Since California's passing of a new diesel emissions law for vehicles with less than 14,000-pound gross vehicle weight ratings, we decided to take a closer look at the test and all it entails. What we found was the majority of slightly modified '98 to '07 trucks have no major obstacle to overcome in order to pass a smog test. The key to passing will be to make subtle modifications and add parts that either have Executive Order (EO) numbers or components that resemble the factory hardware. If you're affected by the new law, or if your state is considering the same regulations as the Golden State, you'll want to hold onto this article. As you'll soon see, emissions testing doesn't have to spell the end of diesel performance as we know it. In the end, it might even breed a new generation of sleeper performance diesels.

View Photo Gallery | 14 Photos Photo 2/14 | Does this 7.3L Power Stroke engine look stock? Yes. Is it modified? You bet. But how can you tell this engine has bigger injectors, ported cylinder heads, stiffer valvesprings, aftermarket connecting rods, and a modified high-pressure oil pump? The answer is: you can't. The same goes for pre-'07 Duramax and Cummins mills. Things like modified injection pumps will be next to impossible to spot, especially CP3s and even VP44s on '981/2 to '02 Dodges.

Engine

While aftermarket air intakes and intake elbows are pretty obvious to spot, they don't increase the emissions output of an engine and will pass an emissions test. As far as internal modifications go, the truth of the matter is that no one can tell if you're running aftermarket fuel injectors, pistons, rods, heads, or valvesprings. And if you've upgraded any or all of these things in an electronically controlled diesel, aftermarket tuning can dial back the truck's power enough to pass a smoke opacity test.

View Photo Gallery | 14 Photos Photo 3/14 | Cold-air intake systems and air intake elbows will pass a visual inspection, according to the Bureau of Automotive Repair, as they don't alter vehicle emissions.

As mentioned, buy stock-appearing parts, or parts advertised as replacement components when modifying your truck. For example, purchase the turbo that looks similar to the factory unit. One popular turbo upgrade for '991/2 to '03 7.3L Power Strokes is the Garrett GTP38R, which is very similar in appearance to the stock unit. And while some aftermarket turbos are larger externally, they look a lot like the factory turbo (minus the identification tag). The same can be said for many aftermarket turbos for Cummins and Duramax mills. Running virtually any plain-appearing S300, S400, or even a 68mm Cheetah turbo won't look out of the ordinary to the average emissions technician. With these types of upgrades it would be hard for anyone other than a diesel enthusiast to know the difference. Our advice: Don't put that new, polished chrome compressor housing or powdercoated valve cover on. If anything, you want the engine bay to look as inconspicuous (and stock) as possible.

View Photo Gallery | 14 Photos Photo 4/14 | Rest easy if you've replaced your Dodge's factory intake elbow with an aftermarket version. Just make sure your air intake heater is still hooked up and functioning.

Obviously, twin-turbo setups will be hard for the emissions technicians to miss, and twin CP3 injection pumps will be noticeable during a visual inspection. If you're planning on modifying a common-rail Cummins or Duramax we would go with a modified CP3 over a dual CP3 setup. Remember, out of sight, out of mind.

Pull The Programmer

Before you make it to the emissions testing location, remove your performance file from the truck's computer and return it to the stock calibration. If you have a dash-mounted monitor, we'd remove that, too. Even if it only serves as a way to monitor EGT, boost, or coolant temps, you'd be better served to have the least amount of add-ons visible for anyone to see. Be sure to remove any pressure box or underhood performance module before an emissions inspection. Unless you want trouble, avoid vanity plates that say SMOKYA (or anything to that effect). Take your truck down a gravel road to make a nice uniform coating of dust in the engine bay to act as camouflage. Don't bring a vehicle that's just been worked on and washed-it will look suspicious. Have your wife, girlfriend, or sister take the truck to get tested and wait in the background.

View Photo Gallery | 14 Photos Photo 5/14 | Make sure any pressure boxes and underhood modules without an EO number are removed before any emissions test, as they will be a surefire way to fail a visual inspection.

Exhaust

The main cause for concern with exhaust systems is whether or not the truck originally came equipped with a catalytic converter. We've been told that a factory-appearing exhaust will pass, regardless of its diameter, as long as the catalytic converter is in place. For good measure, you could also add a muffler, but to date, we have been told that smog technicians are most concerned with catalytic converters being intact. In addition, you could always reinstall the factory catalytic converter (or even the entire factory exhaust system if you still have it) before your emissions appointment. Larger-diameter downpipes shouldn't be cause for concern because they can't be easily spotted, especially on Power Stroke or Duramax engines. However, it would be safe to say that components like hood stacks and exhaust stacks are out, as are DPF deletes on '08-and-later trucks.

View Photo Gallery | 14 Photos Photo 6/14 | Because exhaust brakes do not alter vehicle emissions, they are considered legal modifications and therefore will pass a visual smog test.

The Good News

Gasoline vehicle smog inspection stations have been around in California since 1966. And, according to the California Air Resources Board, there will be no diesel-specific smog shops, which means truck owners are taking their diesels to smog stations that haven't seen a lot of diesel vehicles before. Since a lot of smog station technicians don't know what to look for-this puts you in the driver seat.

View Photo Gallery | 14 Photos Photo 7/14 | If you've deleted the EGR cooler or want to rid your 6.0L Power Stroke of it, we highly recommend this aftermarket cooler from Neal Technologies. Its EGR cooler is stock in appearance but is much less prone to failing than the factory units.

With dealerships getting in on the emissions game, another loophole will be to take your Ford to a GM shop. Techs there will have little idea where to look for an EGR cooler or EGR valve on a 6.0L Power Stroke. And on the other side of the coin, you could take your Duramax to a Ford dealership, where they might not even discover that the stock turbo has been replaced by say, a Garrett GT4202 turbo.

We know this might sound funny, but have your truck inspected on a windy day. We know that according to CARB, diesels aren't supposed to be checked on windy days, but who can argue with Mother Nature? If you live in an area that typically experiences windy conditions, you'll be in luck during the smoke opacity portion of the test, which is pass or fail (if smoke hovers more than three seconds after a snap test you fail) and is completely at the technician's discretion.

View Photo Gallery | 14 Photos Photo 8/14 | Drop the exterior badges and stickers that suggest anything of a performance nature. Careful inspection of a vehicle wearing badges or decals is warranted, according to the Bureau of Automotive Repair.

Make sure you check out our sidebars, which contain a list of reasons this new law isn't the end of diesel performance, exactly what the law consists of, how you can pass it, and what aftermarket parts you can invest in that won't cause your truck to fail an inspection.

It's really not so bad:

The California Air Resources Board will not be directing diesel vehicles to diesel-specific test stations or Gold Shield stations (testing facilities that follow very strict emissions standards). Furthermore, CARB has no future plans to implement diesel-specific smog stations.

No acceleration simulation mode (ASM) testing will be part of the smoke opacity testing. This means vehicles won't have to run on a loaded dyno (like their gasoline-powered counterparts do) to simulate actual driving conditions.

Trucks with a gross vehicle weight rating (GVWR) of more than 14,000 pounds are exempt, and CARB has no plans to include them in the future. This means '99 to '10 Ford F-450 and F-550s, Dodge Ram 4500 and 5500s, and Kodiak 4500 and 5500s are exempt from being tested.

The law does not apply to the entire state-only areas with dense populations. Inhabitants in 18 of California's 58 counties are exempt from testing. In addition, six counties not exempt from testing do have areas that are considered partially enhanced counties (not everyone has to be smogged).

View Photo Gallery | 14 Photos Photo 10/14 | If your '981/2 to '02 Dodge sports an aftermarket S300 or S400 turbo, we'd recommend dulling up the compressor and exhaust housings to give them an aged appearance. We would also grind off Schwitzer in this case. And due to the lower turbo mounting location on '03 to '10 Dodges, it's even more difficult to take a peak at the turbo to determine whether or not it's stock.

The following gasoline-powered tests are not performed on diesels: EGR functional test, low-pressure fuel evaporative test, fuel cap test, ASM/TSI tailpipe test, and a liquid fuel leak test.

Take a look at the exempt counties (also known as Change of Ownership areas, where owners will only be required to smog their truck before selling it). If you live in one of the following counties you are exempt from testing unless you attempt to sell your diesel: Alpine, Amador, Calaveras, Del Norte, Humboldt, Imperial, Inyo, Lake, Lassen, Mariposa, Mendocino, Modoc, Mono, Plumas, Sierra, Siskiyou, Trinity, Tuolumne. This literature comes from California's Department of Motor Vehicles: "Exemptions applicable to gas-powered vehicles located in non-biennial counties, family transfers, and obtaining a smog for a transfer within the past 12 months will also apply to diesel-powered vehicles."

Aftermarket parts with EO Numbers

Aftermarket parts with Executive Order numbers (EO numbers) have undergone a California Air Resources Board engineering evaluation and have been proven not to increase a vehicle's emissions. Here is a short list of exempt aftermarket parts we found within CARB's database. Many more are likely to have been added by the time you read this, so check with your performance parts supplier before you buy your next upgrade.

View Photo Gallery | 14 Photos Photo 11/14 | As stated, the GTP38R ball bearing turbo (shown here) that's so popular in the7.3L Power Stroke aftermarket looks very similar to stock. The fact that it looks like the factory turbo should keep smog technicians from questioning it.

Dodge performance products with EO numbers:

Year/Engine: '981/2 and '99 24-valve

Company: TST Products

Product: PowerMax module

EO Number: D-503

Year/Engine: '981/2 and '99 24-valve

Company: Edge Products

Product: EZ module

EO Number: D-541

Year/Engine: '981/2 and '99 24-valve

Company: Gale Banks Engineering

Product: Git-Kit, Stinger Kit, Stinger-Plus Kit, and PowerPack Kit

EO Number: D-161-60

Ford performance products with EO numbers:

Year/Engine: '99 to '02 7.3L

Company: Gale Banks Engineering

Product: Git-Kit, Stinger Kit, Stinger-Plus Kit, and PowerPack Kit

EO Number: D-161-61 and D-161-64

Year/Engine: '941/2 to '02 7.3L

Company: Gale Banks Engineering

Product: All OttoMind power modules

EO Number: D-161-63

View Photo Gallery | 14 Photos Photo 12/14 | Don't worry about A-pillar gauges-there are no laws against monitoring how your engine is running. However, if you're relying on a product such as an Edge Juice with Attitude to give you your vital engine information, remove it. This statement comes directly from California's Bureau of Automotive Repair to all smog technicians: "If you observe an exhaust temperature sensor that is installed as part of a non-approved computer system reprogramming device, you must fail the vehicle."

Year/Engine: '941/2 to '03 7.3L

Company: Gale Banks Engineering

Product: All Big Hoss modules

EO Number: D-161-70

Year/Engine: '941/2 to '02 7.3L

Company: Hypermax Engineering

Product: Diesel controller (ECU)

EO Number: D-175-20

Year/Engine: '96 to '02 7.3L

Company: Hypertech

Product: Power Programmer III

EO Number: D-260-10

Year/Engine: '941/2 to '03 7.3L

Company: Superchips

Product: 1705 Max Tuner

EO Number: D-330-7

Year/Engine: '941/2 to '02 7.3L

Company: Bully Dog Technologies

Product: ECU chip

EO Number: D-512-2

Year/Engine: '99 to '02 7.3L

Company: BD Diesel

Product: Performance chip

EO Number: D-553-1

Year/Engine: '941/2 to '02 7.3L

Company: Hypermax Engineering

Product: Intercooler system

EO Number: D-175-21

GM performance products with EO numbers:

Year/Engine: '01 to '03 6.6L

Company: Gale Banks Engineering

Product: Big Hoss programmer

EO Number: D-161-71

Year/Engine: '01 to '03 6.6L

Company: Gale Banks Engineering

Product: Stinger package

EO Number: D-161-72

Year/Engine: '01 to '03 6.6L

Company: Gale Banks Engineering

Product: Six-Gun tuner

EO Number: D-161-74

Year/Engine: '01 to '03 6.6L

Company: Hypertech

Product: Power Programmer III

EO Number: D-260-11

Year/Engine: '01 to '03 6.6L

Company: Edge Products

Product: Edge Juice module

EO Number: D-541-1

What does california's smog test entail?

Smog test every two years (biennial), starting when a vehicle is two years old

View Photo Gallery | 14 Photos Photo 13/14 | If you're using a six-position or other multi-position chip on a 7.3L Power Stroke that piggybacks onto the PCM, simply set the chip to stock, remove the knob or switch from the dash, and zip-tie it up under the dash. An OBD-II test cannot tell if something is attached to the PCM. However, if the adjustable knob is present or visible, a smog technician can investigate its purpose for being there.

No six-year exemption from biennial inspections for new diesel vehicles (like gas-powered vehicles)

No four-year exemption from inspections for change of ownership vehicles (like gas-powered vehicles)

Registering an out-of-state vehicle will require a smog inspection and a certificate of compliance

What the smog test consists of:

Visual inspection for tampering with emissions controls, equipment, and for the presence of non-CARB-exempt emissions-related aftermarket parts (parts without CARB Executive Order numbers)

View Photo Gallery | 14 Photos Photo 14/14 | Even with a set of aftermarket injectors in a 7.3L Power Stroke, the fuel in a performance calibration can be pulled out enough so that no smoke is emitted-maybe even less than stock. Simply talk to your tuner about an emissions tune, which will solve smoke opacity test concerns.

Onboard Diagnostics (OBD-II) interrogation to check for proper malfunction indicator light (MIL) operation, OBD readiness status codes, and any present diagnostic trouble codes (DTCs)

Visible smoke test of the vehicle's crankcase (observed with the engine idling for approximately 10 seconds) and tailpipe at idle. Three snap tests should be performed from engine idle to between 2,000 rpm and 3,000 rpm. The first snap test does not count, the following two do. If smoke lingers for more than three seconds on the second or third test, the vehicle will fail. Nothing should obscure the technician's view of the exhaust plume (and a white backdrop is suggested). Again, this is completely at the technician's discretion.