PIT report finds ECM-generated fuel consumption data not precise

by Truck News

MONTREAL, Que. — Relying on fuel efficiency data provided by the engine electronic control module (ECM) may not be good enough when making decisions regarding fuel economy, a new technical report from PIT Group has revealed.

The report examined fuel consumption data from the ECM on several vehicles then compared it to actual fuel consumed. Significant variances were discovered.

“The ability to measure fuel consumption accurately and precisely and defend the results is critical for writing vehicle specifications, for establishing effective maintenance practices, and for training drivers to operate vehicles as fuel efficiently as possible,” said Yves Provencher, director of PIT Group. “Our tests show that engine ECMs present different levels of precision and accuracy, and that ECM data should be used with caution for evaluating the impact of a fuel saving technology or operational practice.”

The study was conducted in the fall of 2014 using 14 different vehicles with engines from four manufacturers. Actual fuel consumed was measured using the Joint TMC/SAE Fuel Consumption Test Procedure Type II protocol. Key findings included:

• Cummins (four vehicles were tested for a total of 24 tests): accuracy from -5.4% to -6.2%, precision from 0.18 to 0.81%;

• Detroit Diesel (seven vehicles were tested for a total of 27 tests): accuracy from -2.6 % to 2.1%, precision from 0.37 to 1.09

• Mercedes (one vehicle was tested, nine tests were conducted): accuracy of -0.9%, precision of 1.59%

• Volvo (two vehicles were tested for a total of 29 tests): accuracy of -3% and 0.9%, precision of 0.25% and 0.84%.

For all engines except the Mercedes, the ECM indicated lower fuel consumption than the gravimetric measurement, PIT found.

You can read the full report here.


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  • There are many, many factors that affect the accuracy of the ECM fuel efficiency data and it requires constant attention and adjustment to the OEM’s calibrations to maintain this accuracy. Its a moving target. So to state the numbers that you have in this article without clarifying which engine models were tested and which ECM calibrations were used in the tests renders this information as meaningless other than to say that its not perfect. Also, you stated that you used the SAE Type II test procedure so I will assume that the test was conducted on a closed course as opposed to an open road which does not provide for real world data due to the fact that the engine is operated at constant speeds and loads. In other words, your data totally ignores the transient loads that an engine is subjected to in real world driving conditions and those transients also have a great effect on the ECM accuracy. The Type IV test procedure conducted on open roads would have been the preferred method to conduct this test along with an analysis of utilizing fuel economy data from fleets using each of the engines.

  • Why use an algorithm
    ECM measures actual fuel used
    Odometer measures actual miles traveled
    division is simple
    Instantaneous use algorithm
    average = division
    algorithm is self correcting because it looks at average to make adjustments