6.7 Cummins Emissions Systems
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6.7 Cummins Emissions Systems

Jake Mayock

Meet Jake

Jake is a founder of 8020 Media and one of the lead writers at DieselIQ. He has over 10 years of experience in the automotive industry and is the proud owner of a 2002 F-350 7.3 PowerStroke. When Jake isn’t working, he’s usually wrenching on his PowerStroke, single turbo BMW, or Miata track build. Jake delivers tons of knowledge and hands-on experience and is a valuable asset for those looking to take their diesel to the next level. He is highly knowledgeable on Powerstroke and Duramax diesels.

Diesel fuel is a lot less refined than traditional gasoline which means it burns dirtier and releases more harmful exhaust gases. Starting around 2007, diesel emissions standards started to become a huge focus point. Today, all diesel engines have a number of emissions systems, including exhaust gas recirculation (EGR), diesel particulate filters (DPF), selective catalytic reduction (SCR), and various specialized catalytic converters.

This guide will discuss the different harmful gases that diesel engines produce along with every emissions system used by the 6.7 Cummins and its purpose for reducing emissions. Since deleting emissions systems is common on diesel engines we’ll include some brief commentary at the bottom about the benefits and downsides of 6.7 Cummins emissions deletes.

6.7 Cummins Emissions Systems

6.7 Cummins Exhaust Byproducts

Before we dig into the various components of the 6.7 Cummins emissions equipment, we need to cover the primary byproducts of diesel engine combustion. These are the harmful exhaust gases that are produced as a result of burning diesel fuel.

Carbon Dioxide CO2

Carbon dioxide is a greenhouse gas. As humans, we release carbon dioxide when we exhale. So is it really that bad? Carbon dioxide traps heat within the atmosphere and is believe to be one of the leading causes of global warming. Because humans only exhale the carbon dioxide that we inhale, we don’t actually increase the amount of carbon dioxide in the atmosphere.

However, when we burn fossil fuels, such as diesel fuel, it creates carbon dioxide that otherwise wasn’t present in the atmosphere. Therefore, reducing the amount of it that is released to the atmosphere via diesel exhaust gases is important.

Nitrous Oxides – NO, NO2, NOx

NOx is nitrous oxides which includes nitric oxide (NO) and nitrogen dioxide (N02). NOx gases are produced as a chemical reaction between nitrogen and oxygen during diesel engine combustion. Nitrous oxides create smog, which is air pollution that reduces air visibility. It is also dangerous to people who have preexisting breathing conditions.

Diesel Particulates

Diesels release particles or particulate matter through their exhaust gases. These are very small particles that are considered carcinogens. When breathed in by a human they can get stuck to the lining of the lungs and have various health effects. Don’t worry, this doesn’t mean owning a diesel will be harmful to your health.

Components of the 6.7 Cummins Emissions System

To reduce the amount of harmful byproducts that are released into the atmosphere, the 6.7 Cummins is packed with a number of advanced emissions systems. These systems have gotten a bad rap over time and are frequently deleted or removed from the vehicle. First of all, they are extremely expensive. Since the majority of this equipment is some form of catalytic converter, it is packed with expensive rare earth metals making the products expensive to replace.

Additionally, they create a lot of backpressure within the exhaust system which is bad for the turbocharger and increases exhaust gas temps. Furthermore, they are all prone to clogging which further exacerbates the backpressure and heat issues. And lastly, they are detrimental to engine performance and gas mileage.

However, they are all required and are crucial components for reducing harmful emissions produced by the 6.7 Cummins.

Exhaust Gas Recirculation (EGR): 2007.5-Present

EGR isn’t a diesel-only concept, virtually all engines use some form of exhaust gas recirculation. Beginning in 2007.5 model years, the 6.7 Cummins added an EGR system which includes an EGR valve and an EGR cooler.

The system works by taking exhaust gases and recirculating them through the intake manifold back into the combustion chamber. This allows the exhaust gas to be re-burned in the combustion chamber which reduces the amount of harmful byproducts.

Once the exhaust air leaves the combustion chamber it passes through the diesel particulate filter (DPF). Then, a portion of gases flow to the rest of the exhaust system and a portion flow into the EGR cooler. The EGR cooler cools down the air that is going to be passed back into the intake system. After the cooler is an EGR valve that is connected to the intake throttle body. This valve opens and closes, controlling the amount of exhaust gas that is sent back to the intake system.

Diesel Oxidation Catalyst (DOC): 2007.5-Present

A diesel oxidation catalyst, or DOC, is simply a catalytic converter designed specifically for diesels. For 2007.5-2012 model years the DOC is integrated into the 6.7 Cummins downpipe, which bolts directly to the turbocharger. 2013+ models years simply used a flex pipe as a downpipe.

The DOC in later model years is integrated into the DPF system and does not sit within the downpipe which is a common misconception.

NOx Absorption Catalyst (NAC): 2007.5-2012

The 6.7 Cummins SCR system wasn’t integrated until 2013. Prior to the SCR system, a NOx absorption catalyst was used. The exhaust system for 2012 and prior goes like this: DOC to NAC to DPF and then out the tailpipe. In 2013, with the addition of SCR, NAC was removed, and therefore the exhaust systems flows: DOC/DPF to SCR and then out the tailpipe.

The NAC catalyst captures nitrogen oxide and converts it into pure nitrogen and oxygen gases. Again, it is similar to a traditional catalytic converter but specific to diesel NOx emissions. This system does require undergoing a regeneration process to remove sulfur deposits that buildup in the catalyst.

Diesel Particulate Filter (DPF): 2007.5-Present

As we discussed above, diesel engines release particulates which is also commonly called diesel soot. The DPF system is a honeycomb filter, similar to a traditional catalytic converter, that captures and collects particulate soot.

The 6.7 Cummins has had a DPF system since halfway through the 2007 model year. 2007.5-2012 models had a completely separate DPF system that sat behind the DOC system. In 2013+ models the DOC and DPF were integrated together.

DPF systems require “regeneration cycles”. As the DPF system collects soot it eventually fills up and needs to burn the soot or clear it out to be able to capture more particulates. Once the DPF has built up too much particulates, the backpressure experience in the exhaust system increases. This triggers a regeneration cycle.

There are two regeneration cycles: passive and active. Regeneration is the process of burning the particulate matter. Doing so requires high temperatures and essentially incinerates the built up soot into harmless ashes which need to be cleaned out from time to time.

Passive Regeneration

Passive regeneration occurs naturally as you drive. Once exhaust gas temperatures reach 950 degrees Fahrenheit or higher, the soot naturally burns into ash. However, reaching these EGTs doesn’t happen from just driving your 6.7 Cummins to the store and back and therefore active regeneration is also required.

6.7 Cummins Active Regeneration

Since high enough EGTs aren’t always achieved, active regeneration needs to take place. During active regeneration, diesel fuel is injected into the exhaust stream. The fuel flows over the oxidation catalyst (DOC) which oxidizes the fuel and creates heat. This heat then burns the soot into carbon dioxide.

Selective Catalytic Reduction (SCR) & DEF Fluid: 2013-Present

The SCR system sits after the DPF system. Since the DPF system burns diesel particulates into carbon dioxide, the SCR system is in place to reduce the produced carbon dioxide.

The selective catalytic reduction system required diesel exhaust fluid, or DEF fluid. DEF is a fluid made of urea and water. This fluid gets injected into the SCR catalyst where a chemical reduction reaction takes place. The reduction reaction converts the carbon dioxide into water and nitrogen gas.

Deleting 6.7 Cummins Emissions Systems

As discussed above, these emissions components are not only expensive but are also prone to failure. If you checkout our 5 most common 6.7 Cummins engine problems, the DPF and EGR cooler are two of the most common issues. DPF clogging and backpressure created by these emissions system can also cause turbo failure.

Outside of the costly repairs they can cause, they also limit performance by creating a lot of backpressure. In order to bring more air into the engine and create more power through higher turbo boost levels, backpressure needs to be minimized. Backpressure inhibits a turbos ability to spool quickly and creates resistance against the turbine wheel.

All that said, deleting the DPF and EGR systems is very common. However, it is also very illegal.

Benefits of 6.7 Cummins Emissions Delete

  • Improved reliability
  • Removes components that are costly to replace
  • Decreases turbo backpressure / more free flowing exhaust
  • Increases performance potential
  • Improves mpg slightly

Why You Shouldn’t Delete Your 6.7 Cummins Emissions

  • It is illegal
  • It voids warranty
  • Dealers won’t touch your car, a lot of independent shops won’t anymore either
  • Hurts resale value
  • Creates problems with vehicle registration and renewal

There are really two reasons people delete these systems: they don’t want to pay $5k for a new SCR, or they don’t want to restrict performance. I get it, the cost of these parts are expensive which makes breaking them concerning. However, from a performance perspective. Unless you are chasing crazy performance numbers, the 6.7 Cummins is completely capable of punching out some extra power with some simple legal mods like an intake and a tune.

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  1. when will the authorities stop foot dragging and support laser drilled inj nozzles that make for superior combustion

  2. Your argument to not do a delete takes me back to the days 1n the 60’s when we were advised not to smoke marijuana. Not everyone is looking for more power. My stock 2017 Ram 3500 drw has all the power I want. What it doesn’t have is Economy. Driving without a load is not much different than traveling with my 35ft. fifth wheel. 24 to 29 litres per 100 kilometres.

    1. David – if you want fuel economy benefits I’d start with an intake and a tuner. You can run a tuner both without load and while towing for better gas mileage. Sure, deleting the DPF goes a bit further and helps even more, but there are other options to start with. Also, I’m not sure what the arguments were back in the 60’s but there is absolutely more focus on environmentalism and pollution nowadays.

      My whole point was that if you don’t need more power, then you don’t need to delete the DPF. Leave it on, toss on a tune, and get an intake and you’ll see enough mpg benefits. Or, if you can’t afford the poor fuel economy, get a smaller camper and go pick up an EcoDiesel.

  3. If “DEF’ fluid is older than 2 years can it cause a warning light to come on? If so, will the vehicle eventually go into “limp” mode?

    1. Yes. DEF goes bad over time, especially in hot weather. Shelf life at 104 degrees is 4 months and about a year at room temp. Good idea to drain DEF tank and replace with new fluid in warm climates every 6 to 10 months.

  4. Hmm, dealer has had my truck for four months trying to fix this government mandated piece of sh** system. Problem first appeared at <13,000 miles in November 2020. Been in and out of dealer service over a dozen times since then for the same problem. Been there since May this time and now it's worse. Can't even get down the road without the CEL coming on. I used to be able to at least get 1,000 miles or so out of it. I don't really care how they're supposed to work or what they allegedly do for "mah environment", I want them off of all vehicles. The first step in dismantling the gigantic bureaucracy and huge special interest groups that just love these systems is for an empowered collective to remove them wholesale and make it distasteful and highly prohibitive to enforce these bullshit mandates. For myself, I know what's happening when(if) I get my truck back.

    1. Well said! These systems increase overall fuel consumption, increase maintenance and costs for the consumer, and the rare earth minerals have a huge carbon footprint due to the extraction-transport and processing.

      All of this is extremely bad 4 environment, so I’m not sure how a truck getting 16mpg with all the “embodied energy” of this emissions crap is any better for the environment than the same truck w/out the emissions junk @ 19mpg?

      The politicians are using fuzzy logic and special interest oil $ to justify these mandates….

  5. If the real goals were environmental, we’d all have access to cheap B-100! Biodiesel grown in the USA creating sustainable and independent fuel for the American economy, and it’s better for the engine with a higher lubricity & neutral CO2 quotient.

    Rudolf Diesel never wanted his engine run on petroleum based fuel. When he introduced it to the world at the 1912 World Fair it was run on linseed oil.

    These emissions systems increase overall fuel consumption, increase maintenance and costs for the consumer. The rare earth minerals used in the catalysts have a huge carbon footprint due to the extraction-transport and processing (not to mention the geo-political impacts)!

    All of this is extremely bad 4 environment, so I’m not sure how a truck getting 16mpg with all the “embodied energy” of this emissions crap is any better for the environment than the same truck w/out the emissions junk @ 19mpg?

    The politicians are using fuzzy logic and special interest oil $ to justify these mandates under the guise of “environmental protection”

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