EPA E-mail
I e-mailed the EPA about the matter about a week ago and they just got back to me. I havent really looked at it all yet but I figured I would post it.
Thank you for your inquiry to the EPA Web site. Your request has been received by the Headquarters Public Access Service, a contractor operated reference and referral service.
You asked if it is legal to convert your gasoline engine to a diesel engine.
The Public Access Service is a library reference and referral service and cannot provide regulatory guidance or applicability determinations. We are providing the information and referrals/contacts listed below so that you can seek that support directly from Agency program staff or other information services that can provide that assistance.
We suggest you contact the Office of Transportation and Air Quality (OTAQ) directly. Contact information for OTAQ is online at
http://epa.gov/otaq/oms-cmt.htm
You can find OTAQ contacts listed by topic here:
http://www.epa.gov/otaq/oms-cont.htm
Because you indicated that you would be switching engines in order to convert a gasoline powered vehicle to a diesel one, please see the fact sheet on Engine Switching from the Office of Compliance.
Engine Switching Fact Sheet:
"For light-duty vehicles, installation of a light-duty engine into a different light-duty vehicle by any person would be considered tampering unless the resulting vehicle is identical (with regard to all emission related parts, engine design parameters, and engine calibrations) to a certified configuration of the same or newer model year as the vehicle chassis, or if there is a reasonable basis for knowing that emissions are not adversely affected as described in Memo 1A. The appropriate source for technical information regarding the certified configuration of a vehicle of a particular model year is the vehicle manufacturer...
Many states also have statutes or regulations prohibiting tampering in general. Most of these laws specifically prohibit tampering by individuals. A few specifically prohibit engine switching, using provisions similar to those stated in EPA's policy."
http://www.epa.gov/compliance/resources/policies/civil/caa/mobile/engswitch.pdf (PDF, 3 pp).
You may also be interested in the Office of Transportation and Air Quality (OTAQ) web page on alternative fuels and converting vehicles to alternative fuels (sometimes called "aftermarket conversion").
Alternative Fuels
http://www.epa.gov/otaq/consumer/fuels/altfuels/altfuels.htm
For information on fuel economy, including tips to improve gas mileage, please see:
Fuel Economy > What You Can Do
http://www.epa.gov/fueleconomy/whatyoucando.htm
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