Methods to Increase Fuel Efficiency in Post-Production Automobiles

This research examines potential improvements in post-production vehicle fuel efficiency, and establishes a set of equipment and protocol for further research into fuel-efficiency improvements. Fuel efficiency of post-production vehicles can be measurably improved by modifying the coding of the vehicle’s electronic control unit (ECU) to manipulate the air/fuel ratio and spark the engine’s ignition timing, resulting in increased fuel efficiency without a noticeable decrease in automobile performance. This low-cost modification, potentially applicable to most cars built in the 1980s and later, requires minimal investment by the vehicle operator, and fuel savings may offset that cost. A 1994 Honda Civic DX sedan was modified to include a Hondata s300 tuning system, allowing the ignition timing and air-fuel ratio to be modified, which is otherwise not possible on this and similar vehicles. This allowed modification of both the standard fuel and the standard spark ignition maps used by the vehicle, resulting in a reduction in fuel consumption per mile driven. Before modification, the vehicle was driven to establish its baseline fuel economy, an average of 34.0 MPG. The vehicle was then tuned to industry standard conditions, improving fuel economy marginally to 34.3 MPG. The vehicle was also tested for compliance with Oregon state emissions standards. Vehicle horsepower and torque were measured using a dynamometer in an auto tuning and repair shop to ascertain the impact to system output of the experimental trials in altering the tuning maps. Using the Hondata, the vehicle was tuned to have a leaner air-fuel mixture, and then driven under conditions similar to those driven under the base tune. Implementing this lean fuel map alone resulted in an improvement in fuel economy of 2.5 MPG to 36.9 MPG. Combining the lean fuel map with a spark map that advanced the ignition timing further increased the average fuel economy to 40.1 MPG, with a maximum obtained fuel economy of 52.6 MPG under near optimal highway driving conditions. Greater fuel economy improvements were seen in general under highway driving conditions than in stop-and-go or urban driving. In these trials, the vehicle’s performance was not noticeably affected. For example, this make and model of vehicle was shown under standard conditions to perform sub-optimally in climbing hills at high speed under standard conditions; the changes to the fuel and spark maps did not noticeably change this performance. The tuning of the spark and fuel maps resulted in a decrease in carbon dioxide emissions from the vehicle, but an increase in carbon monoxide emissions. The relative benefit or harm of this outcome is not assessed in this study. Though this study focused on a single vehicle, the results establish that improvements in fuel economy through changes to fuel and spark ignition maps are attainable without major modification to the vehicle or engine. This investigation also establishes a platform for additional study of modifications to vehicle operation which could further reduce fuel consumption without substantial reduction in performance. This low-cost approach to improve the efficiency of existing vehicles could be promoted by auto repair and tuning shops that could potentially profit from performing these modifications, or by government or public service entities interested in reducing fossil fuel consumption.

  • Record URL:
  • Summary URL:
  • Supplemental Notes:
    • This research was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
  • Corporate Authors:

    Oregon Institute of Technology

    27500 SW Parkway Avenue
    Wilsonville, OR  United States  97124

    National Institute for Transportation and Communities

    Portland State University
    P.O. Box 751
    Portland, OR  United States  97207

    Research and Innovative Technology Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Corsair, H J
  • Publication Date: 2015-3-10


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 42p

Subject/Index Terms

Filing Info

  • Accession Number: 01641592
  • Record Type: Publication
  • Report/Paper Numbers: NITC-SS-737
  • Created Date: Jul 24 2017 4:46PM