with our tech support team for guidance on the appropriate sensor line via email at

Terminology Reference Table

gph / GPHGallons per Hour
lph / LPHLiters per Hour
NPTNational Pipe Thread
Flow RateThe quantity of fluid that is passing through a cross-section of a pipe in a specific period of time.
Burn RateAlso known as Maximum Consumption, the quantity of fluid that is consumed for a period of time during a combustion process.

Sensor Table

Sensor SizeFlow Rate (gph)Flow Rate (lph)Port Inlet Size
M1AR0.53 – 26.42 – 100¼” NPT
M2AR6.60 – 13225 – 500¼” NPT
M4AR47.6 – 396180 – 1500½” NPT
M8AR127 – 1,110480 – 4,200¾” NPT
M16AR158.5 – 1,585600 – 6,0001” NPT

* Please take note of the inlet size of the sensor as an adapter may be required to interface into your fuel line setup. DO NOT choose a larger size sensor to mitigate fuel line adapters as this will hinder the accuracy of the readout or may not read at all. The flow sensors are rated according to the volume of fluid able to pass through the sensor and should not hinder the performance of the engine per principles of fluid dynamics.

For further technical reference about the Fuel Sensors behavior, please visit the FFM100 User Manual.

Step 1: Datasheet

Please locate the datasheet of your engine or generator. If you are unable to locate locally or online, please reach out to your local engine or generator manufacturer/dealer to obtain this information as it is crucial to identifying the appropriate sensors.

Step 2: Sensor Quantity

To determine the quantity of sensors per motor to apply, we must first review the engine setup.

Gasoline/Petrol-based Engines

In most cases, offers a single fuel line to the engine with no return to the tank, this requires only 1 sensor.

There are instances, mostly newer model years higher HP, that offers a gas engine setup paired with a return fuel line, we will require 2 sensors for this setup to detect the differential.
* For engines with a return fuel line, we will treat this installation and setup as we do for Diesel engine setups within Step 4 below.

Diesel-based Engines

In most cases, there will be both supply and return fuel lines within the engine setup to be monitored, therefore we will require 2 sensors for this setup.

There are very few instances, diesel engines less than 100HP may only have a supply sensor, no return, we will only require 1 sensor for this setup.
* For engines without a return fuel line, we will treat this installation and setup as we do for Gasoline/Petrol engine setups within Steps 3 and 4 below.

Step 3: Sensor Selection

Once we have obtained our engine’s datasheet and identified the quantity of sensors needed for your specific setup, we can now make our sensor selection.

Gasoline/Petrol-based Engines

For this type of setup where only a single sensor is being applied, review the engine’s datasheet to reveal the value Max Consumption or Max Burn Rate. This value illustrates the maximum fluid flow that would be pushed through the fuel lines while at full throttle.

You will use this value Max Consumption/Burn Rate as the same value as our max Flow Rate. Using the Sensor Table above, locate the smallest size sensor that supports your value. Sensors do cross supported range values.

Diesel-based Engines

For this type of setup where we have both supply and return lines, review the engine’s datasheet to reveal if the manufacturer has already provided these independent Flow Rate values. Unfortunately, most vendors haven’t populated this on datasheets, but it is always the best place to start. If the manufacturer does not provide this value, please locate the value Max Consumption or Max Burn Rate.

Once this Max value is identified, we will need to multiply by 2.5-3, marine industry average over the past 25-30 years, to approximate the maximum Flow Rates of the fuel lines. This estimates the maximum volume of fluid that is being pushed through the lines, whether or not it is used comes after this sensor.

Example: My engine’s data sheet reveals my Maximum Consumption at Wide Open Throttle (WOT) is 25 gph.

25 gph x (2.5 – 3) = Maximum Flow Range of 62.5 – 75 gph Flow Rate
(same conversion when using lph)

This would position this setup to use a set of M2AR Sensors.

*You will need to apply the same size sensor for both the supply and return lines for accuracy.

Step 4: Installation and Setup

The following Knowledgebase articles outline the path for each setup process as described.


We can understand and appreciate the concern with the sensor’s ¼” fuel line port on both the M1AR and M2AR sensors. As part of fluid dynamics, the Venturi Effect arises from the conservation of momentum and conservation of mass and relates the pressure along an enclosed flow (in a pipe) to the flow rate through the pipe.

This might seem counter-intuitive because the constricted region looks like it should be an obstacle (such as an inlet diameter reduction), so one would be tempted to think that the flow rate should decrease rather than increase. However, this would violate conservation of mass and conservation of momentum. Instead, to ensure the mass flow rate is conserved, meaning the continuity condition in the Navier-Stokes equation is satisfied, the flow rate must increase through this region.

This ensures that, once the constriction region is passed, the flow rate can be restored to its initial lower value and momentum is conserved throughout the flow region. Our applications rely on this principle to be able to predict a fluid’s reaction when flowing through constricted piping.

If you have any questions, please contact our support team at (866) 550-9100 or

Download Sensor Select Guide - PDF

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