Measures: Exhaust Flow Rate


The SEMTECH® EFM4 is Sensors' 4th generation of proprietary rugged, compact Exhaust Flow Meters specifically designed for the measurement of total raw exhaust mass flow from either compression or spark ignition engines and vehicles.


Operating under the Bernoulli principle and laminar flow theory, EFM4 employs five high performance, dual-stage, differential pressure transducers which allow operation over an extremely wide dynamic range.

SEMTECH® EFM4 can be attached directly to SEMTECH® SCS or electrically and pneumatically connected via harness and heated line, respectively if the SEMTECH® LDV unit is installed inside the vehicle. Seven flow tube diameters: 1”, 1.5”, 2”, 2.5”, 3", 4", and 5”, are available to accommodate various engine sizes depending upon exhaust flow.

Available Tube Sizes and Flow Rates
SEMTECH EFM4 Tube Sizes and Flow Rates Chart

The SEMTECH® EFM4 is the first generation of EFM where all measurement components are completely self-contained in a single module mounted directly on the flow tube, eliminating the need for transport lines, and continues to offer the following benefits:

  • High Speed Sampling: The EFM4 internally samples the differential pressure channels at up to 5 kHz, accounting for every pressure pulse from an engine, from idle to maximum rpm. Standard output rate is 1 Hz.
  • Back Purge: A software-controlled back purge pump is included in the heated sampling flow tube assembly, along with solenoids that route high pressure air backward through the Pitot tube, purging contaminants and any condensation in the pressure lines. No dismantling is required.
  • Autozero: With a single software command, internal solenoids open the pressure sensors to ambient air, allowing fast and easy zeroing while the engine is still operating.
  • Sampling tube assemblies come with two elbow extensions to facilitate installations.

EFM4 Diagrams

Each heated tube assembly includes the following accessory kit (unique to each size):

  • Marmon Flange Clamps (2)
  • 90° Flow Tube Extension Inlet (1)
  • 90° Flow Tube Extension Outlet (1)
  • Gaskets (2)
  • Extension Cable (POE)
  • Hard Case for Flow Tube and Harness
  • Pneumatic Capacitor (for 1.0”,1.25”, 1.5”, 2.0” gasoline vehicles only)