RESPONSE TO QUESTIONS ABOUT ENGINE CHANGES AND I/M PROGRAMS

The Clean Air Act (Act) requires vehicle and engine manufacturers to certify that their vehicles will meet federal emission standards for the model year in which they were built, and they design and install the systems and components necessary to meet those standards. Federal emissions standards have applied to motor vehicles since 1968.

Section 203(a)(3) of the Act prohibits any person from permanently removing or rendering inoperative any device or element of design installed on or in any motor vehicle by the manufacturer for that vehicle to meet federal emission standards. Vehicles which have had emission control systems removed or modified can contribute up to five times the amount of pollution to the atmosphere as identical vehicles with the devices and systems properly installed. Accordingly, any change from the original certified configuration of a vehicle could be considered a violation of section 203(a)(3). This provision applies to all light-duty motor vehicles sold or offered for sale in the United States since 1968.

The attached Fact Sheet is intended to clarify our enforcement position concerning engine changes or "engine switching" (i.e., replacing engines with those that are not identical to the original engines). Basically, our enforcement policy is that EPA will not consider any engine change to be a violation of federal law if there is a reasonable basis for knowing that the emissions are not adversely affected.

Obviously, replacing a damaged or defective engine with an identical engine which maintains the certified configuration of the original vehicle is not illegal and, if properly done, will probably result in lower vehicle emissions. Since emissions standards have generally become progressively more stringent over the years, there is a presumption that vehicles built in the same or newer model year will be as "clean" or "cleaner" than older vehicles. Therefore, any other engine change would also be acceptable to EPA if the resulting vehicle is identical (with regard to all emissions related parts, engine calibrations, and engine and material vehicle design parameters) to any certified configuration for that general type of vehicle (light-duty passenger car or truck), so long as the certified configuration is for a comparable vehicle that is the same or newer model year as the original vehicle chassis. Therefore, if a vehicle is modified to be identical in all material respects to another certified configuration of the same model year or newer comparable vehicle by properly installing an entire powertrain and control system (including fuel system, evaporative system, transmission, ignition system, computer controls, exhaust system, and all the associated parts and accessories), we would not consider it to be tampering.

However, while it may be legally possible to insert a newer powertrain and control system from one vehicle manufacturer into an older vehicle or the chassis of another manufacturer, there is a concern that in practice these types of changes are usually not completed correctly either because of the prohibitive cost or the lack of proper ability or knowledge. As noted above, it is not a matter of merely replacing the engine. Therefore, EPA presumes this type of engine change to be illegal unless the person who installs the engine can demonstrate that he/she has or will correctly make all the necessary modifications to make the powertrain and control system in the vehicle identical to an appropriate certified configuration.

While replacing a worn out engine may result in lower vehicle emissions if it is properly done, the cost and complications involved in changing engines from one configuration to another may be impractical, infeasible or economically prohibitive in many situations. A person undertaking an engine change should be aware of the realistic costs and difficulties that may be involved. Our experience indicates that engine replacements often result in violations of the tampering prohibition, even where the engine is the "same" as the one originally installed on the vehicle.

The emissions testing that manufacturers perform to demonstrate compliance with federal standards is more comprehensive than the emissions tests used by the state and local Inspection/Maintenance (I/M) programs. For example, the federal procedures for light-duty cars and trucks require the vehicles to undergo prescribed sequences of fueling, parking, and operating in order to simulate an average trip in an urban area. Heavy-duty engine testing requires a similar transient mode testing procedure. During these procedures, the emissions are sampled continuously over the entire test cycle for subsequent analyses of specific components by prescribed analytical techniques. These procedures are more representative of in-use operation than any state or locally run emissions test.

The emissions measurement portion of the most I/M tests used by state I/M programs are designed merely as screening tests for identifying gross emitting vehicles which have not had proper maintenance (spark plug replacements, air filter changes, timing adjustments, carburetion adjustments, etc.), and not to measure compliance with federal standards or to detect whether specific emission control components are present and operational. The tests usually only involve the insertion of a probe into the tail-pipe of the vehicle while the vehicle is idling or operating at a constant speed and instantaneously measuring the exhaust emissions. A few state programs use a more advanced test procedure which is more sophisticated. However, these tests are not as stringent or accurate as the federal test procedures and the results are not comparable. It would be inaccurate to assume that just because a vehicle "passes" an I/M emissions test that it could also pass federal standards.

In order to help bridge the gap between the accuracy of the federal certification testing and the I/M emissions test, many state I/M programs also require that certain emissions related components be specifically checked for their presence and operation. In order to avoid the confusion created by the misperception that passing an I/M emissions test means the vehicle can meet federal standards, most I/M programs do not perform the emissions measurement portion of the test until the vehicle is properly equipped with the components that were originally on the vehicle as it was certified by the manufacturer. Some states have even attempted to reduce the problems associated with engine replacements and the emission systems by adopting stringent engine replacement requirements. Often this includes requiring the replacement engines to be identical to the original ones.

Since I/M programs are administered by state or local governments, any questions about administration of those programs and the legality of certain modification to vehicles should be addressed to the state or local agency in charge of the program.

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