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Passing Smog 1987 Toyota MR2 4AGE Converted to 1988 4AGZE

I came into a stock supercharger for my MR2. It should bolt up with maybe a few extra parts right? Wrong! I bored out the cylinders and converted everything in and on my 4AGE engine block to a 4AGZE. Emissions wise it SHOULD be able to pass the smog test but a few key problems come to mind.

1. I got the car non-op'ed and never had the air box, so I have a cone filter on the air meter which is the first emissions device.

2. The A/C idle up vacuum lines are capped because I had to get rid of A/C.

3. After market muffler.

4. Added boost gauge and AFR gauge so there is an extra vacuum line and a second sensor in front of the catalytic converter.

So as I said, emission wise it should pass the smog test but I have heard conflicting things about those 4 points. Thanks for any info!


We're going to have to go straight to the book on this one Kobi. Considering the severity of the modifications you've made to the engine; boring the cylinders is probably one which we'll not be able to revert back from, there is a very high likelihood that your vehicle will not pass a California emissions test; and subsequently not be eligible for California public street use

1. The Cone Air Filter, so long as it has not required the tampering of any sensors or vacuum lines, will not cause a smog check failure.

2. The capped A/C idle vacuum line will cause a smog check failure (tamper).

3. The aftermarket muffler, so long as it has not required the relocation of the CAT or removal/relocation of an oxygen sensor, will not cause a smog check failure.

4. The addition the booster gauge and Air Fuel Ratio monitor will cause a smog check failure (tamper)

Should you drive in to your local smog check center today, the vehicle will fail the inspection due to the reasons mentioned above. Your alternative for a second and "more" official opinion is to visit a local smog check referee station. They will perform the smog check inspection as well are look over the entire "upgrade" job, and if all is well, issue your vehicle a BLUE TAG... meaning the vehicle has had an engine upgrade and passes the smog check. Subsequent emissions inspection can be conducted at regular smog check stations.

State Guidelines on Engine Rebuilds

When rebuilding an engine, it must be rebuilt to the original equipment specifications. However, if you decide to change an engine (install an engine not originally designed for your vehicle), the guidelines below must be observed to ensure that the vehicle will pass a smog inspection and subsequently be eligible for California registration.

Remember, these are guidelines for performing engine changes -- not certification procedures. All exhaust emission controlled vehicles with engine changes must be inspected by an official California smog check referee station and must have a Bureau of Automotive Repair (BAR) Vehicle Identification Label affixed to the doorpost (or chassis).

Remember also, state and federal anti-tampering laws generally prohibit any modification to the vehicle's original emission control system configuration as certified by the manufacturer. And, Section 3362.1 of the California Code of Regulations prohibits any engine change that degrades the effectiveness of a vehicle's emission control system.

California Engine Change Guidelines

- California Certification A federal Environmental Protection Agency (EPA) certified (federal or 49-state) engine cannot be used in a vehicle that was originally certified for California.

- Certification Standards.  Make sure the engine and emission control configuration on exhaust - controlled vehicles are certified to the year of the vehicle or newer, and to the same or a more stringent new vehicle certification standard.

- Classification.  Don't mix engine and vehicle classifications which will degrade the emissions certification standards. For example, a heavy-duty engine cannot be installed in a light-duty exhaust-controlled chassis even if they have the same displacement. Non-emissions controlled power plants such as industrial or off-road-use-only engines may not be placed in any exhaust-controlled vehicle.

- Computer Controls.  If a computer-controlled engine is installed in a non-computerized vehicle, the "CHECK ENGINE" light, the Original Equipment Manufacturer (OEM) diagnostic link, and all sensors, switches, and wiring harnesses needed to make the system fully functional must also be installed.

- Emission Control Configuration.  Mixing and matching emission control system components could cause problems and is generally not allowed. Engine and emission control systems must be in an engine-chassis configuration certified by the California Air Resources Board (ARB) or U.S. Environmental Protection Agency (EPA). The engine must meet or exceed the requirements for the year and class of vehicle in which it is installed.

- Emission Warranty.  Voiding the vehicle manufacturer's emission warranty is not allowed.

- Engine Modifications.  No internal or external engine modifications (cams, pistons, intakes, etc.) may be performed unless the parts are ARB-exempted or EPA-certified for use in the installed engine. Use the database on this site to search for aftermarket parts covered by ARB Executive Orders.

- Original Equipment.  The installed engine and host chassis must retain all of their original emission control equipment. Diesel-to-gasoline conversions must have all gasoline engine and chassis emission control systems installed (such as fill pipe restrictor, catalytic converter and evaporative emission system).

- Smog Inspection.  These vehicles must pass a complete smog inspection (visual, functional, and tailpipe).

This information is directly from the BAR. We posted this because of how stringent they are on engine changes. It is difficult for us to determine legal engine changes. Only a smog check referee can make the ultimate decision on whether or not a vehicle has had a legal engine change.

IMPORTANT NOTE: After the swap is complete, the vehicle will have to be inspected by a California State Referee. The Referee will ensure that the job was done properly and that the new engine does not pollute. If the vehicle pass the referee's smog inspection, the referee will issue you a BAR label which will be placed on your vehicles chassis and will be an indication that the vehicle is California emissions legal.

We highly recommend speaking directly with a State Smog Referee before beginning any work. You can contact the referee by calling (800) 622-7733.

posted by SmogTips Support

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