Measuring Fuel Economy

One of the least accurate measures of fuel economy is the engine ECM data, according to Tim Tindall, director of component sales at Detroit Diesel.

In a detailed presentation during the Freightliner press days in Napa Valley last week, Tindall showed how his company runs fuel economy tests to verify its claim of industry-leading fuel economy. He said the convenience of the ECM fuel reports is far outweighed by the fact that many times the reports are not measures of fuel consumed but mere calculations. Not only do they not measure fuel used, he said, but often the manufacturer may set the software to “aggressively” report fuel consumption.

Read what you will into that, basically it means the truck will report it’s getting a certain mpg, but it’s actually an optimistic number. “But because it’s electronically reported, people believe it’s the truth,” said Tindall. This can create significant concerns with truck fleet managers who compare ECM reports from brand A with brand B.

Detroit Diesel has gone to great lengths to ensure its ECM reports are within 1% of real fuel consumption. If the other brand is reporting wildly optimistic consumption, Detroit Diesel will do some in-fleet testing to show the discrepancies and prove that the Detroit Diesel economy is always at least 5% better than the competition.

In carefully controlled testing, Tindall said Detroit Diesel goes to extraordinary lengths to match up the specs of competing trucks. In the real fleet world, that may not be the case, but these verification tests are as close to Detroit Diesel protocols as possible and the numbers are directly comparable ‒ unlike ECM reports.

The testing at Detroit Diesel is a combination of track time and on-highway SAE/TMC Type III and Type IV economy tests. The distances are great, the conditions are precise, the repeatability is excellent and the data analysis is meticulous.

This all takes time, he said, but whenever there’s a customer complaint that the Cascadias are doing less well than a competitor, a “flying squad” of Detroit people go to the fleet, run as much testing as it takes and, in every case, prove the Cascadia is, in fact, the fuel economy champion. So sure are they of this that the Detroit Diesel and Freightliner managers at the meeting put their hands on their hearts and said that under the controlled testing conditions, it always comes out 5% or better in favor of the Freightliner/DDC combo.

In discussions over lunch, I asked Brian Cato, who had made a presentation about the Virtual Technician product, about the reports that are available on the engine ECM that are reported back as part of data collection. Included are real-time fuel consumption and load factor, and Tindall had said there is a straight line relationship that allows for comparisons of different trucks, even when they are running at different load factors. The long and short of that is you can watch out for Virtual Technician to move from the reactive responding to a problem on the highway to becoming much more proactive.

A case in point is being able to look at a number of trucks in a fleet at the same time and see those that are doing less well on fuel. Then they can make the call: “We can see a couple of your trucks are using more fuel than the norm.”

This represents something new: the ability to spot problems developing with a power unit, problem drivers who are not working to get the best fuel economy, or maybe even fuel theft.

All of which any manager would like to know and fix.